I use these notes to remember various Linux commands and procedures. When I learn something new, a section gets appended to the document. I appreciate hearing about errors.
Making a Linux cheat sheet is a popular activity. The following link will give you an up-to-date list:
If you know where you want to go, you can enter the section name as part of the browser URL. The browser will adjust the view to show the proper part of the document. Example:
http://www.csparks.com/LinuxCommands.xhtml#toc_audio
The anchor name, in this case "toc_audio" is created by prepending "toc_" onto the section name in lower case. Use hyphens where spaces appear in the name. Only top level sections have anchors.
ServerName www.yourdomain.com
ServerAdmin you@yourdomain.com
apachectl configtest
telnet some.server.com 80
GET /whatever.html HTTP/1.1
host: your.host.com
<enter another LF>
A container is a group of directives that apply to requests that have a common path. The container is said to match the path. The path may be an actual file system path on the server or an abstrct path that appears in a URL after the server name.
The directives in a container commonly apply access and authentication rules or invoke other programs to process the request.
The following sections describe three basic containers: VirtualHost, Directory, and Location.
Virtual hosts allow one physical server to appear as many others, each with its own IP name.
Add this global directive:
NameVirtualHost *
Each virtual host has a container for additional directives:
<VirtualHost *>
ServerName myHost.myDomain.com
DocumentRoot /var/www/html/myDirectory
...
</VirtualHost>
You must have a CNAME entry for myHost in your zone file or a definition for myHost.myDomain.com in your /etc/hosts file.
A directory container should be always be used when dealing with documents in the file system:
<Directory /home/user/www>
Order deny,allow
Deny from 192.168.2.23
...
</Directory>
Location sections match paths in URL space. They may trigger webapps or refer to other resources that have nothing to do with the file system. Location directives are applied last and override the effect of overlapping Directory containers. It is unwise to use Location containers to match file system paths.
<Location /jeuler>
ProxyPass ajp://localhost:8009/jeuler/
ProxyPassReverse ajp://localhost:8009/jeuler/
</Location>
Some browsers won't display xsl formatted xml documents unless the associated xsl file is served with the appropriate mime type (text/xml or application/xml) This can be configured by adding these directives:
AddType application/xml .xml
AddType application/xml .xsl
The server will accept or reject requests based on rules. The rules can be categorized by what part of the request they examine:
Access:
Access rules discriminate based on the IP number of the client.
Authentication:
Authentication rules discriminate based on a username and
password supplied by the client.
Authorization:
One a client has passed the access and authentication
barriers, authorization rules determine what the client
is allowed to do.
Limits:
Limit rules apply different authorization rules depending
on the request type.
A common cause of confusion is that Apache sets up defaults for access and authentication as well as rules that control arbitration between them. If these rules are not explicitly stated in your sections, it's impossible to understand how the directives work or why things don't work the way you expect.
To diagnose access problems:
tail -f /var/log/httpd/error_log
Basic authentication sends clear text passwords over the web, so it's not safe to use by itself. It can be used securely over SSL (https://) connections. There is a trend among "user friendly" operating systems to bully users into avoiding basic authentication over unsecure channels.
Authentication directives are used inside Directory or Location sections:
Example:
<Directory /var/www/html/privateStuff>
AuthType Basic
AuthUserFile /etc/httpd/users.htpasswd
AuthName "Access to private stuff is restricted"
require valid-user
</Directory>
The AuthName message gets displayed by the client's browser when it pops up a dialog window requesting the username and password.
The directive "Require valid-user" allows access to anyone who appears in the htpasswd file. Alternatively, you can allow access for selected users:
require user bevis mary
Creating a password file:
htpasswd -c /etc/httpd/users.htpasswd aUserName
The program will prompt for the password. The password file SHOULD NOT be located under any Directory section controlled by the server.
Adding a user to the password file:
htpasswd /etc/httpd/users.htpasswd aUserName
The program will prompt for the password.
Deleting a user from the password file:
htpasswd -D /etc/httpd/users.htpasswd aUserName
Digest authentication uses encryption, so it's a better choice for regular http:// access.
Digest directives can be added to Location or Directory sections. For a Location:
<Location /thisLocation>
AuthType Digest
AuthName Administrators
AuthUserFile /etc/httpd/users.htdigest
AuthDigestDomain /thisLocation /someOtherLocation ...
require valid-user
</Location>
The AuthName has a specialized meaning here: it names a "realm". Realms are an abstraction used to group one or more locations on the server you want to protect as a unit.
Each line in the AuthUserFile contains a username, password, and realm name. This allows the administrator to have one AuthUserFile for all the authentication rules.
Realms control access to the path named in the Location directive and all "sub paths" relative to that location: In the example above, a path such as "/thisLocation/here" is also part of the realm.
Most browsers allow users to "Remember my password" when they are prompted to enter credentials. The AuthDigestDomain directive lists other paths protected by the same credientials so the user won't have to enter them again. The browser quietly submits the previously used credentials when any of the other paths are used.
To construct the parameter list for AuthDigestDomain, simply list all the path expressions used in Location and Directory sections names that have the same realm.
Creating a digest password file and adding the first user:
htdigest -c /etc/httpd/users.htdigest aRealm aUserName
The program will prompt for the password.
Adding a user to the digest file (or changing an existing user's password):
htdigest /etc/httpd/users.htdigest aRealm aUserName
The program will prompt for the password.
Deleting a user:
The htdigest command doesn't have a delete option. Just edit the .digest and delete the line with the username you want to remove.
Groups allow you to define sets of users. They can be used with any authentication type.
To use a group called "slackers", add these directives:
Require group slackers
AuthGroupFile /etc/httpd/users.htgroups
In this example, a user must authenticate as usual and in addition belong to the group "slackers"
The file users.htgroups may define any number of groups and the users who belong to them. Each line in the file begins with a group name followed by the user names that belong:
administrators: fred kevin jane
slackers: judy steve
As with other authentication data files, it's best to keep the groups file out of the server's Directory scope.
Individual ip addresses:
Allow from 192.168.2.3
Deny from 192.168.2.4
Subnet expressions - These two directives are equivalent:
Allow from 192.168.1.0/255.255.255.0
Allow from 192.168.1.0/24
The order in which allow and deny tests are applied is important. There are three choices:
Order allow,deny
Everyone starts out denied. Allow rules are processed first, then deny rules. If an allow rule lets them in, a deny rule will throw them out.
Order deny,allow
Everyone starts out allowed. Deny rules are processed first, then allow rules. If a deny rule throws them out, an allow rule will let them in.
Order mutual-failure
Everyone starts out denied. Client must match an allow rule and NOT match a deny rule.
Example - Allow everyone:
Order allow,deny
Allow from all
Example - Exclude everyone:
Order deny,allow
Deny from all
Example - Allow only one subnet:
Order deny,allow
Deny from all
Allow from 192.168.1.0/24
Example - Allow only specified clients:
Order allow,deny
Allow from 192.168.1.2 192.168.1.3
Example - Allow only one subnet and exclude one of those clients:
Order allow,deny
Allow from 192.168.1.0/24
Deny from 192.168.1.7
Access and authorization directives are always in effect. They may be specified explicity in sections or inherited from the top level server configuration.
The "Satisfy" directive determines how they are combined. Clients must pass access AND authentication control:
Satisfy all
Clients must pass access OR authentication control:
Satisfy any
Allow local LAN users without authentication but require authentication from all others:
Satisfy any
Order deny,allow
Deny from all
Allow from 192.168.1.0/24
AuthType Basic
AuthName "Special area"
AuthUserFile /etc/httpd/users.htpasswd
Require valid-user
Require everyone to authenticate:
Satisfy all
Order allow,deny
Allow from all
AuthType Basic
AuthName "Special area"
AuthUserFile /etc/httpd/users.htpasswd
Require valid-user
Allow users from only one subnet and they must authenticate:
Satisfy All
Order deny,allow
Deny from all
Allow from 192.168.1.0/24
AuthType Basic
AuthName "Special area"
AuthUserFile /etc/httpd/useres.htpasswd
Require valid-user
The Limit directives allow the server to apply different rules depending on the type of request. (Sometimes called the "request method")
The top level server configuration file normally has hese default rules that allow everyone to see content on the site but not modify the site:
<Limit GET POST OPTIONS PROPFIND>
Order allow,deny
Allow from all
</Limit>
<LimitExcept GET POST OPTIONS PROPFIND>
Order deny,allow
Deny from all
</LimitExcept>
Everything inside the
The following example lets everyone read the site, but restricts writing to authorized users:
! Allow access from any ip address:
Order allow,deny
Allow from all
! Setup authentication by password
AuthType Basic
AuthName "Special area"
AuthUserFile /etc/httpd/users.htpasswd
Require valid-user
! Decide how to combine authentication and access rules
! based on the request type:
<Limit GET PROPFIND OPTIONS REPORT>
! Let anyone read
Satisfy Any
</Limit>
<LimitExcept GET PROPFIND OPTIONS REPORT>
! All other requests need authentication
Satisfy All
</LimitExcept>
In this example, files that end with ".xml" or ".mml" are rewritten to find them in the "mxyzptlk" directory:
RewriteEngine on
RewriteCond %{REQUEST_URI} !(^/mxyzptlk/.*)
RewriteRule (.*)\.(xml|mml)$ mxyzptlk$1.$2 [P]
Using these rules, the client browser will show the orignal URL in the address display, not the rewritten version.
To fix this error:
"...No space left on device: mod_python: Failed to create global mutex..."
Execute this command:
ipcrm sem `ipcs -s | grep apache | cut -d' ' -f2`
Getting apache to serve WebDAV content to Windows clients is notoriously difficult. See if you like this method:
First, you need a lock file directive in the Apache configuration file.
On linux this could be:
DAVLockDB /var/lib/dav/DavLock
If you're running apache on Windows, use the expression:
DAVLockDB var/DavLock
The "var" directory in the Windows case is a directory you create in the Apache installation root directory.
The following examples use an Apache Directory section, but the same configuration can be used inside Location or VirtualHost sections.
Alias /webdav /var/www/webdav
<Directory /var/www/webdav>
DAV on
Satisfy all
Order allow,deny
Allow from all
ForceType application/octet-stream
AuthType Digest
AuthName "davusers"
AuthDigestDomain /webdav /fleep /goop /dreep
AuthUserFile davusers.digest
Require valid-user
Options Indexes
</Directory>
Create the digest authentication file:
htdigest -c /etc/httpd/davusers.digest "davusers" yourUserName
The parameter "davusers" is the name of a realm - The realm concept allows one file to contain credentials for multiple services and/or locations. In this case, we are using the realm "davusers."
You will get a prompt for a password and the file will be created. Adding more users to the realm is similar, but leave out the -c switch, which creates a new file erasing the old one. As the syntax suggests, htdigest can store many users with multiple realms all in the same file.
This is a better method but it depends on having SSL configured on your server. Other than the aggravation of buying and configuring a certificate, this method seems to make Windows behave better - There are no more mysterious recursive directories and the protocol is easier to specify:
Alias /webdav /var/www/webdav
<Directory /var/www/webdav>
DAV on
Satisfy all
Order allow,deny
Allow from all
ForceType application/octet-stream
AuthType Digest
AuthName "davusers"
AuthDigestDomain /webdav /fleep /goop /dreep
AuthUserFile davusers.digest
Require valid-user
SSLRequireSSL
Options Indexes
</Directory>
Configure the digest file as described in the previous section. When you specify the url on the Windows side, you don't need the port number mumbo-jumbo:
https://www.yourPlace.com/webdav
Clearly, the SSL certificate must be created to exactly match the server name. You can also use this method inside a virtual host if the name matches the certificate.
The parameters to AuthDigestDomain consist of path expressions used to access all locations associated with the same digest realm. This information is sent to the client browser so the user won't have to re-enter the same credentials for locations specified in the directive after they have been prompted for one of them.
In the examples above, the "davusers" realm is being used to protect our /webdav location. It also protects locations /fleep /goop /dreep. These locations would be described by other Apache sections. Each of the other sections should contain the same expressions:
AuthName "davusers"
AuthDigestDomain /webdav /fleep /goop /dreep
You might think that Apache would be smart enough to figure this out since the two sections each have the same realm. But for some reason, it must be specified.
In the previous examples, replace the directive "Require value-user" with this section:
<LimitExcept GET HEAD OPTIONS>
Require valid-user
</LimitExcept>
On the Windows XP side, open "My Network Places" and double-click "Add Network Place". Hit "Next", then select "Choose another network location" and hit "Next" again. Enter a url for the virtual host in this form:
http://www.yourPlace.com:80
The wizard will grind away and then prompt for the username, password, and a name for the shortcut. The new shortcut will be added to the "My Network Places" folder. Note the appended port number: It is important. It somehow short-circuits Microsoft's attempt to discourage the use of the WebDAV protocol.
On the Windows 7, right-click on "My Computer" and select "Map Network Drive..." Enter a folder path in this form:
https://www.yourPlace.com/webdav
If you don't have "My Computer" on your desktop, you can do the deed from any Explorer (not Internet Explorer) window:
File menu->Add a network location
Select "Choose a custom network location..."
Press "Next"
In the "Internet or network address:" box, use a URL of the form:
https://www.yourPlace.com/webdav
Note that your really must have SSL setup to make webdav work smoothly with Windows 7 and beyond. There are work-arounds that involve modifying the registry...
Internet Explorer->Tools->Internet Options
Select the Connections tab.
Press the "LAN Settings" button.
UNCHECK: "automatically detect settings"
You can't really imagine how slow webdav will be unless you do this.
Windows XP and Vista clients need a patch to fix multiple webdav bugs. I used to maintain a link here, but Microsoft keeps shifting things around. Just do a search for "KB907306" and you'll find it without difficulty. Note: Windows 7 and later versions don't need this patch.
UPDATE: As of Windows 10, webdav works without fuss. Microsoft relented.
This is a marvelously obsure bug. I suspect it has happened to others. The symptom on the Windows side: Users can map the webdav directory and copy files from the server. But when they try to copy a file to the server, an error pops up:
Can't read from source file or disk
Watching the logs on the apache server, we see these lines:
Could not open the lock database
...
Permission denied: Could not open property database
It turns out to be caused by corruption of the lock database. I have no idea how this happens, but the fix is simple: stop the server, delete the lock files and restart:
service httpd stop
rm -f /var/lib/dav/lockdb.dir
rm -f /var/lib/dav/lockdb.pag
service httpd start
The lock files will be recreated and windows clients will have read/write access to the webdav directory.
Normal unix-to-unix with locally mounted paths:
rsync -ax --numeric-ids --delete sourceDir/ destDir
The trailing / on the sourceDir is very important: It means copy the contents of sourceDir into destDir, rather than copying the sourceDir itself.
If you have ssh setup from the source to the destination machine, backups are fast and easy to do over the network.
If you can do this successfully: (See the SSH section in this document.)
ssh user@remote.com
Then you can do this:
rsync -ax -e ssh --delete sourceDir/ user@remote.com:/path/to/sourceDir
Note that the /path/to/sourceDir is the path as seen on the remote machine. You can also pull data from a remote machine by reversing the source and destination parameters.
You can also rsync to or from network mounts via nfs or samba. If you rsync between linux and windows machines using samba, all sorts of permission and symbolic link problems are likely.
The rsync command is great for copying large things because you can see progress:
rsync -ah --progress sourceFiles destDir/
Backup to a vfat or smb filesystem using only time attribute: (Pulling from the linux side.)
rsync -a --delete --exclude-from="excludeNT.txt" sourceDir/ destDir
The excludeNT.txt file contains the names of files that should not be copied. They are locked system files that will cause error messages if not excluded during the backup. You can include a path prefix when necessary, but the name of the file alone is sufficient if it's not likely to appear anywhere in your personal files.
ntuser.dat
NTUSER.dat
ntuser.dat.LOG
NTUSER.DAT.LOG
UsrClass.dat
UsrClass.dat.LOG
hiberfil.sys
pagefile.sys
Other applications running on Windows may lock files. By observing the messages from rsync you can add to the list and achieve a quiet backup.
tar czf arch.tgz path # Make an archive (Add v for verbose)
tar xzf arch.tgz # Restore an archive (Add v for verbose)
tar tf arch.tar # List an archive
Other tar options
-C directory # Change to this directory first
-T fileList # Use this list of file names
--same-owner # Keep original owner when extracting
--same-permissions # Keep original permissions when extracting
--absolute-paths # Don't strip leading /
--directory dirPath # Change to this directory first
--files-from=fileList # Get file names from another file
gzip file
gunzip file.gz
zip -r archive.zip files...
unzip archive.zip
tar cf - $thing -P | pv -s $(du -sb $thing | awk '{print $1}') | gzip > $thing.tgz
Mode of operation is one of "pio":
p Pass files through without using an archive file
i Extract from an archive
o Create an archive
Other common options:
t List the contents of the archive
m Preserve modification times
d Create directories as needed
u Overwrite files without warnings
cpio -mid < archive.cpio
List the archive to see if it has absolute names. Use --no-absolute-filenames if necessary. This doesn't happen very often, but if it does and you are root a Bad Thing (tm) can happen.
cpio -t < archive.cpio
Includes invisible dot files. Preserves all dates.
find . | cpio -pudm targetDir
On modern Linux systems "cp -a" will do the same thing.
find . | cpio -o > archive.cpio
play test.wav
On these systems, /dev/dsp is always tied up by artsd. Use the artsdsp command to run any program that would normally access /dev/dsp directly:
artsdsp play test.wav
Record a "normal" stereo wav file:
rec -c 2 -f U -r 44100 -s w -v 8.0 test.wav
Record options:
-c 2 Two channels (stereo)
-r 44100 Sample rate
-f Sample encoding:
s Signed linear (2's compliment)
u Unsigned linear
U U-law (logarithmic) U.S. standard
A A-law (logarithmic) EU. standard
a ADPCM (Adaptive Differential Pulse-Code Modulation)
i IMA_ADPCM
g GSM
-s Sample size:
b 8 bit bytes
w 16 bit words
l 32 bit long words
f 32 bit floats
d 64 bit floats
D 80 bit IEEE floats
-t File format:
au Sun
cdr CD track
gsm GSM 06.10 Lossy Speech Compression
wav Windows RIFF (Header contains all params)
-v Set the volume
1.0 No change
2.0 Linear increase by 2.0
0.5 Linear decrease by 2.0
8.0 About right to balance with other .wavs
The file format can be specified by giving the file a matching extension.
ADPCM, IMA_ADPCM & GSM are intended for speech compression. U-law would be appropriate for music.
esdplay
Some people make this an alias for 'play'
esdrec | esdcat
mpg123 yourfile.mp3
First run:
mpg123 -s yourfile.mpg > yourfile.raw
The above command will display the sample rate and the number of channels. (Mono or Stereo)
The output is 16 bit, signed pcm, little endian. No header.
sox -c 2 -w -s -r xxx yourfile.raw yourfile.wav
The xxx value must be the sample rate displayed by mpg123. You can pipeline mpg123 into sox. Use a - for the sox input.
An easier way to do both steps:
lame --decode yourfile.mp3 yourfile.wav
sox inputOptions inputFile outputOptions outputFile
Do a "man soxexam" to see many examples.
Format options:
Channels
-c n Where n = 1,2 or 4
Sample rate
-r rate Where rate is in Hertz
Sample size
-b 8 bits
-w 16 bits
-l 32 bits
Encoding
-s Signed linear
-u Unsigned linear
-U U-law (U.S. logarithmic)
-A A-law (Euro logarithmic)
-a ADPCM (Adaptive pulse-code modulation)
-i IMA_ADPCM
-g GSM
-f Floating point
Input file format is controled by the file extension:
.wav (You don't need to specify other options)
.au (Options may or may not be needed)
lame [-b bitrate] infile.wav outfile.mp3
lame [-b newbitrate] --mp3input oldfile.mp3 newfile.mp3
ffmpeg -i myVideo.flv -ab 128k myAudio.mp3
mplayer -novideo -ao pcm:file=result.wav source.avi
for f in *.flac; do ffmpeg -i "$f" -ab 196k -map_metadata 0 "${f%.flac}.mp3"; done
Variables are created by assignement:
strVar='This is a string'
numVar=123
They are referenced using the dollar prefix:
newVar=$oldVar
Concatenation of strings is implied:
newVar='This is ' $oldVar
Note: Spaces are not allowed around the = symbol.
Undefining variables:
unset myVar
Enclose the command in back-quotes: Example: getting the size of a directory
dirSize=`du -s myDirectory | awk '{print $1}'`
The string should be pipelined to this command:
awk '{print $n}'
Example:
SIZE=`du -s -k myPath/myDir | awk '{print $1}'`
if [$SIZE -gt 4096]; then
echo "The directory myDir contains more than 4096kb"
fi
This example returns the free memory of the machine, which appears in the middle of the second line of /proc/meminfo. Note the escapes required on nested quotes:
sh -c 'echo $4' `cat /proc/meminfo`
awk "NR=123 {print;exit}" myfile.txt
cat > myPath/myFile <<- 'EOF'
line1
line2
...
lineN
EOF
-d Is a directory
-e Exists
-f Is a regular file
-h Is a symbolic link
-r Is readable
-s Size is > 0
-w Is writable
-x Is executable
Example:
if [ -e <path> ] ; then
# Do this if file exists
fi
if [ ! -d <path> ] ; then
# Do this if it's not a directory
fi
-z <astring> # Length of string is zero
-n <astring> # Length of string is non-zero
-nt Newer than. Or file1 exists and file2 does not.
-ot Older than. Or file2 exists and file1 does not.
if [ <file1> -nt <file2> ] ; then
Do this if file1 is newer than file2 (or file2 does not exist)
fi
=, !=, <, >
-eq, -ne, -lt, -le, -gt, -ge
NOT prefix operator: !
AND operator: &&
OR operator: ||
If-then-else:
if [ -e $pathname ] ; then
# It exists
elif [ -e $thatname ] ; then
# That exists
elif [ -e $theOther ] ; then
# The other exits
else
# They don't
fi
Case statement:
In this example, prepending "x" makes the construct work even if GOOB is undefined. Quoting variable expansion is always a good idea when whitespace may be present in the value.
GOOB=def
case x"$GOOB" in
xabc)
echo abc
;;
xdef)
echo def
;;
*)
echo unknown
;;
esac
Iteration:
myDirs="dev etc bin proc mnt tmp var lib"
for dir in $myDirs ; do
mkdir $targetRoot/$dir
chmod u=rwx,og=rx $targetRoot/$dir
done
for i in 121 19 34 56 78; do
echo $i
done
for i in `seq 1 10`; do
echo $i
done
for ((i=1; i<=10; i+=1)) ; do
echo $i
done
line="&test1=a1&test2=a2"
while [ $line != "" ]; do
a1=`echo $line | sed -e 's/.*&//'`
line=`echo $line | sed -e "s/&"$a1"//"`
echo $a1
done
count=10
until [ $count -lt 1 ]; do
echo $count
let count=count-1
done
$0 Name of the script or function
$1 ... $n Each parameter
$@ All parameters starting with $1
$# Number of parameters
$? Exit status of last bash command
To shift all parameters left by 1: $1=$2, $2=$3 etc:
shift 1
You can shift by any positive n.
Local functions work like shell scripts. They have their own $0..$n parameters:
function demo
{ echo Function: $0
echo Param 1: $1
shift 1
for i in $@ ; do
echo Arg: $i
done
}
demo special 123 456 789
Historical note: Instead of "function demo" to start a function definition, the form "demo()" is allowed. This notation confounds the unwashed because they wish they could put a formal parameter list inside the ()s.
Every bash script or function returns a numerical status. A non-zero status denotes failure.
To exit a script immediately and return failure:
exit 1
To exit with success:
exit 0
If the script runs off the end, "exit 0" is implied.
if [ $# -eq 3 ] ; then
echo Usage: $0 arg1 arg2 arg3
exit 1
fi
while [ $# -gt 0 ] ; do
echo $1
shift
done
for line in `cat myfile.txt`; do
echo $line
done
select opt in "Hello Goodby"; do
if [ $opt = "Hello" ]; then
echo Hello there!
elif [ $opt = "Goodby" ]; then
echo done
exit
else
clear
echo Try again...
fi
done
exec 3< MyFile.txt
while [ ! $done ] ; do
read <&3 myline
if [ $? != 0 ]; then
done=1
continue
fi
echo $myline
done
Redirecting selected streams to a file:
1> Only stdout
2> Only stderr
&> Combine stdout and stderr
The &> is often, but not aways, the default behavior of a command. It is a Bash-only construct. A more portable way to do the same thing is:
2>&1 Combine stdout and stderr
Suppress error messages when running a command:
myCommand 2>/dev/null
Assume the current directory contains a file:
exists
And assume that this file does not exist:
nosuch
A command that partly succeeds:
ls -l exists nosuch
Console will show the exists listing and an error about nosuch.
Send stdout to a file:
ls -l exists nosuch > Demo
Console shows "exists" listing and error about nosuch. Demo contains only the "exists" listing.
Send stderr to a file:
ls -l exists nosuch 2> Demo
Console shows only the "exists" listing. Demo contains only the error message about nosuch.
Add stderr to stdout and redirect to a file:
ls -l exists nosuch 2>&1 1> Demo
Console shows the error about "nosuch." Demo contains only the "exists" listing.
Note the precidence:
First stdout goes to Demo. Then stderr replaces stdout and goes to the console.
Add stderr to stdout and pipeline result to another program:
ls exists nosuch 2>&1 | grep exists
Add stderr to stdout and ignore stdout:
ls -l exists nosuch 2>&1 1> /dev/null
Console will still show stderr. This form is often used to discard information about normal command execution from a script.
Combine all outputs and send to null:
ls -l exists.txt nosuch.txt &> /dev/null
The last example is often used to suppress all console output.
The "expr" command evalutes a string as an arithmetic expression:
expr 2 + 3
expr 12 / 4
expr 14 % 3
Note that expr requires spaces between operands and operators.
Parenthesis and "*" must be escaped:
expr 5 \* \(3 + 2\)
A somewhat neater way:
echo $[2*3+1]
Using the $[...] construct, nothing needs to be escaped.
The "let" command evalutaes the right side:
let a=4+6
This is equivalent to:
a=expr 4 + 6
Spaces are not allowed in "let" expressions.
Parenthesis must be escaped, but not "*":
let p=5*\(3+2\)
Again, it's easier to forget about the escapes and use:
let p=$[5*(3+2)]
Use "bc" for floating point computation
echo 45.3/2 | bc -l
The trailing -l (lower case L) loads the floating point library
x=`echo 99.0/3.14 | bc -l`
y=`echo 14.2 + 11 | bc -l`
echo $x + $y | bc -l
Base conversions
echo "obase=16; 1234" | bc
Select decimal places for result
echo "scale=3; 1/3" | bc
You don't need to use the -l if you set the scale > 0
echo "scale=3; 7/2" | bc
echo "scale=0; 7/2" | bc
Show how long a bc calculation takes (p to 1000 places)
time echo "scale=1000; 4*a(1)" | bc -l -q
Leading zeros:
printf "%04d\n" 3
Hex printf "%x\n" 23
All the usual suspects...
An alias is a type of macro:
alias name='expression'
It is often used to "improve" shell commands. For example, to make the rm command ask for confirmation:
alias rm="rm -i"
By convention, aliases are defined in a hidden file in the users home directory named ".bashrc".
You can display an alias defintion using:
alias myName
To remove an alias:
unalias name
Variables defined inside a shell script are only visible inside that script unless they are exported.
Exporting a variable makes it visible to external scripts called from inside the parent script.
To export one or more variables:
export var1 ... varn
Assignment and export can be combined:
export var1=expression1 ... varn=expressionN
When a parent script call a sub-script, variables exported by the sub-script are not visible in the parent. The parent can make them visible by using the "source" command:
source myScript.sh
There is a commonly used shorthand for this:
. myScript.sh
Note the space after the dot.
For example if you edit your login script ".bash_profile" and add some exported variables, you can make them visible (without loging out and back in) by executing:
source .bash_profile
Adding these lines at the beginning of a script will cause it to exit if any subsequent command fails:
set -o errexit
set -o pipefail
set -o nounset
Trying to mount a filesystem that's already mounted will throw an error in your your bash script. It's surprising there's no predicate to detect this, but you can use this construct instead:
if [ -z "$(findmnt $myPath)" ] ; then
mount $myPath
fi
ls # Show current directory contents
ls -l $path # Show details about the file or directory
ls -d $path # List directory names instead of contents
cd $dir # Change current directory to $dir
cd .. # Change current directory to parent directory
pwd # Show current directory path
mkdir $dir # Create a directory
cp $src(s) $dst # Copy $src file(s) to $dst
cp $src(s) $dir # Copy $src file(s) into the directory $dir
mv $src $dst # Move $src to $dst. Also used to rename files.
mv $src(s) $dir # Move a group of files into a directory
rm $file(s) # Remove (delete) files
rmdir $dir(s) # Delete empty directory(s)
rm -rf $dirs(s) # Delete files and/or directory(s) with their contents
> $file # Erase the contents of a file
touch $newFile # Create a new empty file
touch $oldFile # Change the modification time to "now"
touch -t YYMMDDhhmm $path # Change the modification time
Send the output of commandA to commandB:
commandA | commandB
Send the output (stdout) of commandA to a file:
commandA > somefilePath
Concatenate the output of commandA onto the end of a file:
commandA >> somefilepath
Splitting up and combining command output
commandA X optionalFilePath
Where X is:
1> Only stdout
2> Only stderr
&> Combine stdout and stderr
The "&>" is often, but not always, the default behavior of a command.
When using mass move, parameters must be quoted to avoid collision with the usual interpretation of wild cards. Each "*" on the source side corresponds to "#n" on the destination side where n=1 is the first "*" value, etc.
Examples:
mmv "*.old" "#1.new" # Change file extensions
mmv -a "*.txt" "all.txt" # Append files into one
cp -a $sourceDir $destDir
rsync -a --delete $sourceDir $destDir
rsync -aP $source $dest
chown owner file # owner only
chown owner.group file # owner & group
chown .group file # group only
chown owner. file # owner & group=owner
chmod changes fileName
The changes are a comma separated list of expressions. Each expression is of the form:
users+permissions # Add permissions
users-permissions # Remove permissions
users=permissions # Set exactly these permissions
The users can be one or more of the letters:
u User (Oner of the file)
g Group (Group of users)
o Others (Everyone else)
OR:
a All (Same as "ugo", the default)
The permissions can be one or more of the letters:
r Read
w Write
x Execute
The user classes are specified in the order UserGroupOther, with three bits for each to enable or disable ReadWriteExecute.
Example:
chmod u+rwx,g+rw,o-rwx aFile
Numerical form: Use three binary integers for "ugo" and one bit each for "rwx":
chmod 760 aFile
Is the same as:
chmod u+rwx,g+rw-x,o-rwx aFile
Binary: 111 11 0 000
Decimal: 7 6 0
du -s <dir>
du -sBG -t 1G *
echo anything
echo anything > <path>
echo anything >> <path>
touch <path>
> <path>
diff -r leftDir rightDir
diff -r -q leftDir rightDir
sh -x <fileName>
tail -f <fileName>
ln -s fileName linkName
ls --color=tty
(Alias this to ls)
ls -1
find -type d -maxdepth 1
(Alias this to lsd)
ls -lrt
ls -lrS
lsof
ls -1 | wc -l
du -ch -- **/*.jpg | tail -n 1
source .bash_profile (or whatever script you changed)
chroot newroot command
sh -x yourScript
The dd command can copy between files or devices.
dd if=sourcePath of=destPath bs=1M
Using the optional bs=n option can speed up the copy. You can use the suffix K, M, or G on numbers.
By adding the count option, you can write an exact number of fixed-size records. For example, to destroy the partition table of a disk:
dd if=/dev/zero of=/dev/sdb3 bs=1K count=1
To display the status of a dd copy that's aready started, use this command in another shell window:
kill -USR1 `pgrep '^dd$'`
This will cause dd to show a status message in it's original window and continue with the copy operation.
Use this script:
./zenter.sh path-to-chroot-files
The script:
#!/bin/bash
# zenter.sh - Mount system directories and enter a chroot
target=$1
mount -t proc proc $target/proc
mount -t sysfs sys $target/sys
mount -o bind /dev $target/dev
mount -o bind /dev/pts $target/dev/pts
chroot $target /bin/env -i \
HOME=/root TERM="$TERM" PS1='[\u@chroot \W]\$ ' \
PATH=/bin:/usr/bin:/sbin:/usr/sbin:/bin \
/bin/bash --login
echo "Exiting chroot environment..."
umount $target/dev/pts
umount $target/dev/
umount $target/sys/
umount $target/proc/
When you're finished inside, simply type "exit" and everything is restored to the normal state.
To update the /boot/initramfs image for the running kernel:
dracut -fv
To update some other kernel
dracut -fv --kver 5.2.7-100.fc29.x86_64
The kver name is in the form you see when you run:
uname -r
Fedora makes this a trial by packing the .img file with glark at both ends.
dnf install binwalk
myrd=/boot/initramfs-5.2.13-200.fc30.x86_64.img
binwalk $myrd
Take note of the decimal offset for the "gzip compressed data" near the end of the binwalk listing. For this example, it turned out to be 15360. Now proceed:
dd if=$myrd of=myrd.gz bs=15360 skip=1
gunzip myrd.gz
mkdir result
cd result
cpio -mid -H newc --no-absolute-filenames < ../myrd
You now have the initramfs in the result directory.
The systemd collection has a mechanism for patching or replacing service files with editing the original file directly. This is nice because it allows you to mess with things in a way that won't be undone by future updates to the package that provided the service. Unfortuately, dracut won't include such fixes in the initramfs.
When you make an incremental change using an expression like:
systemctl edit mything.service
A directory and file are created here:
/etc/systemd/system/mything.service.d/override.conf
This file contains whatever you typed in the editing session.
To make dracut include the fix, create this file:
/etc/dracut.conf.d/mything.conf
(The name doesn't actually matter as long as it ends with .conf)
That contains:
install_items+="/etc/systemd/system/mything.service.d/override.conf"
Your next dracut invocation will include the patch.
If you use the --full option when creating a patch, the new version of the service file is placed in the directory /etc/systemd/system. To make dracut include this file, use:
install_items+="/etc/systemd/system/mything.service"
The primary tool described in the following sections is "cdrecord". The most current versions of this program accept normal Linux CD device names, e.g. "/dev/cdrom" and support both SCSI and ATAPI drives.
Earlier versions of cdrecord only worked with SCSI drives and required the bizarre "x,y,z" drive name notation.
nice --18 mkisofs -l -J -r -V MyVolumeName sourceDirectory/ \
| cdrecord speed=x dev=/dev/cdrom -data -
To make a CDRW, add blank=fast to cdrecord options. Speed should be 8 for CDRs and 4 for CDRW on my HP 9200.
growisofs -dvd-compat -Z /dev/hdc -J -r /path/to/directory
growisofs -dvd-video -Z /dev/hdc /pathTo/Directory
The Directory should contain the AUDIO_TS and VIDEO_TS subdirectories expected on a video.
mkisofs -l -r -J -V MyVolumeName -o myISOfile.iso.bin sourceDirectory/
dvd+rw-mediainfo /dev/hdc
cdrecord -v dev=/dev/cdrom speed=2 -isosize /dev/cdrom
mpg123 -s file1.mp3 \
| cdrecord speed=x dev=/dev/cdrom -audio -pad -swab -nofix -
Use this command for each track, then fixate using the command documented next:
cdrecord dev=/dev/cdrom -fix
cdparanoia [-d device] trackRange result.wav
One wav per track:
cdparanoia 1- -B
cdparanoia trackNumber - | lame -b 160 - result.mp3
One wav per track:
cdrecord speed=s dev=/dev/cdrom -audio *.wav
1- # Entire CD
-- -3 # Beginning through track 3
2-4 # Tracks 2 through 4
cdrecord speed=4 dev=/dev/cdrom -data imageFile.iso.bin
For cdrw, add: blank=fast
cdrecord speed=4 dev=/dev/cdrom -isosize -dao -data /dev/hda2
For cdrw, add: blank=fast
readcd dev=/dev/cdrom f=myImageFile.iso.bin
Older versions of cdrecord require scsi drivers or scsi emulation with atapi drives. The following sections show how to deal with this situation.
The cdrecord program wants to see scsi devices: The cdrom module must be loaded first, but it will normally be loaded if it was operating in ide mode. Otherwise, do an "insmod cdrom" first.
rmmod ide-cd
insmod cdrom
insmod sr_mod
insmod ide-scsi
The scsi-mod will be loaded if you have a real scsi interface in your machine. Otherwise, # it must be loaded before sr_mod.
rmmod sr_mod ide-scsi
insmod ide-cd
For this example, assume you have two ide drives:
hdc and hdd.
Method 1: Add this line to you kernel boot options:
append="hdc=ide-scsi hdd=ide-scsi"
Method 2: Add these lines to /etc/modules.conf:
options ide-cd ignore=hdc
options ide-cd ignore=hdd
pre-install sg modprobe ide-scsi
pre-install sr_mod modprobe ide-scsi
pre-install ide-scsi modprobe ide-cd
/dev/scd0 cdram
/dev/scd1 cdrom
/dev/scd1 dvd
/dev/hdc cdram
/dev/hdd cdrom
/dev/hdd dvd
The cdrecord program will use "dev=x,y,z" notation where x,y,z are shown by the command:
cdrecord -scanbus
/boot/* # Linux kernel and initrd files
/etc/aliases # Redirect mail
/etc/auto.mount # Autofs mountpoints
/etc/dhcp/dhcpd.conf # Specify DHCP names and numbers
/etc/exports # NFS shares
/etc/named.conf # DNS configuration
/etc/fstab # Boot time mountpoints
/etc/hosts # Define hostnames and ip numbers
/etc/httpd/conf.d/*.conf # Apache configuration files
/etc/mail/sendmail.mc # Sendmail configuration macros
/etc/mail/local-host-names # Mail domains handled by this server
/etc/modprobe.d/* # Modify kernel module parameters
/etc/php.ini # PHP global settings
/etc/profile.d/* # Shared environment variables
/etc/resolv.conf # Specify IP name server
/etc/samba/smb.conf # Samba shares
/etc/selinux/config # Where to turn off selinux
/etc/ssh/ssh_host_rsa_key . # Host private RSA key
/etc/ssh/ssh_host_rsa_key.pub . # Host public RSA key
/etc/sudoers # Users allowed to "sudo"
/etc/sysconfig/network # Specify IP gateway
/etc/sysconfig/network-scripts # "ifcfg" scripts for network adapters
/etc/sysctl.d/* # Boot time kernel parameter settings
/var/named # DNS zone files
/var/spool/mail # User inboxes
~/.bashrc # Per-user bash customization
~/.procmailrc # Per-user procmail filters
~/.ssh/authorized_keys # Per-user authorized keys
~/.ssh/known_hosts # Per-user RSA known hosts
~/.ssh/id_rsa # Per-user private RSA key
~/.ssh/id_rsa.pub # Per-user public RSA key
# Root and swap volumes
/dev/hda1 / ext3 defaults 1 1
/dev/hda3 swap swap defaults 0 0
# Special device mounts
none /proc proc defaults 0 0
none /dev/pts devpts gid=5,mode=620 0 0
none /dev/shm tmpfs defaults 0 0
# Removable media
/dev/fd0 /mnt/floppy auto noauto,owner 0 0
/dev/cdrom /mnt/cdrom iso9660 noauto,owner,ro 0 0
# Logical volumes on the boot device
/dev/vg2/spoolVol /var/spool ext2 defaults 0 0
/dev/vg2/homeVol /home ext2 defaults 0 0
/dev/vg2/wwwVol /var/www ext2 defaults 0 0
# Logical volumes on the backup device
/dev/vg1/backVol /mnt/back ext3 defaults 0 0
/dev/vg1/archVol /mnt/dos ext3 defaults 0 0
# Samba network
//hp/dos /mnt/hpDos cifs noauto,username=administrator 0 0
//hp/c /mnt/hpWin cifs noauto,username=administrator 0 0
//sparksVaio/C$ /mnt/vaio cifs noauto,username=administrator 0 0
//sparks9k/Main /mnt/9kWin cifs noauto,username=administrator 0 0
# NFS network
# hp:/mnt/c /mnt/dummy1 nfs noauto,_netdev 0 0
# Loop mount example
# /mnt/Mac.hfs /mnt/mac hfs noauto,loop 0 0
/mnt/back *.csparks.com(rw,no_root_squash)
/mnt/dos *.csparks.com(rw,no_root_squash)
/var/www/html *.csparks.com(rw,no_root_squash)
/mnt/thing 192.168.1.0/24(rw,no_root_squash)
For non-EFI systems, there is a symbolic link:
/etc/grub2.cfg -> /boot/grub2/grub.cfg
For EFI systems, the configuration file is:
/boot/efi/EFI/fedora/grub.cfg
Here is a typical menu entry:
menuentry 'Fedora (4.18.13-100.fc27.x86_64)' ... {
load_video
set gfxpayload=keep
insmod gzio
insmod part_gpt
set root='hd0,gpt2'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy <lots of places>
else
search --no-floppy --fs-uuid --set=root f29f6832999194c6
fi
linuxefi /fedora@/boot/vmlinuz-4.18.13-100.fc27.x86_64 ro rhgb quiet
initrdefi /fedora@/boot/initramfs-4.18.13-100.fc27.x86_64.img
}
When a device is started, the static-routes file is read by the script ifup-routes. For each line that matches the device in the first parameter it reads the line:
read device args
The routes are added by a script that performs "route add" (Note the minus character before $args)
route add -$args $device
For example: (This is used to route back to basilisk)
eth0 host 192.168.2.3 gw 192.168.0.1
openssl list-cipher-commands
openssl des3 -salt -in mydoc.txt -out mydoc.txt.des3
openssl des3 -d -salt -in mydoc.txt.des3 -out mydoc.txt
The davfs filesystem allows you to treat remote webdav shares like regular mountpoints.
Install the package:
dnf install davfs2
That will create a file:
/etc/davfs2/secrets
Edit this file, adding a line for each of your remote shares:
https://someServer.com/someShare remoteUserName remotePassword
For example a Nextcloud share looks like this:
https://someServer.com/remote.php/webdav remoteUserName remotePassword
Now you can mount the share from the command line:
mkdir myStuff
mount -t davfs https://someServer.com/someShare myStuff
Or in fstab:
https://someServer.com/someShare /mnt/myStuff davfs rw,noauto 0 0
Or with autofs, in /etc/auto.mount:
myStuff -fstype=davfs :https\://someServer.com/someShare
Note that you must escape the URL ":" in the auto.mount file.
# Shared
ddns-update-style none ;
option ###domain-name "csparks.com" ;
option domain-name-servers 192.168.1.2 ;
log-facility local1;
subnet 192.168.0.0 netmask 255.255.255.0
{ authoritative ;
}
subnet 192.168.1.0 netmask 255.255.255.0
{ option routers 192.168.1.2 ;
option subnet-mask 255.255.255.0 ;
option broadcast-address 192.168.1.255 ;
option domain-name "csparks.com" ;
option domain-name-servers 192.168.1.2 ;
pool
{ range 192.168.1.100 192.168.1.200 ;
}
authoritative;
}
# Fixed
host sparksc2
{ hardware ethernet 00:16:36:a5:fe:fb ;
fixed-address 192.168.1.3;
}
host sparksc2w
{ hardware ethernet 00:18:de:5b:50:c6 ;
fixed-address 192.168.1.3;
}
host cgsVaio
{ hardware ethernet 00:01:4a:16:b6:58;
fixed-address 192.168.1.5;
}
All hardware:
lshw
Display hardware summary:
lshw -short
Display hardware of a selected class:
lshw -class <name>
Class names:
memory
disk
network
processor
bridge
display
bus
volume
Examples:
lshw -short -class processor
Display hardware with a GUI:
lshw-gtk
List CPU information
lscpu
List PCI devices
lspci
List USB controllers
lsusb
List block devices
lsblk
System:
dmidecode -t system
Memory:
dmidecode -t memory
Processor:
dmidecode -t processor
BIOS:
dmidecode -t bios
To get the best effect, you first have to scan your hardware:
sensors-detect
To see everything:
sensors
To monitor continuously every second:
watch -n 1 sensors
fdisk -l
fdisk /dev/devname
blkid /dev/sda1
hdparm options /dev/sda
With no options, displays brief drive information. There are dozens of options to control low-level device features. Most of these are already optimized by default and can be dangerous to manipulate. The most common use of hdparm is for setting and displaying power saving features.
-I Display extended drive information.
-S n Spindown after n 5 sec tics (0 <= n <= 240)
-B Display the state of advanced power saving features.
-B 1..127
Enable advanced power saving features including spindown.
1: Max power saving. 127: Min power saving.
-B 128..255
Enable advanced power saving without spindown.
128: Max power saving. 255: Disable power saving.
-y Go to low power state (usually includes spindown)
-Y Go to lowest power state. (requires reset)
-C Show the current power saving state:
active/idle, standby, sleeping
-t Perform & display drive speed test results.
For these examples, the device is /dev/sdX.
For luck, tail the journal in a separate shell window:
journalctl -f -t kernel
Unmount file systems that use the device:
It depends. You have to know...
Sleep:
hdparm -Y /dev/sdX
Remove from kernel:
echo 1 > /sys/block/sdX/device/delete
Attach a new disk:
Plug it in. I like to attach the power cable first,
wait a bit, and then attach the SATA connector.
If it's an ATA controlled device, it will be recognized
and attached. If not, you can try a re-scan:
Scan for new devices:
exec tee /sys/class/scsi_host/host*/scan <<<'- - -' >/dev/null
DNF is the successor to Yum.
dnf install <packageName>
dnf remove <packageName>
dnf list installed
dnf group list
dnf group install <groupName>
dnf list <partial package name>*
dnf info <packageName>
dnf repolist
dnf update
dnf config-manager --add https://server.csparks.com/rpms
dnf config-manager --save --setopts=server.csparks.com_rpms.gpgcheck=0
I find that "things go better with DNS". This applies to lots of programs including MySQL and sendmail.
I host my own domain and 2 or 3 others without having external secondary servers. This causes the angels to weep. But even if you just keep a local LAN, runnng DNS is convenient. If you don't host externally visible domains, proceed as shown below but leave out the external view in /etc/named.conf.
The following sections show samples of each configuration file. The zone files "*.zone" and "*.rev" contain a serial number that must change each time you edit the file.
Tell named to reload the configuration after changes:
rndc reload
If you try to use systemctl restart named, you will get an error because the socket is in use.
multi on
order hosts,bind
search csparks.com
nameserver 127.0.0.1
127.0.0.1 localhost localhost.localdomain
NETWORKING=yes
HOSTNAME=server
GATEWAY=192.168.0.254
acl "mynet" { 127/8; 192.168.1.0/24; } ;
options {
listen-on port 53 { any; };
// listen-on-v6 port 53 { ::1; }; // Hugh
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
secroots-file "/var/named/data/named.secroots";
recursing-file "/var/named/data/named.recursing";
allow-transfer { none; };
allow-notify { none; };
version "unknown" ;
dnssec-enable yes;
dnssec-validation yes;
managed-keys-directory "/var/named/dynamic";
geoip-directory "/usr/share/GeoIP";
pid-file "/run/named/named.pid";
session-keyfile "/run/named/session.key";
include "/etc/crypto-policies/back-ends/bind.config";
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
include "/etc/named.root.key";
view "internal"{
match-clients { mynet; };
recursion yes;
allow-query { mynet; };
allow-query-cache { mynet; };
allow-recursion { 127.0.0.1; mynet; };
match-recursive-only yes ;
zone "." IN {
type hint;
file "named.ca";
};
include "/etc/named.rfc1912.zones";
zone "csparks.com" {
type master;
file "csparks.internal.zone";
};
zone "1.168.192.in-addr.arpa" {
type master;
file "csparks.internal.rev";
};
zone "popularmaniacs.com" {
type master;
file "popularmaniacs.internal.zone";
};
}; // end of internal view
view "external"{
match-clients { any; };
recursion no;
allow-query { any; };
allow-recursion { none; };
match-recursive-only no ;
zone "." IN {
type hint;
file "/var/named/named.ca";
};
zone "csparks.com" {
type master ;
file "csparks.external.zone" ;
allow-transfer { 69.65.50.192 ; };
also-notify { 69.65.50.192 ; };
};
zone "popularmaniacs.com" {
type master ;
file "popularmaniacs.external.zone" ;
};
}; // end of external view
zone "localhost.localdomain" IN {
type master;
file "named.localhost";
allow-update { none; };
};
zone "localhost" IN {
type master;
file "named.localhost";
allow-update { none; };
};
zone "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa" IN {
type master;
file "named.loopback";
allow-update { none; };
};
zone "1.0.0.127.in-addr.arpa" IN {
type master;
file "named.loopback";
allow-update { none; };
};
zone "0.in-addr.arpa" IN {
type master;
file "named.empty";
allow-update { none; };
};
$TTL 3D
@ IN SOA dns1.csparks.com. root.csparks.com. (
2010040701 ; serial: todays date + todays serial
8H ; refresh, seconds
2H ; retry, seconds
4W ; expire, seconds
1D ) ; minimum, seconds
NS 192.168.1.2.
NS 192.168.1.2.
MX 10 mail.csparks.com.
MX 20 mx1.mc.mpls.visi.com.
A 192.168.1.2
server A 192.168.1.2
mail A 192.168.1.2
dns1 A 192.168.1.2
dns2 A 192.168.1.2
another A 192.168.1.3
...
ftp CNAME server
www CNAME server
shell CNAME server
...
$TTL 3D
@ IN SOA server.csparks.com. root.csparks.com. (
2010040701 ; Serial, todays date + todays serial
8H ; Refresh
2H ; Retry
4W ; Expire
1D) ; Minimum TTL
NS server.csparks.com.
2 PTR server.csparks.com.
3 PTR another.csparks.com.
...
Multiline text body:
mail -s 'A subject string' someone@somewhere.com
Type your message here
and end with a <control>d
One line:
echo "This is a one line message" | mail -s 'A subject string' someone@somewhere.com
Message from a file:
cat messageBody.txt | mail -s 'A subject string' someone@somewhere.com
echo "See enclosed document" | mutt -s 'A subject string' -a 'myFile.bin' -- someone@somewhere.com
You can add the message body text by any means shown in the previous section for the "mail" command.
This will create a minimal message:
telnet destination.email.server 25
ehlo sender.com
mail from: senderName@sender.com
rcpt to: recipientName@destination.com
data
Your message text goes here on one
or more lines. The last line must be a period:
.
quit
This will create a message with all standard fields:
telnet destination.email.server 25
ehlo sender.com
mail from: senderName@sender.com
rcpt to: recipientName@destination.com
data
To: Recipient Display Name <recipientName@destination.com>
From: Sender Display Name <senderName@sender.com>
Subject: This is a test
Type your message here and end with a dot:
.
quit
Note that two
telnet <destinationMachine> 110
USER <yourEmailAddress>
PASS <yourPassword>
STAT
RETR n
DELE n
QUIT
telnet <destinationMachine> 143
a login <yourUsername> <yourPassword>
a select inbox
a fetch <n> full
a fetch <n> body[header]
a fetch <n> body[text]
a logout
sendmail -bp
OR
mailq
This is only useful if your machine will act as a mail server for your domain. It is not necessary if you send and receive email via an ISP. This is not an adequate recipe if you intend to host mulitple domains.
Changes for /etc/sendmail.mc
Enable listening on the external smtp port
dnl DAEMON_OPTIONS(Port=smtp,Addr=127.0.0.1, Name=MTA)dnl
Masquerade changes header fields on outgoing mail so they alway appear to come from username@yourdomain.com rather than from whatever machine on your internal LAN was the source. That's almost always what you want to to:
MASQUERADE_AS(`yourdomain.com')dnl
MASQUERADE_DOMAIN(`yourdomain.com')dnl
FEATURE(`masquerade_envelope')dnl
FEATURE(`masquerade_entire_domain')dnl
If-and-only-if you don't have DNS (bind) configured, you need to explicity tell sendmail your server's host name. This should match the whatever an external reverse-lookup of your IP address returns. If the names don't agree, some remote servers may reject mail from your domain.
define(`confDOMAIN_NAME', `yourserver.yourdomain.com')dnl
After changing /etc/mail/sendmail.mc you need to run the macro processor:
m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
Note: On Fedora systems, you can rebuild sendmail.cf and any modified database files by simply running "make" in the sendmail directory.
Enable relaying for your domain in /etc/mail/access. This allows other machines on your LAN to send mail through the server to other destinations:
Connect:localhost.localdomain RELAY
Connect:localhost RELAY
Connect:127.0.0.1 RELAY
annoying.ru 550 You are a poltroon
yourdomain.com RELAY
Rebuild the database (access.db)
makemap hash /etc/mail/access < /etc/mail/access
Populate local-host-names with all domain names and host names sendmail will accept as mail recipiants: The name of your server "server.yourdomain.com" should match the name you specified for the MX record when you registered your domain name.
yourdomain.com
server.yourdomain.com
mail.yourdomain.com
If you have linux client machines running on your internal LAN that will send mail via your server, they need to have the "dotted" name of the mail server in their /etc/hosts file. (This is not necessary if you are running a properly configured DNS server.) Note the trailing dot:
192.168.0.2 mail.yourdomain.com.
Enable the sendmail daemon at boot time:
chkconfig --add sendmail
Restart the server after making changes:
service sendmail restart
sendmail -bp
Or simply:
mailq
The /etc/virtusertable is used to reroute mail. The left column has addresses for domains or email addresses accepted by your server. (You listed them in local-host-names.) The right column has the destination where the mail will be sent:
root@yourdomain.com yourname@yourdomain.com
admin@yourdomain.com yourname@yourdomain.com
You can also send the same message to multiple destinations:
exuser@yourdomain.com responder@yourdomain.com
exuser@yourdomain.com exuser@somewhere_else.com
This is a catch-all entry for yourdomain.com:
@yourdomain.com satan@hell.org
You can also send mail to the same user on a different domain:
@otherdomain.com %1@somewhere.com
In the example above, the %1 matches the username on mail directed to otherdomain.com.
The /etc/aliases file redirects mail accepted for local delivery. It is used after the virtusertable does its thing. It has a similar format, but note the required colons:
root: yourname
postmaster: yourname
happylist: yourname,bill,jane,walter,golum@mordor.com
Note that the last line implements a simple mailing list. The last member is on a remote machine.
Note: The "postmaster" is a required user on a domain that conforms to the email RFCs. If you discard mail not directed to known local users in virtusertable, you should first match and redirect postmaster@yourdomain.com in that file because it will never make it to the aliases redirect.
Entry for /etc/xinetd.d
service imap
{ socket_type = stream
wait = no
user = root
server = /usr/sbin/imapd
disable = no
}
Create an md5 password file owned by root:
touch /etc/cram-md5.pwd
Add one line for each imap user of this form:
username<tab>password
Both pop & imap will use this file to avoid transmitting clear-text passwords.
After editing, the file permissions should be changed:
chmod a-rwx,o+r /etc/cram-md5.pwd
Edit /etc/aliases and add:
mything-users: yourname,localuser1,localuser2,golum@mordor.com
If the member list gets too long, you can put them in a file:
mything-users: :include/home/lists/mything-users
In the file /home/lists/mything-users:
yourname
localuser1
localuser2
golum@mordor.com
Permissions:
755 /home/lists
644 /home/lists/mything-users
It's best to convince list users to add a prefix to their subject lines:
[mything-users] Whatever
This example assumes you have installed a redhat/fedora mailman rpm.
Edit: /usr/lib/mailman/Mailman/mm_cfg.py
Modify these definitions:
DEFAULT_URL_HOST = 'www.yourdomain.com'
DEFAULT_EMAIL_HOST = 'yourdomain.com'
Create the "mailman" mailing list:
cd /usr/lib/mailman
./bin/newlist mailman
You will be asked to provide your email address and a password. A list of alias definitions are presented and you must copy these into:
/etc/aliases
Then run:
newaliases
Provide a site password by running:
cd /usr/bin/mailman
./bin/mmsitepass
Configure the system service
chkconfig mailman on
service mailman start
Edit the httpd configuration file in:
/etc/httpd/conf.d/mailman
Un-comment and edit the line at the end to redirect mailman queries on your server, then restart httpd:
service httpd restart
Now you can visit
http://www.yourdomain.com/mailman
Check your own email and you should see the creation announcement for the new list "mailman."
To create new lists:
cd /usr/lib/mailman
./bin/newlist mynewlist
To delete a list
cd /usr/lib/mailman
./bin/rmlist listname
To remove all the associated archives as well:
./bin/rmlist -a listname
fdformat /dev/fd0H1440
mkfs -t msdos /dev/fd0H1440 1440
When putting ext2 on a floppy, omit the su reserve:
mkfs -t ext2 -m 0 /dev/fd0H1440 1440
Some-but-not-all floppies can be enlarged:
fdformat /dev/fd0u1722
mount -t iso9660 -ro /dev/hdc /mnt/cdrom
mount -t vfat /dev/hda5 /mnt/dos
mount -t ext2 /dev/sda3 /mnt/jazz
mount -t ntfs /dev/hda1 /mnt/nt
mount -t cifs //sparks750/c /mnt/sparks750
mount -t cifs //qosmio/c$ /mnt/qosmio -o username=ann,password=nelly
(See fstab below for more cifs options)
mount -t hfs /dev/sda /mnt/jazz -o afpd -o uid=500
(Currently, the afpd option hangs up the Mac...)
mount -t nfs mac.sparks.com:/root /mnt/macroot
To support nfs mounts, remote system must have /etc/exports: /root *.sparks.com(rw)
Mounting labeled devices: e2fs and vfat partitions may be assigned labels.
To use a label:
mount -t ext3 -L mylabel /mnt/stuff
Newer versions of Linux figure out the filesystem type automatically so the -t options can often be omitted.
e2label /dev/sdb3 mylabel
There is no simple tool like e2label for vfat partitions. First, you must mount the partition the old way. For this example, we assume it's /dev/sda3.
mount -t vfat /dev/sda3 ~/here
Now add a line in /etc/mtools.conf:
drive x: file="/dev/sda3"
Assign the partition a new label:
mtools x:MYLABEL
Display the label:
mtools -s x:
You can remove the line added to /etc/mtools.conf and unmount the partition:
umount ~/here
From now on, you can mount it using the label:
mount -t vfact -L MYLABEL ~/here
Or with a line in /etc/fstab:
LABEL=MYLABEL /mnt/myThing vfat defaults 0 2
This is especially nice for USB memory sticks because they will be associated with different devices depending on their mount order.
dd if=/dev/zero of=MyDiskImage.ext2 bs=1k count=1000
mkfs -t ext2 MyDiskImage.ext2
mkdir here
mount -t ext2 -o loop MyDiskImage.ext2 here
Show all active (in use) loop devices:
losetup -a
Show the first available loop device:
losetup -f
Attach a loop device to a file:
losetup /dev/loop0 MyDiskImage.ext2
Mount the device with a specified filesystem:
mount -t ext2 /dev/loop0 here
This does the same thing as mount with the -o option. It is easier to use the -o option because you don't have to deal with finding and specifying a free loop device.
When you are finished, unmount the volume:
umount here
And free the loop device:
losetup -d /dev/loop0
dd if=/dev/zero of=MacDiskImage.hfs bs=1k count=whatever
hformat -l "HD1" MacDiskImage.hfs
e2fsck -cfpv
-c Check for bad blocks and put them on the "don't use" list
-f Force checking even if filesystem is "clean"
-p Perform automatic fileystem repairs
-v Verbose mode
df -h
The -h option selects human-readable units.
du -sh -- */ | sort -rh
tune2fs -l /dev/hdax
mkfs -t ext2 -j /dev/hdax
tune2fs -j /dev/hdax
Revert from ext3 to ext2 if necessary (see below) I have heard that this step is unnecessary.
unmount /dev/hda1
e2fsck -f /dev/hda1
resize2fs /dev/hda1 newSizeInBlocks
mount /dev/hda1 /mnt/point
If newSize is not specified, the file system will grow to fill the partition.
After shrinking a file system, you can shrink the partition to match.
After growing a partition, you can grow the file system to match.
umount /dev/hda1 # Unmount the partition
tune2fs -O ^has_journal /dev/hda1 # Turn off journaling
e2fsk -y /dev/hda1 # Check for errors
mount -t ext2 /dev/hda1 /mnt/point # Remount as ext2
cd /mnt/point # Go to root directory
rm -f .journal # Remove the journal
You must update entry in fstab if this is a permanent change.
Ext3 should be reverted to ext2 before resizing.
tune2fs -j /dev/hda1
Edit fstab to indicate ext3.
If this is the root partition, you need to use an initrd to boot.
See redhat documentation for details.
This is the new and prefered way to handle file system encryption. See the next section on the older default method.
Create a zvol named "temp2"
zfs create zool/temp2 -V 32G
Randomize it: (optional, very slow, more secure)
badblocks -c 10240 -s -w -t random -v /dev/zool/temp2
Format with luks
cryptsetup create luksFormat /dev/zool/temp2
Mounting the encrypted volume
cryptsetup luksOpen /dev/zool/temp2 goom
The previous command creates a device node named "goom":
/dev/mapper/goom
Format the volume
mkfs -t ext4 /dev/mapper/goom
Mount the filesystem
mount /dev/mapper/goop ~/here
To close down everything:
umount ~/here
cryptsetup remove goom
Create OR mount an existing encrypted device
cryptsetup create gark /dev/zool/temp2
The previous command will also mount gark here:
/dev/mapper/gark
Format the volume
mkfs -t ext4 /dev/mapper/gark
Mount the filesystem
mount /dev/mapper/gark here
Close
umount here
cryptsetup remove gark
Configure autofs and you'll never have to type mount commands again!
The autofs service must be running for this to work.
service autofs status
If autofs was not running, you can start it using:
service autofs start
Configure autofs to start after reboot:
chkconfig autofs on
Configuration files
The master file specifies one or more directores where mount points will be automatically created and the files that contain the items to be mounted.
/etc/auto.master
/mnt /etc/auto.mount
/goop /etc/auto.goop
Each mount point file contains any number lines of the form:
mount-point-name -fstype=filesystem,options :device
An example:
/etc/auto.mount
dvd -fstype=iso9660,ro,nosuid,nodev :/dev/cdrom
stick -fstype=auto :/dev/sdb1
floppy -fstype=auto :/dev/fd0
asus -fstype=cifs,rw,noperm,username=xxxx,password=yyyy ://asus/mydir
After editing these files, you must reload:
service autofs reload
You can now access the contents of these directories by simply using them:
ls /mnt/stick
cd /mnt/asus
...
The autofs deamon will unmount these resources when they are unused for a specified time. This timeout can be configured in:
/etc/sysconfig/autofs
The timeout is specified in seconds using this expression:
TIMEOUT=300
See also IPTables
Open for a service:
firewall-cmd --add-service=samba
firewall-cmd --remove-service=samba
Remove a service
firewall-cmd --remove-service=<name>
List open services
firewall-cmd --list-services
List all possible service names
firewall-cmd --get-services
Open a port:
firewall-cmd --add-port=port/proto
firewall-cmd --remove-port=port/proto
Open a UDP port (ethercat)
firewall-cmd --add-port=34980/udp
Open a range of ports
firewall-cmd --add-port=8000-8100/tcp
Close a port
firewall-cmd --remove-port=<number>
List open ports:
firewall-cmd --list-ports
Protocol values:
tcp, udp, (others)
Non-permanent channges take effect immediately.
Make changes permanent by adding:
--permanent
After making a permanent change:
firewall-cmd --reload
You can make all non-permanent changes permanent using:
firewall-cmd --runtime-to-permanent
Go in/out of panic mode
firewall-cmd --panic-on
firewall-cmd --panic-off
modprobe ieee1394
modprobe ohci1394
The ohci module will recognize your disk as a SCSI device and automatically load the serial bus protocol (sbp2) module.
If you need to see what's going on for debugging, do a tail -f /var/log/messages in another shell window before you load the module.
cdrecord --scanbus
Mine was at SCSI addresss 2,0,0 so it is /dev/sdb.
If the result had been 1,x,y it would be on /dev/sda.
fdisk /dev/sdb
I found the DOS partition on the ipod at /dev/sdb2
mkdir /mnt/ipod
mount -t vfat /dev/sb2 /mnt/ipod
/dev/sb2 /mnt/ipod vfat noauto 0 0
mount /mnt/ipod
umount /mnt/ipod
rmmod sbp2
After the rmmod, the iPod will tell you that it's ok to disconnect. This precaution should be observed before unplugging any firewire disk.
modprobe sbp2
mount /mnt/ipod
gdb <program> # Start gdb and select the program
file <program> # Specify or change the program in gdb
attach <pid> # Attach to a running process
quit # Exit debugger
cd # Change directories
pwd # Show working directory
edit <fileName> # Edit a file
run <p1...pn> # Start program with parameters
start <p1..pn> # Start program and break at main()
step # Step into
next # Step over
cont # Continue from break
jump <line> # Jump to <line>
finish # Finish this function and return to caller
return # Return now (skip rest of func)
return <expr> # Return now with this value
list <loc> # List source starting at location
list <l1>,<l2> # List source from l1 to l2
list # No <line> continues listing
directory path # Add a source file directory
frame # Show current execution context
frame <n> # Switch context to frame n
backtrace # Show all frames on the stack
up # Switch context up one frame
down # Swtich context down one frame
break <loc> # Set breakpoint
clear <loc> # Clear breakpoint
watch <expr> # Watch the value
delete <n> # Delete by number
disable <n> # Diabled by number
enable <n> # Enable by number
condition <n> <boolean expression>
display <expr> # Print value at each break
undisplay <n>
enable display <n>
disable display <n>
print <expr> # Show value of expression
print/x <expr> # Show value in hex
set <var> <expr> # Change the value of a variable
whatis <var> # Show the type of a variable
info breakpoints # Show breakpoint locations and numbers
info watchpoints # Show current watchpoints
info display # Show displays
info args # Show args of the context frame
info locals # Show local vars
info variables rx # Show global vars. Rx=regexp
info functions rx # Show functions. Rx=regexp
info threads # Show threads and process pid
info macro <name> # Show macro definition
234 # A line number
*$pc # The current execution location
myfun # A function
myFile.c:234 # A line in a source file
myFile.c:myfun # A function in a file
Programs that respond to high rate real-time events (SIG34) are difficult to debug without these steps:
In the user's home directory, create the file:
.gdbinit
With contents:
handle SIG34 nostop noprint pass
set print thread-events off # Stop annoying thread state messages
dll-symbols myThing.dll # Preload dll symbols
Attach the process:
strace -p procesId
Then issue
Set a breakpoint like this:
b OutputDebugStringA
When the error occurs, dump the stack:
frame
mogrify -resize 50% *.jpg
mogrify -resize 400 *.jpg
mogrify -colorspace gray *.jpg
mogrify -format jpg *.gif
mogrify -rotate 90 myfile.jpg
mogrify -rotate "90>" myfile.jpg
mogrify -rotate "90<" myfile.jpg
jhead -ft *.jpg
A staggering amount of disinformation exits on the web about configuring grub2. This due to differences between linux distributions as well as frequent changes to the grub2 package. When people write helpful tutorials like this one and then forget about them, the world deteriorates.
This section describes the correct procedure for UEFI firmware as of 2024-01-24. If you're reading this in the far future, these examples are probably incorrect.
METHOD 1: Passing kernel command line options with grubby
This appears to be the new standard way used by Fedora installers. In this case, you can do without this file entirely:
/etc/default/grub
Instead, each kernel command line parameter is set using "grubby".
Example: Blocking the nouveau driver when using proprietary nvidia drivers:
grubby --update-kernel=ALL --args="rd.driver.blacklist=nouveau"
grubby --update-kernel=ALL --args="modprobe.blacklist=nouveau"
grubby --update-kernel=ALL --args='nvidia-drm.modeset=1'
grubby --update-kernel=ALL --args="ibt=off"
Example: Get rid of selinux:
grubby --update-kernel=ALL --args="selinux=0"
Example: Turn off auditing:
grubby --update-kernel=ALL --args="audit=0"
Example: Booting with root file system on ZFS:
grubby --update-kernel=ALL --args="root=ZFS=zool/fedora"
In this example, "zool" the name of your rootfs pool
and "fedora" is the dataset name.
Removing a kernel command line parameter:
grubby --update-kernel=All --remove-args="audit"
METHOD 2: Using the /etc/default/grub file:
Edit: (or create)
/etc/default/grub
Inside, define (for example)
GRUB_CMDLINE_LINUX="rd.driver.blacklist=nouveau modprobe.blacklist=nouveau"
Now run:
grub2-mkconfig -o /etc/grub2-efi.cfg
This will update the BLS entries for all your kernels in:
/boot/loader/entries
Repairing a damaged grub configuration:
Before Fedora 34 and currently on many other grub2-based linux distributions, this command was used to update the boot file after editing /etc/default/grub:
grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg
This procedure is documented on countless websites.
After Fedora 33, the procedure changed:
grub2-mkconfig -o /etc/grub2-efi.cfg
The old grub.cfg file is now a short dispatcher script you should never change:
/boot/efi/EFI/fedora/grub.cfg
If you accidentally overwrote /boot/efi/EFI/fedora/grub.cfg by using grub2-mkconfig the old way, you can repair your installation:
Remove all existing grub.cfg files:
rm /boot/efi/EFI/fedora/grub.cfg
rm /boot/grub2/grub.cfg
Then reinstall grub:
dnf reinstall shim-* grub2-efi-* grub2-common
Addendum:
The exceptionally alert will notice that there are two symbolic links that point to the same file:
/etc/grub2-efi.cfg => ../boot/grub2/grub.cfg
/etc/grub.cfg => ../boot/grub2/grub.cfg
This is not a mistake. The magic will work.
To see all the hardware in your system as a formatted outline:
lshw
To see a shorter summary:
lshw -short
You can restrict the display using the -class name option:
lshw -class <name>
Commonly used class names:
generic
system
memory
processor
bridge
storage
disk
volume
communication
network
power
The options can be combined. Example:
lshw -short -class memory
This where the boot file system lives, packed into a file. Example:
/boot/initramfs-x.y.z-100.fc30.x86_64.img
A new img file is created whenever you update the kernel. This is usually done automatically by the "dnf update" process. To recreate the file by hand:
dracut -fv
If you need to create the img file for some other kernel version:
dracut -fv --kver <kernel version>
Where kernel version has the form:
5.5.9-100.fc30.x86_64
You can see the kernel version string for the running kernel using:
uname -r
To list the contents of the initramfs:
lsinitrd /boot/<any ramfs img file>
To unpack an initramfs file:
mkdir /tmp/initramfs
cd /tmp/initramfs
cp /boot/initramfs-x.y.z.img .
/usr/lib/dracut/skipcpio initramfs-x.y.z.img | zcat | cpio -ivd
Server motherboards often have dedicated LAN ports for remote console access. This lets you see and interact with the boot/BIOS process even on headless machines.
dnf install freeipmi
ipmiconsole -h hostIpmiAddress -u myUser -p myPassword
The hostIpmiAddress must be configured in the BIOS or have a known default before this will work. It's convenient to change it so it's on the same LAN as the host.
Other IPMI tools:
dnf install ipmitool
ipmitool chassis status
ipmitool sensor list
ipmitool sdr
ipmitool lan print
ipmitool shell
The ipmitool examples are for local access. To use them remotely, add:
-H hostIpmiAddress -U myUser -P myPassword ...
See also Firewall
Incoming and outgoing IP packets pass through chains. A chain is a list of rules. A rule specifies a pattern to match in an IP packet's header. If the rule does not match, the packet is passed on to the next rule in the chain. If the rule matches, the packet is passed to the target. The target of a rule can be another chain or one of the special targets: ACCEPT, DROP, QUEUE or RETURN.
ACCEPT - Let the packet through
DROP - Throw the packet away
RETURN - Leave this chain and let the caller decide.
QUEUE - Pass the packet to an external program.
There are built-in chains and user-defined chains. If packet 'runs off' the end of a user-defined chain without triggering a rule, RETURN is the default target. If a packet runs off the end of a built-in chain, a default target is selected. This target is configured by a command that sets the default chain policy.
Chains are organized into named tables. There are two commonly used tables: "filter" and "nat". Both of these tables have some built-in chains that are connected in a flow diagram. (A link to the diagram is in the next section.)
Chains have names local to their parent table. It convenient to think of the complete name of a chain as the concatenation of the table name and the chain name. (Different tables may use the same local chain names.)
When a packet arrives for processing by the firewall, its source and destination address are examined to determine which built-in filter chain should be used:
INPUT - Destination is on this machine.
OUTPUT - Source is on this machine, destination is elsewhere.
FORWARD - Source and destination are elsewhere.
The FORWARD chain is exclusive: packets that arrive from outside to be routed elsewhere do not pass through the INPUT or OUTPUT chains.
The "nat" table contains chains for packets that get altered by rules. Built-in chains for "nat":
PREROUTING - Alters packets before routing to INPUT or FORWARD.
OUTPUT - Alters packets after INPUT and before OUTPUT.
POSTROUTING - Alters packets after OUTPUT or FORWARD.
PREROUTING is used to alter the packet destination (DNAT). This is used, for example, when you want to route mail or web traffic to some other machine on your LAN.
POSTROUTING is used to alter the packet source (SNAT). This is used to allow machines on your LAN to share a single IP address on the internet.
To really see what's going on, you need to study this diagram.
-t TableName (default is filter)
-A ChainName to append this new rule
-s Source IP address
-d Destination IP address
-i Input interface
-o Output interface
-p IP protocol
-j Target
--sport Source port
--dport Desination port
Examples:
To drop all packets from an ip address stored in "badGuy":
iptables -t filter -A INPUT -i eth0 -s $badGuy -j DROP
To pass all mail arriving on "netDev" to "anotherIP":
iptables -t nat -A PREROUTING -i $netDev -p tcp \
--dport smtp -j DNAT --to-destination $anotherIP:smtp
In the example above, the packet destination will be altered so it goes to $anotherIP. The FORWARD chain will then process the packet becase the source and destination are now external. If the the default policy for the FORWARD chain is not ACCEPT, you need to add this rule:
iptables -t filter -A FORWARD -i $netDev -p tcp \
--dport smtp -d $otherMachine -j ACCEPT
The flags are used to match various parts of the IP and/or TCP header.
To really see what's going on, you
need to study this [diagram.](TCPIPHeaders.txt)
tcp, udp, icmp
http, ftp, nntp, pop3, imap, smtp, ssh, domain
iptables -F optionalChainName
iptables -X optionalChainName
iptables -Z optionalChainName
iptables -N newChainName
Only valid for built-in chains (INPUT, OUTPUT, etc.) The policy target cannot be another chain.
iptables -P chainName target
iptables -L optionalChainName
iptables -L optionalChainName -n -v
iptables -t filter -F
iptables -t filter -X
iptables -t filter -Z
iptables -t nat -F
iptables -t nat -X
iptables -t nat -Z
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT
-j LOG --log-prefix "Firewall: My rule fired"
The static IP of the server is in the variable $inetIP
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o $inetDev -j SNAT --to-source $inetIP
iptables -A FORWARD -i $lanDev -j ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward
echo 1 > /proc/sys/net/ipv4/ip_dynaddr
iptables -t nat -A POSTROUTING -o $inetDev -j MASQUERADE
iptables -t nat -A PREROUTING -i $inetDev -p $proto --dport $port
-j DNAT --to-destination $targetIP:$port
iptables -A FORWARD -i $netDev -p $proto --dport $port
-d $targetIP -j ACCEPT
Where: $inetDev = Device for incomming packets $proto = Protocol: tcp, udp, or icmp $port = The port you want to forward $targetIP = The target server
When the system boots, the firewall configuation is restored from:
/etc/sysconfig/iptables
This file can be updated by using the command
iptables-save > /etc/sysconfig/iptables
Enable the script at boot time using
chkconfig --add iptables
Other init script operations:
service iptables start # Apply /etc/sysconfig/iptables
service iptables stop # Admit all packets (remove firewall)
service iptables panic # Stop all incoming packets
service iptables restart # Reload the tables
service iptables save # Does iptables-save for you
service iptables status # Display the tables
IMPORTANT: Changing the value of ip_forward resets many other parameters to their default values. Your script should always set the value of ip_forward first!
Bash commands to configure the kernel:
echo 1 > /proc/sys/net/ipv4/ip_forward
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
echo 1 > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter
echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
Alternatively, the /proc settings may be configured in the file /etc/sysctl.conf:
net.ipv4.ip_forward = 1
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.tcp_syncookies = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.all.accept_redirects = 0
At boot time, sysctl.conf is loaded by /etc/rc.d/rc.sysinit
dmesg
Add 'confirm' (no quotes) to the lilo command line:
Example, At the lilo promp:
LILO: vmLinuz confirm
uname -a
uname -r
rdev /dev/fd0 /dev/hda7
rdev anImageFile
rdev anImageFile /dev/hda7
mknod /dev/name type major minor
Where type is p b c or u
pcinitrd --all myInitrdFile
mount -t ext2 -o loop myInitrdFile /mnt/initrd
You have to gunzip compressed images first.
ulimit -c <size>
You can disable core dumps by putting "ulimit -c 0" in:
/etc/profile
cardctl { suspend, resume, status, eject, insert } slot#
cardinfo # X interface for cardctl
dd if=/boot/vmlinuz of=/dev/fd0 bs=8192
loadlin vmlinuz initrd=myGZippedFileSystemImage
echo anInteger > /proc/sys/kernel/file_max
depmod -a
lilo
sync
logger -t MyProgram "This is a message"
Also see "man initlog" for debugging init.d scripts.
Update /usr/src/linux symbolic link to point at sources. Go into /usr/src/linux Backup .config to a safe place if you want to keep a copy.
make mrproper (Will delete old .config)
make xconfig (Fill in the blanks and write the .config file)
OR Copy in an old .config file and do:
make oldconfig
Edit the Makefile to bump the version number!
make dep clean bzImage install ;
make modules modules_install
If your root device has a modular driver you will need an initial ram disk at boot time. For kernel/module version set xx.yy.zz use:
mkinitrd /boot/initrd-xx.yy.zz xx.yy.zz
This will build a ramdisk file system image that contains all the loadable modules for block devices described in your /etc/conf.modules file. See also pcinitrd for PCMCIA boot devices.
Add another entry for your old kernel to lilo.conf & run lilo. Move any modules you don't build (like dpc) Some versions of gcc are not compatible with some kernels. Redhat supplies a "kgcc" for these systems.
OBSOLETE: This is part of the kernel make process now! Preserve the Redhat-modified /etc/pcmcia/network script. In the pcmcia-cs source directory:
make clean config
Answer the questions: Symbols from the source tree and don't say yes to the plug & play bios question.
make all install
Restore the redhat version of /etc/pcmcia/network
Put the patch file in /usr/src (above 'linux') and cd there.
Then:
patch -s -p0 < patchfile
Add the --dry-run option
cp zImage /dev/fd0
Build cross versions of binutils and gcc:
Example:
ARCH := ppc
CROSS_COMPILE =powerpc-linux-
The need for this arrises when you forget to lilo a new kernel.
Boot from a CD or floppy, mount the target Linux partition. Then:
chroot linuxPartition lilo
Used when telneting to unusual systems
stty erase <press a key>
showkey
xset r
xmodmap -e "keycode 22 = BackSpace"
xmodmap -e "keycode 107 = Delete"
Physical Volume - A whole disk or a partition on a disk.
Volume Group - A collection of physical volumes.
Logical volume - A "partition" on a Volume Group.
If LVM has never been used on a system, first run vgscan to create the /dev directory and other structures.
Each partition must have a partition type of 0x8E. (Use fdisk)
(This does not apply if you are using a whole disk.)
For the commands that follow, the size may have a suffix:
None filesystem blocks
s 512 byte sectors
K Kilobytes
M Megabytes
G Gigabytes
pvcreate /dev/hdb # A whole disk
pvcreate /dev/hda3 # A partition
An error may be reported if you try to create a physical volume from a whole disk that had partitions defined. To destroy the partition table for a whole disk:
dd if=/dev/zero of=/dev/hdb bs=1K count=1
blockdev --rereadpt /dev/hdb
vgcreate myVG /dev/hdb /dev/hda3
Note: If you are using devfs, you must use the whole physical name not just the symbolic link in /dev. For example:
/dev/ide/host0/bus0/target0/lun0/part1
vgextend /dev/myVG /dev/hda5
This can be done live, but first you have to make sure all the extents in use on the physical volume are moved to other physical volumes in the group. For example, to move everything off partition hda3:
pvmove /dev/hda3
Now it is safe to remove the physical volume:
vgreduce /dev/myVG /dev/hda3
Make sure everything is unmounted, then:
vgremove myVG
lvcreate --size 200M --name myVol myVG
You can now use this logical volume like a normal partition
mkfs -t ext2 /dev/myVG/myVol
mount -t ext2 /dev/myVG/myVol /mnt/myMP
lvreduce -r --size newSize /dev/myVB/myVol
lvextend -r --size newSize /dev/myVB/myVol
lvreduce -r --size -someSize /dev/myVB/mySource
lvextend -r --size +someSize /dev/myVB/myDest
vgchange -a y myVG
vgchange -a n myVG
vgscan
vgchange -a y
umount /mnt/myMP
lvchange --available n /dev/myVG/myVol
lvremove /dev/myVG/myVol
Make sure all the logical volumes are unmounted!
vgchange --available n /dev/myVG
vgremove /dev/myVG
A snapshot lets you do a backup of the instantanious state of a logical volume. You create a snapshot, back it up, and then delete the snapshot. Conceptually, the snapshot is a copy of the whole drive frozen in time.
How to do an rsync backup of "myVol" using a snapshot:
lvcreate --size 200M --snapshot --name snapVol /dev/myVG/myVol
mount -t ext2 /dev/myVG/snapVol /mnt/snap
rsync -a --delete /mnt/snap/ /mnt/backups/myVol
umount /mnt/snap
lvremove /dev/myVG/snapVol
The neat thing about this is that the size of snapVol can be much smaller than the size of myVol - The snapVol really contains only the changes being made to myVol while the snapVol exists. When you remove the snapVol, the changes somehow get "put back" on myVol. (I'm not sure if this is exactly how it works, but this is how it appears to work.)
pvscan # Display all physcial volumes
lvscan # Display all logical volumes
pvdisplay /dev/hda4 # Display the state of a physical volume
vgdisplay /dev/myVG # Display the state of a volume group
lvdisplay /dev/vg1/archVol # Display the state of a logical volume
Leave out the parameter and the xxdisplay commands will show everything.
vgscan
pvcreate /dev/hdb
vgcreate vg1 /dev/hdb
lvcreate --size 30G --name backVol vg1
lvcreate --size 40G --name archVol vg1
lvcreate --size 4G --name tempVol vg1
mkfs -t ext2 -j /dev/vg1/backVol
mkfs -t ext2 -j /dev/vg1/archVol
mkfs -t ext2 /dev/vg1/tempVol
pvcreate /dev/hda4
vgcreate vg2 /dev/hda4
lvcreate --size 5G --name homeVol vg2
lvcreate --size 9G --name wwwVol vg2
lvcreate --size 1G --name spoolVol vg2
lvcreate --size 3G --name tempVol vg2
mkfs -t ext2 -j /dev/vg2/homeVol
mkfs -t ext2 -j /dev/vg2/wwwVol
mkfs -t ext2 -j /dev/vg2/spoolVol
mkfs -t ext2 /dev/vg2/tempVol
tail -f /var/log/messages # Tail the log to stdout
vi /var/log/messages # Inspect the log with an editor
logger This line is appended to the log.
logger -t MYTAG This line gets a MYTAG: prefix
Display the entire journal for all available boots
journalctl
Display the journal without the pager
journcalctl --no-pager
Capture the most recent boot in a text file
journcalctl -b --no-pager > /root/journal.txt
Tail the active log
journalctl -f
Display the journcal since the most recent boot
journalctl -b
List all available boots
journalctl --list-boots
Display the journal for the nTh boot
journalctl -b n
(n=1 is the oldest)
Display the journal for the previous nTh boot
journalctl -b -n
(n=-1 is previous)
Show messages that have a specified tag
journalctl -t tagName
Show messages only from a specified systemd service
journalctl -u serviceName
Common tag names
kernel
sendmail
dovecot
spamd
named
sshd
smartd
zed
There are many other options, but it's often easier to grep the output when looking for details. Example:
journcalctl -b --no-pager | grep <whatever>
Write to syslog from shell
echo "This is message 1" | system-cat
echo "This is message 2" | system-cat -t mything
From the previous example, journald -f will show:
Feb 05 07:14:44 server unknown[2655]: This is message 1
Feb 05 07:14:55 server mything[1335]: This is message 2
Install the server and client rpms.
rpm -i mysql-server...
rpm -i mysql-...
Configure for autostart at boot time
chkconfig --del mysqld # To clean up
chkconfig --add mysqld # Add to the runlevels
Start the service immediately
service mysqld start
Set the root password for the first time
mysqladmin password firstPassword
Using mysqladmin:
mysqladmin --password=oldPassword password newPassword
The mysqladmin statements show here assume you are logged in as root. Otherwise add the parameter: --user=root
Alternative method using the mysql client:
update mysql.user set password=password('newpassword') where user='root';
flush privileges;
Key concept: mysql usernames and passwords have nothing to do with Linux usernames and passwords: You must explicitly authorize all mysql users. (See the GRANT command below.)
mysql --user=myName --password=xxxyyy
If you don't specify the database user name,
mysql will try to connect using your linux user name.
If you don't specify a username or password on the mysql command line, the values (if present) will be take from the configuration file.
Edit: /etc/my.cnf
Add (or edit) this section:
[client]
user=myName
password=myPassword
show databases ;
If you are not logged in as the mysql administrator, you will only see the databases you have privileges to access.
It is the usual practice that only the mysql administrator creates new databases. From within mysql, this command line adds a new database:
create database databaseName ;
A new database can also be created from the shell:
mysqladmin --password=password create databaseName
From inside mysql:
drop database databaseName ;
From the shell:
mysqladmin --password=password drop databaseName
1) You can't drop a database that some program is using.
2) On some versions of MySQL, deleting a database is more involved. When you try to drop a database, the "show databases" command will show that the database is still there. This occurs because some files are left in the top-level database directory. On Redhat/Fedora installations, the top-level database directories are located in /var/lib/mysql. After the first "drop database" fails, delete all the debris in the top-level database directory. A second "drop database" command will now succeed.
Access privileges are assigned to a username/hostname combination. The syntax looks like an email address: "username@hostname".
Adding a user simply means allowing a username@hostname to perform certain operations on all or part of one or more databases.
The most typical case is to assign all privileges to some user who manages the database. If this username and hostname are new, this operation "adds" the new user:
grant all privileges
on databaseName.*
to username@localhost
identified by 'aPassword' ;
The wild card * in the example above refers to all table names. (Even though the database may not have any tables yet.)
The "grant" command may be used multiple times to allow access from other hosts or to assign different privileges to different tables for the same user.
If a user must be able to grant access to other users, the grant command must be used again with a special option:
grant grant option on databaseName.* to username@localhost ;
A user can only grant privileges to others that they already have on the database.
Removing a user means removing the privileges of the username@hostname from all or part of a database:
revoke all privileges on *.* from username@localhost
If you are sure that a username@hostname has been revoked on all databases, you can purge the user from the mysql database:
delete from mysql.user where user='username' and host='hostname' ;
flush privileges ;
select host,user from mysql.db where db="databaseName" ;
select host,user,db from mysql.db ;
select host,user,password from mysql.user ;
set password for user@somehost.somewhere=password('newpassword') ;
mysql --password=xxxyyy dataBaseName < configFile.sql
use dataBaseName ;
show tables ;
describe tableName ;
show columns from tableName ;
create table pet
( name VARCHAR(20),
owner VARCHAR(20),
species VARCHAR(20)
) ;
char(size)
Fixed-length character string.
Size is specified in parenthesis.
Unused positions are padded with spaces.
varchar(size)
Variable-length character string.
Max size is specified in parenthesis.
Limit is 255 bytes. (1 byte size field)
text
A large block of variable-sized text.
Limit is 65535 bytes. (2 byte size field)
int
4 byte signed integer value.
float
4 byte floating point value
date
Date value
time
Time value
Each column is defined by a name, data type and optional constraint.
Example constraints:
unique
not null
primary key
default <default_value>
Note the use of NUL and quotes around string values.
insert into pet values
( 'Puffball',
'Diane',
'hamster'
) ;
load data local infile "pet.txt" into table pet ;
Note the use of \N for null values.
Fido Mary \N
insert into pet (name, owner) values ('Goober', 'George') ;
insert into pet select (name, owner) from oldpet ;
insert into pet(owner, species) select owner, species from table where name="Puffball" ;
Note that we must leave out the 'name' column or we'll have a duplicate. To fix the name (which will be null) use:
update pet set name="Marvin" where name is null ;
delete from pet where name = 'Puffball' ;
delete from pet
drop table tableName
update tableName set columnName1=value1, columnName2=value2,...
where optionalConditions ;
update pet set species="alien" where name="Leo" ;
update table1, table2,...,tableN
set table1.column1=table2.column2,...
where optionalConditions ;
update new,old set new.email=old.value
where new.name=old.name and old.type="Email";
alter table tableName add newColumnName dataType
alter table tableName add newColumnName dataType first
alter table tableName add newColumnName dataType after otherColumnName
alter table tableName drop columnName
alter table tableName modify columnName newDataType
alter table tableName modify columnName dataType first
alter table tableName modify columnName dataType after otherColumnName
alter table tableName change oldColumnName newColumnName dataType
alter table oldTableName rename newTableName
alter table tableName alter columnName set default someValue
alter table tableName modify column columnName dataType after otherColumnName
alter table tableName modify column columnName dataType before otherColumnName
alter table tableName modify column columnName dataType first
This is not-destructive, but you must supply the correct dataType for the column.
select <what to select> from <which table> where <conditions>
<what to select> a list of columns or * for all columns
select * from pet
set autocommit=1; # Used for quick re-create of the table
delete from pet;
load data local infile "pet.txt" into table pet ;
select * from pet where name = "Bowser" ;
select * from pet where species = "dog" and owner = "smith" ;
select name, birth from pet;
select owner from pet ;
select name, owner from pet where species in ('dog', 'cat') ;
select distinct owner from pet ;
select name, birth from pet order by owner ;
select name, birth from pet order by birth desc ;
select name, species, birth from pet order by species, birth desc ;
select pet.name, pet.age, employee.salary, employee.title
from pet, employee where pet.name = "Bugsy";
The configuration file must be changed so the daemon mysqld will listen on a tcp interface rather than just the local socket.
/etc/my.cnf:
...
bind-address=myserver.mydomain.com
...
In the example shown above, the dns name must resolve to an ip address other than 127.0.0.1.
You'll need to restart the service:
service mysqld restart
Next the individual database users must be granted network access:
grant all privileges
on databaseName.*
to username@lclient.somedomain.com
identified by 'aPassword' ;
In this expression, client.somedomain.com is the machine where the database connection and queries will originate.
From the remote system (with mysql client installed) execute:
mysql -u remoteUser -h remoteHostIP -p
The -p will make it prompt for the remoteUser's password.
mysqldump --user=userName --password=aPassword \
dbName > backupFile.sql
mysqldump --user=userName --password=aPassword --xml \
dbName > backupFile.xml
Create an empty database with the same name and privileges.
Next: use yourDatabase ; source backupFile.sql ;
Or from the shell:
mysql --user=userName --password=aPassword --host=hostName \
dbName < backupFile.sql
Create a text file with two lines:
UPDATE mysql.user SET Password=PASSWORD('myNewPassword') WHERE User='root';
FLUSH PRIVILEGES;
Save this as:
mysql-reset.sql
Stop the sql server.
Restart the server from the command line using this form:
mysqld --init-file=mysql-reset.sql
The name of the server will vary. Examples:
Windows: mysqld.exe
Linux: mysqld_safe
Now restart the server in the usual way.
After performing a grant to someuser@localhost, you may find that an external application configured to access the database will not be able to connect.
Many Linux configurations will have an /etc/hosts file that contains:
127.0.0.1 myname.mydomain myalias localhost.localdomain localhost
When DNS (named) is not configured and running, the /etc/hosts file is used for forward and reverse lookups. It appears that many programs do some sort of security checking before connecting to MySQL by looking up "localhost" and then doing a reverse lookup on the result. The reverse lookup on "127.0.0.1" using the /etc/hosts file shown above will yield: "myname.mydomain.com". This string gets used when connecting to MySQL, which fails because it doesn't match the string "localhost" in the SQL grant expression.
To fix this (only for machines without DNS), I suggest that
/etc/hosts contain:
127.0.0.1 localhost localhost.localdomain myname myname.mydomain
In other words, make sure localhost is the first name. A better solution is to run DNS... (See the DNS section)
After attempting to drop a database, you see an error of the form:
MySQL "Error dropping database (can't rmdir" "errno: 41"
First, locate the data directory for your database using the command:
select @@datadir ;
Go to that location. Enter the directory for your problem database. Delete the files indide (not the parent directory!) Back at the MySQL command line, drop the database.
Install the server and client rpms
yum install postgresql
yum install postgresql-server
Initialize the database
service postgresql initdb
Configure for autostart at boot time
chkconfig postgresql on
Start the service
service postgresql start
psql
\h Help with SQL
\? Help with psql
\q Quit
\l SHOW DATABASES
\d SHOW TABLES
\d table SHOW COLUMNS
SELECT yourDatabase FROM pg_database ;
SELECT table_name FROM information_schema.tables
WHERE table_schema='public';
SELECT column_name FROM information_schema.columns
WHERE table_name='yourTable'
ORDER BY ordinal_position ;
The ORDER BY clause is optional and will display the columns in the order they were defined.
/var/lib/pgsql/data/pg_log
http://www.postgresql.org/docs/8.0/static/index.html
ifup <interface>
ifdown <interface>
These commands are scripts that automatically set up all the ip parameters and take care of special cases such as PPP, PPPoE, DHCP, firewalls and others.
In Redhat-like systems, extra implicit parameters go in:
/etc/sysconfig/network
/etc/sysconfig/network-scripts/ifcfg-<interface>
ifconfig # Show params for active interfaces
ifconfig -a # Show params including inactive interfaces
ifconfig <interface> # Show params for a specific interface
ifconfig <interface> \ # Set params and start the interface
address <ipaddress> \
netmask <mask> \
broadcast <address> \
metric <ametric>
The ifconfig command directly configures and starts the interface. It is up to you to take care of routing and other issues.
route -n # List numbers, not names
route add default <dev> # Add a default route
route delete <dev> # Remove a route
exportfs -r
Display available interfaces:
tcpdump -D
Show all traffic from all interfaces
tcpdump -i all
Show all traffic on a specific interface:
tcpdump -i eth0
Show input and output associated with a specific host:
tcpdump host <host>
Only input from the host:
tcpdump src <host>
Only output to the host
tcpdump dst <host>
When using src or dst, you may also specify a port:
tcpdump src <hostIP> port 80
The first parameter to tcpdump can be the name of a protocol:
tcpdump <protocol> host <hostIP>
<protocol> may be: tcp, udp, arp, icmp
Network addresses
tcpdump -i eth0 dst net 192.168.1.0/24
Special addresses
tcpdump -i eth0 broadcast
tcpdump -i eth0 multicast
If you run this from a remote session, you will want to ignore your own terminal traffic:
tcpdump -i eth0 host not <myAddress>
Or: (to ignore ssh traffic)
tcpdump -i eth0 port not 22
Don't resolve ip names:
tcpdump -n ...
Port ranges:
tcpdump dst host <hostIP> dst portrange 1-80
Logical expressions:
tcpdump "icmp or udp"
tcpdump "dst host <hostIP> and (dst port 80 or dst port 443)"
tcpdump "broadcast or multicast"
Capture a specific number of bytes from each packet (default is 68)
tcpdump -s 23 ...
Capture all of the packet (instead of 68 bytes)
tcpdump -s 0 ...
You can send output to a file:
tcpdump ... -w aFile.txt
You can play the file back into tcpdump:
tcpdump -r aFile.txt
Less verbosity:
tcpdump -q ...
More verbosity:
tcpdump -v
tcpdump -vv
tcpdump -vvv
The interface will expose more information if it operates in promiscuous mode:
ipconfig eth0 promisc
You will want to turn this off after debugging:
ipconfig eth0 -promisc
hostnamectl
hostnamectl set-hostname goober.csparks.com
Add the path as a parameter to the tftp daemon in inetd.conf
ssh user@remoteMachine anyCommand
Any text output from the command will be displayed locally. You must have appropriate keys configured. See the SSH section for details.
host hostName
dig hostName
nslookup hostName <dnsServerName>
ping hostName
ping ipAddress
netstat -vat
netstat -n --inet
netstat -ntp
netstat -tupl
nmap -sT hostName
Example - List sshd ports:
ss -anp | grep LISTEN | grep sshd
Bind the port with a process:
nc -l myPort &
Check to see if it worked:
netstat -nlp | grep myPort
Kill the process when finished:
killall nec
dhclient -nw
iwconfig # Show params for active interfaces
iwconfig eth0 essid GOOB # Set the network name to GOOB
iwconfig eth0 key 43224598a34bc2d457e2 # Specify a hex WEP key
iwconfig eth0 key s:ThisIsAnAsciiPassphrase
Show all settings:
ethtool eth0
Show the speed:
ethtool eth0 | grep Speed
Show duplex setting:
ethtool eth0 | grep Duplex
Modify duplex setting:
ethtool -s eth0 duplex half
ethtool -s eth0 duplex full
Change several settings at once:
ethtool -s eth0 speed 100 autoneg off
nmcli general status
nmcli connection show
nmcli connection show --active
nmcli connection up <A CONNECTION>
nmcli connection down <A CONNECTION>
nmcli radio wifi
nmcli radio wifi on
nmcli radio wifi off
nmcli device wifi list
nmcli device wifi rescan
nmcli device wifi connect <SSID NAME> password <YOUR PASSWORD>
nmcli device status
nmcli device disconnect <A DEVICE>
nmcli device connect <A DEVICE>
nmcli device disconnect <dev>
nmcli connection add <A CONNECTION> \
ipv4.method static \
ipv4.addresses 192.168.1.100/24 \
ipv4.gateway 192.168.1.2 \
ipv4.dns 8.8.8.8
nmcli connection modify <A CONNECTION> \
ipv4.method auto
nmcli connection modify <A CONNECTION> connection.autoconnect yes
nmcli connection modify <A CONNECTION> connection.autoconnect no
nmcli connection modify <A CONNECTION> con-name <A NEW NAME>
"con-name" is equivalent to "connection.id"
nmcli connection add type ethernet \
ifname <A DEVICE> \
con-name <A CONNECTION \
...
nmcli --ask connection add
nmcli con add type vpn ifname murgurk \
vpn-type org.freedesktop.NetworkManager.l2tp \
vpn.secrets "password=myPassword" \
vpn.data "\
gateway=server.csparks.com, \
ipsec-enabled=yes, \
user=hugh, \
mru=1400, \
mtu=1400, \
ipsec-psk=myBigPSK"
This example creates an L2TP/IPSEC vpn, but many other types are supported.
- A NetworkManager plugin is required for each type.
- The vpn.data will have different key=value sets for each vpn-type.
Example: For PPTP, install the plugin:
NetworkManager-pptp
And the vpn-type will be:
org.freedesktop.NetworkManager.pptp
The fashonable trend in linux is giving ethernet devices ever-more bizarre and unmemorable names. There are no doubt very good reasons. To rename a device:
nmcli con mod <A CONNECTION> connection.interface-name <A NEW DEVICE NAME>
This is a rare problem, but it's possible for nmcli to "loose" the MAC address associated with a device. Make sure nmcli knows the MAC address before attempting to rename a device:
nmcli con show <A CONNECTION> | grep 802-3-ethernet.mac-address
If you don't see a MAC address, get it using lower-level tools:
ip link show <CURRENT DEVICE NAME>
Associate the MAC address with the nmcli device:
nmcli con mod <A CONNECTION> 802-3-ethernet.mac-address "xx:yy:zz..."
Now you can proceed with renaming the device. (And reboot.)
openssl genrsa -des3 -out server.key 1024
openssl rsa -in server.key -out server.key.open
This is the key file required by apache and sendmail.
This is essentially your certificate in the unsigned form.
openssl req -new -key server.key -config openssl.conf -out server.csr
You get pestered for a description of your business. The important thing is the "Common Name": That is the domain name you want certified.
Common name example: myhost.mydomain.com
This step uses your key to sign the certificate: (An alternative is to pay to have an agency sign it. See below.)
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt
You can install this in apache, sendmail and other applications. The clients will complain that the certificate cannot be verified because there is no chain of trust. Most applications will let you add the certificate to the local database anyway. Then you won't be troubled.
openssl x509 -in server.crt -noout -text
This is an alternative way to sign your server.csr. It introduces the concept of a certificate authority.
A "real" purchased certificate will be signed by an authority already known to the client operating system such as Thwait, Verisign, or GoDaddy.
Creating your own certificate authority won't save you from having the client applications nag the user about an untrusted certificate. But the client can choose to install the new certificate authority as "trusted." This has the small advantage that all other certificates you sign with the same CA will be accepted by that client without complaints.
openssl genrsa -des3 -out server-ca.key 4096
The common name you use CANNOT be the same as the name used in the certificates you want to sign.
Example: authority.csparks.com
openssl req -new -x509 -days 365 -key server-ca.key -out server-ca.crt
openssl x509 -req -days 365 -in server.csr -CA server-ca.crt -CAkey server-ca.key -set_serial 01 -out server.crt
This replaces your old self-signed server.crt
Proceed as above to create a certificate signing request. Then pay an agency to sign it and send it back. I've used GoDaddy, which is easy and inexpensive. You get back two files:
your.domain.com.crt
gd_bundle.crt
The first is your certificate, signed with your private key and signed again by godaddy's private key. Someone who wants to deal with you can decrypt the certificate using godaddy's public key followed by your public key. The proves that you signed it and that godaddy (hopefully) took pains to verify your identity.
The gd_bundle.crt file contains the certificate authority path for godaddy.
openssl verify -CAfile gd_bundle.crt your.domain.com.crt
Run the openssl server:
openssl s_server -cert server.crt -key server.key -www
If the server starts quietly, all is probably well. Visit the server on your local LAN with the URL:
https://yourserver:4433
In the url, "yourserver" should be the name the cert certifies. You should see a page full of information about openssl and your certificate.
Run the server side program. (whatever...) On the client side:
openssl s_client -connect your.server.com:your_port -crlf
Now you can type plain text commands and see the responses.
sgdisk -p /dev/sda
sgdisk --list-types
sgdisk -n 1:0:200Mib -t 1:EF00 -c 1:EFI /dev/sda
-n a:b:c
a: Partition number
b: Start location (0 => next available)
c: End location (0 => end of disk)
-t a:c
a: Partition number
c: Partition type code
-c a:n
a: Partition number
n: Name of the partition (label)
sgdisk -d 1 /dev/sda
sgdisk -Z /dev/sda
sfdisk -d /dev/sda > myLayout.dat
sfdisk -f /dev/sda < myLayout.dat
sfdisk -d /dev/sda | sfdisk -f /dev/sdb
oldFile # Path to the unmodified file
newFile # Path to the modified file
diff -u oldFile newFile > patchFile
-u Use uniified output format
oldPath # Path to the unmodified files
newPath # Path to the modified files
diff -urN oldPath newPath > patchFile
-u Use unified format
-r Perform diff recursively
-N Support creating new files
For -p0, you want to be in the same place you made the diff.
patch -u -s -pN < patchFile
OR
patch -u -s -pN -i path/patchFile
-u Use unified format
-s Silent
-pN Remove first N components of file path names
-d x Switch to the directory named by x
For individual file patches, -p0 is used if you're in the same directory as the unpatched file.
For directory patches, -p1 is used to apply the patch from inside the as-yet unpatched directory.
Perl has it's own "module" (package) manager called CPAN. It is only necessary to use CPAN if there is no perl-XXXX rpm available, so first try using
yum list perl-XXXX
To install CPAN:
yum install perl-CPAN
I found that perl wanted this as well:
yum install perl-YAML
One-line command:
perl -MCPAN -e 'install XXXX::YYYY'
If you have several modules to install or want confirmations you can enter the CPAN shell:
perl -MCPAN -e shell
Ask for confirmations:
o conf prerequisites_policy ask
Install the module(s)
install XXXX::YYYY
install PPPP::QQQQ
...
perldoc perllocal
You need to do this if you have downloaded and upacked a package by hand. Navigate into the directory and execute:
perl Makefile.PL;
make
make test
su
make install
lpr myfile
lpr -P printer myfile
lpr myfile -o page-left=60
Units are points = 1/72"
lpstat -p
lpstat -d
lpoptions -d LaserJet
lpadmin -d LaserJet
lpq
lprm nn
lprm -
lpc
http://localhost:631
Determine the remote printer name:
smbclient -L hostname -U%
If a username and password are required by the host, use:
smbclient -L hostname -U username%password
(In this case, the printer was called "Deskjet")
1) Device: Windows Printer via Samba 2) URI: smb://username:password@sparksvaio/Deskjet 3) Driver: HP New Deskjet Series Cups v1.1 (en)
1) Device: Parallel Port #1 (Hewlett-Packard HP LaserJet 4000 Series)
2) Driver: HP LaserJet Series CUPS v1.1 (en)
/usr/share/cups/model
hp4000.ppd.gz
hp970Cse.ppd
These came from the sourceforge project sponsored by HP. The hp970Cse.pdd requires foomatic which requires a TON of perl stuff. If you don't want all this, the cups built-in "New Deskjet" works fine.
This is caused by a bug that has been in Samba for many years. It is evidently nearly impossible to fix in the Samba code. Fortunately, there is an easy work-around to clear up the problem. Stop the samba service and delete all the .tbd files in the printer cache: service smb stop rm -rf /var/cache/samba/printer/*.tbd service smb start
1) Select LPD/LPR Protocol. 2) Device URIs for each port:
lpd://Sc0405b5/L1
lpd://Sc0405b5/L2
3) Select the drivers
HP New Deskjet Series Cups v1.1 (en)
HP LaserJet 4000 Series PS (en)
Newer versions of Windows refuse to connect to some-but-not-all Linux/CUPS printers. The error message includes the code: 0x000006d1. The fix is not obvious: Using the Add Printer dialog:
Add a local printer.
Select "Create a new port".
Select "Local port".
For the port name, enter the Samba path, e.g.:
\\server\hp3600
Select the right driver in the usual way.
ps ax
killall name
kill pid
kill -s 9 pid
command &
First break with control Z, then
bg
jobs
fg
kill
stop
Just type:
nohup command > /dev/null 2>&1 &
cc file1.c file2.c file3.c -o program
cc -c file.c -o file.o
ld file1.o file2.o file3.o -o result
ldd <program>
nm <objfile>
ldconfig
An ".so" library can be used with dlopen, dlclose, dlsym to link with a library while a program is running.
Example library mylib.c:
int myFunction(int a, int b)
{ return a + b ;
}
Create the dynamic library:
cc -rdynamic -c myLib.c -o myLib.o
ld -shared myLib.o -o myLib.so
Client program demo.c:
#include <dlfcn.h>
#include <stdio.h>
int main()
{ int p1 = 1 ;
int p2 = 2 ;
void *mylib = dlopen("./myLib.so", RTLD_LAZY) ;
int (*myFunc)() = (int(*)())dlsym(myLib, "myFunction") ;
int result = (*myFunc)(p1, p2) ;
printf("Result: %d\n", result) ;
}
Compile and run the demo:
cc -ldl demo.c
./demo
linear: Combines several disks into one big disk: "JBOD" (Just a Big Old Disk) raid0: Striping - Blocks for a file are spread out on all the disks. Used to get speed. No safety. raid1: Mirroring - Two (or more) drives operate in parallel with duplicate data. Used to get safety. No extra speed. raid4: Block-level striping with a dedicated parity disk. Uses less space than mirroring. Can recover from one drive failure. raid5: Block-level striping with distributed parity. Like raid4, but parity information is distributed between all drives. Can recover from one drive failure. Faster than raid4. raid6: Block-level striping with double distributed parity. Can recover from 2 failed drives. raid10: A stripe (RAID0) of mirrors (RAID1) Used to balance safety and speed. raid01: A mirror (RAID1) of stripes (RAID0). Used to balance safety and speed.
In this example, we create a RAID 1 group using two drives. Each drive needs to have a partition of the same size and type.
The first step is to use fdisk to create the partitions and set their partition types. For reasons beyond the scope of this tutorial, it's best to use partition type 0xDA "Non-FS data", rather than the old standard, 0xFD "Linux RAID autodetect".
For this example we will assemble two partitions:
/dev/sda1
/dev/sdb1
You can verify the partition types using:
fdisk -l /dev/sda
fdisk -l /dev/sdb
If you need to change the partition types, run fdisk without the "-l" and you'll get a menu with obvious options.
mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/sda1 /dev/sdb1
This command creates a mirror md0 by combining the two partitions.
mkfs -t ext4 /dev/md0
The /dev/md0 device behaves like any other drive.
e2label /dev/md0 mrbig
We will use this label when mounting the array in /etc/fstab, rather than the device name for reasons explained below.
To mount from the command line:
mount -t ext3 /dev/md0 /mnt/myarray
Or you could use the label:
mount -t ext3 -L mrbig /mnt/myarray
To mount in /etc/fstab:
LABEL=mrbig /mnt/myarray ext4 defaults 0 2
It's better to use a LABEL because the raid array may not be assembled when the startup scripts first attempt to process fstab. Most linux distributions have startup scripts that will defer mounting labeled devices because the label obviously can't be read until the device is operational.
cat /proc/mdstat
mdadm --detail /dev/md0
mdadm --examine /dev/some_part
On most Linux systems, one of the startup scripts will run the command:
mdadm --assemble --scan
Or more concisely:
mdadm -As
The mdadm program will search for disk drives and parititions that are parts of raid arrays and assemble them automatically. They are recognized by a special raid superblock which is independent of the regular file system-dependant superblock.
The mdadm program will also look at a configuration file when assembling arrays:
/etc/mdadm.conf
It is possible to specify everything in this file, rather than relying on automatic assembly. To create this file, first assemble the RAID array by hand as shown above. Then run the command:
mdadm --examine --scan > /etc/mdadm.conf
Here's an example mdadm.conf created with this command:
ARRAY /dev/md0 UUID=915ee2a0:945b381d:30f19119:18fab9e7
The UUID is unique for this array. It functions at the device level much like an e2fs label does at the filesystem level: It allows the array to be identified regardless of the device names assigned to the components.
You can see more details using:
mdadm --detail --scan --verbose
Example:
ARRAY /dev/md0 \
level=raid1 \
num-devices=2 \
metadata=1.2 \
UUID=915ee2a0:945b381d:30f19119:18fab9e7 \
devices=/dev/sda1,/dev/sdb1
It's not a good idea to use this format for your mdadm.conf because device names can change when drives are added or removed. It is, however, useful to keep a copy of this information somewhere to help with recovery if the raid array gets broken:
You can assemble a specific array using a command of the form:
mdadm --assemble --scan /dev/md0 --uuid=915ee2a0:945b381d:30f19119:18fab9e7
Obviously, you have to know the UUID.
Modern Linux distributions usually scan and assemble raid arrays in their normal startup scripts. It isn't necessary to use /etc/mdadm.conf at all unless you have some reason to override this mechanism or provide additional information. Everything linux needs is in the raid superblock written on each device or partition.
Add this line to /etc/mdadm.conf:
MAILADDR yourname@yourdomain.com
If anything goes wrong, you'll get a message. I use an /etc/mdadm.conf file with just this one line.
I like to use both. I put LVM on top of RAID: RAID provides physical safety and LVM provides the flexibilty of virtual partitions.
See the Logical Volumes section for details.
Start a scrub:
echo check > /sys/block/md0/md/sync_action
Check scrub progress:
cat /proc/mdstat
Stop a scrub early:
echo idle > /sys/block/md0/md/sync_action
Check the bad block count:
cat /sys/block/md0/md/mismatch_cnt
When you get a report about a mismatch count, for example on device md1:
Show the bad block count:
cat /sys/block/md1/md/mismatch_cnt
Start a repair:
echo repair >/sys/block/md1/md/sync_action
Check progress:
cat /proc/mdstat
You can watch continuously:
watch cat /proc/mdstat
When finished, start a scrub:
echo check > /sys/block/md0/md/sync_action
Check progress:
cat /proc/mdstat
When finshed, verify:
cat /sys/block/md1/md/mismatch_cnt
(Should be zero now...)
If a disk has problems, first mark it as "failed":
mdadm --manage /dev/md0 --fail /dev/sdb1
Then you can remove it from the array:
mdadm --manage /dev/md0 --remove /dev/sdb1
Just add the new disk:
mdadm --manage /dev/md0 --add /dev/sdb1
The disk will being synchronizing immediately.
Your supposed to be able to do this with everything online and mounted.
For this example, we'll assume the new drive name is /dev/sde1 and that we have a linear (JBOD) RAID array at /dev/md0.
Using fdisk, create one partition that fills the new drive. Make the partition type "fd", which is the code for "Linux RAID autodetect".
Check the status of the array to make sure it's happy:
cat /proc/mdstat
Check the filesystem on the array to make sure it's happy:
e2fsck -f /dev/md0
Add the new drive:
mdadm --grow --add /dev/md0 /dev/sde1
Expand the filesystem to fill the new space:
resize2fs /dev/md0
If you didn't do it live, remount md0.
Because linux can identify and assemble raid arrays without an mdadm.conf file, you can get into trouble if you add a random old disk drive to your system that happens to have a raid superblock. Especially if it was a replacement part of an array that has the same UUID. For this reason, it's a good idea to erase the raid superblocks when an array is no longer needed or if you want to redeploy the drives in some other configuration.
First unmount all filesystem on the array and remove them from /etc/fstab and/or /etc/auto.mount.
Next, stop the array:
mdadm --stop /dev/md0
Scan to display the drives or partitions used in the array:
mdadm --scan --details --verbose
Now you can remove the array:
mdadm --remove /dev/md0
To re-use the drives for some other purpose, you need to remove the raid id information. This is done by zeroing the raid superblocks on the drives. For example, if the scan shows these partitions as part of your raid array:
/dev/sdb2 /dev/sdc2 /dev/sdd2 /dev/sde2
Use this command:
mdadm --zero-superblock /dev/sd[bcde]2
Now all the drives are free to use however you like.
The dmraid format is/was used for an older method of doing software RAID. At boot time, most linux distributions will recognized dmraid superblocks (not the same as mdadm RAID) and try to build a raid array. To resuse these drives, you must first erase the dmraid information:
dmraid -E -r /dev/your_drive
Note that "your_drive" should be the name of the whole device, not a partition.
The dmraid utility supports multiple raid formats. In rare cases, you may need to specify which format you want to remove:
dmraid -E -r -f pdc /dev/your_drive
And/or:
dmraid -E -r -f nvidia /dev/your_drive
There are commands to stop, start, replace, grow, add, and delete drives. All while the raid array is running. To learn more:
man mdadm
Anchors
^ Beginning of the line
$ End of the line
< Left word boundary
> Right word boundary
Quantifiers
. Any single character except eol
x* Zero or more x's (maximal)
x+ One or more x's (maximal)
x? Zero or one x's (maximal)
x*? Zero or more (minimal)
x+? One or more (minimal)
x?? Zero or one (minimal)
Character classes
[abcdef] Any of the enclosed characters
[a-z] Any in the range of characters
[^a-e] Any char except a-e
[^abcdef] Not any of the characters
Expressions
(expression) Grouping an expression
\c Escape a meta character c like *+. etc.
exp1|exp2 Matches expression1 or expression 2.
The configuration examples shown in this section are for the 3Com OfficeConnect Remote 812 ADSL Router. It's one of the more capable consumer-grade products although now obsolete. Configuring other desktop routers involves very similar concepts.
Most routers are configured using a built-in webserver. After adding the static IP of the router to your DNS, you can visit it from any client on your LAN. Example:
http://router.csparks.com:8080
UNCHECK: Enable Bridging
CHECK: Enable IP Routing
UNCHECK: Enable IPX
IP Address & DHCP:
IP: 192.168.0.254
Mask: 255.255.255.0
Rip: None
Use this network as DHCP: No
DNS: Disable
IP Static Routes: None
IPX: All off
No filters
This is the main setup for the ADSL connection. I have one remote site profile called "Citizens".
Remote Site Name:
Citizens
CHECK: Enable Remote Site
Network Service:
PPP over ATM (PPPoA)
User Name: xxxxx@citlink.net
Password: yyyyy
VC Parameters:
VPI: 0
VCI: 35
Quality of Service:
Unspecified Bit Rate
UNCHECK: Enable Bridging
CHECK: Enable IP Routing
UNCHECK: Enable IPX Routing
Address Translation:
CHECK: Nat
Default Workstation: 0.0.0.0
Static Ports: (See below)
Routing Information:
CHECK: Use this connection as default gateway
RIP: None
Static IP Routes:
None
Security:
CHECK: Verify packets can be routed back
CHECK: Enable protect files and printers
IPX Stuff:
Turn all this off.
TCP Ports:
21 ftp 192.168.0.2:21
22 ssh 192.168.0.2:22
25 smtp 192.168.0.2:25
80 http 192.168.0.2:80
443 https 192.168.0.2:443
465 smtps 192.168.0.2:465
993 imaps 192.168.0.2:993
1723 pptp 192.168.0.2:1723
UDP Ports:
53 domain 192.168.0.2:53
rpm -i package.rpm # Install a package
rpm -U package.rpm # Update an installed package
rpm -F package.rpm # Freshen (Update only if installed)
rpm -e packageName # Remove a package
rpm -qi # Describe an installed package
rpm -qa # List all installed packages
rpm -qf afile # See which package installed a file
rpm -qR package # Find out what a package needs
rpm -qa --last # List by installation time
rpm -qlp package.rpm
rpm -qai | grep Dist | awk -F': ' '{print $3}' | sort | uniq -c
rpmbuild --rebuild your.src.rpm
The result is in /usr/src/redhat/RPMS/i386
rpm -i xxxx.src.rpm
You can now tamper with the tgz in /usr/src/redhat/SOURCES
rpmbuild -bs /usr/src/redhat/SPECS/xxxx.spec
The result is in /usr/src/redhat/SRPMS
rpmbuild -tb yourpackage.tar.gz
rpm --root mp --initdb
rpm2cpio rpmFile > archive.cpio
cpio -mid < archive.cpio
rpm2cpio rpmFile | cpio -mid
The whole format is one "string" Each tag specification looks like this: %{NAME} You usually want a newline at the end:
rpm -q xmms --qf "%{SIZE}\n"
Between the "%" and the opening brace "{" you can specify field sizes, or any other C printf formatting chars. Positive integers select right alignment in the field. Negative integers select left alignment in the field:
rpm -qa --qf "%-30{NAME} %10{SIZE}\n"
Some header tags select arrays of values. Use square brackets to iterate over the set. You can specify more than one array tag inside the query:
rpm -q xmms --qf "[%-50{FILENAMES} %10{FILESIZES}\n]"
Normally, all tags inside square brackets must be array tags. If you want to print a fixed tag as a label on each line, add an "=" char to the fixed-tag name:
rpm -q xmms -qf "[%{=NAME} %{FILENAMES}\n]"
Display a list of all rpms sorted by size:
rpm -qa --qf "%-50{NAME} %10{SIZE}\n" | sort -nk 2,2
Display a list of all "devel" packages sorted by size:
rpm -qa | grep devel | \
xargs rpm -q --qf "%-50{NAME} %10{SIZE}\n" | \
sort -nk 2,2
rpm --querytags
rpm -q packageName --qf "%{SIZE}\n"
rpm -qa | grep devel | xargs rpm -q --qf "%{NAME} %{SIZE}\n"
Symptom: All rpm commands "hang up"
Find and kill all processes running rpm or up2date:
ps ax | grep rpm
ps ax | grep up2date
(Kill them by hand)
Remove all rpm database lock files:
rm -f /var/lib/rpm/__db*
This usually gets things going. If not:
First make a backup of the database:
cp -a /var/lib/rpm /var/lib/rpm.copy
Then rebuild the database
rpm --rebuilddb
This takes some time, but if it hangs forever, repeat the "Find and kill rpm" step and proceed with:
cd /var/lib/rpm
db_verify Packages
(You may need to install db4-utils)
If db_verify reports errors, try:
cp Packages Packages.backup
db_dump Packages.backup | db_load Packages
rpm --rebuilddb
If all these steps fail, you are in big do-do.
Recent versions of Redhat require signature verification when processing packages. If you havn't imported the Redhat GPG signature, you will get errors of the form:
warning: ... V3 DSA signature: NOKEY, key ID ...
To fix this, first obtain a copy of the file RPM-GPG-KEY. If you are creating your own rpm-based distribution, the file is widely available on the web.
On a Redhat system, it can be found using:
find /usr -name RPM-GPG-KEY
When you have the file, execute the following expression:
rpm --import RPM-GPG-KEY
rpm -Va
The code letters: S file Size differs M Mode differs (includes permissions and file type) 5 MD5 sum differs D Device major/minor number mis-match L readLink(2) path mis-match U User ownership differs G Group ownership differs T mTime differs c A configuration file
A streamlined report that ignores date-only changes:
rpm -Va | grep -v ".......T"
To make this a cron job that mails the result:
rpm -Va | grep -v ".......T" | mail myself@mydomain
To skim off acceptable changes
rpm -Va | grep -v ".......T" | grep -vf rpmChanges | \
mail myself@mydomain
Append any new acceptable changes to the rpmChanges file.
smbclient -L server.somewhere.com -U%
smbclient -L server.somewhere.com -U myUserName%myPassword
smbpasswd -a NewUserName
smbpasswd -x NewUserName
pbedit -L
[global]
workgroup = WORKGROUP
netbios name = SERVER
security = user
map to guest = bad user
[homes]
comment = Home Directories
valid users = %S, %D%w%S
browseable = Yes
read only = No
inherit acls = Yes
[global]
...
printing = cups
printcap name = cups
load printers = yes
cups options = raw
[printers]
comment = All Printers
path = /var/tmp
printable = Yes
create mask = 0600
browseable = No
[print$]
comment = Printer Drivers
path = /var/lib/samba/drivers
write list = root
create mask = 0664
directory mask = 0775
[myshare]
path = /mnt/something
browseable = yes
writable = yes
[global]
...
usershare path = /var/lib/samba/usershares
usershare max shares = 100
usershare allow guests = yes
usershare owner only = no
net usershare add myShareName /some/path
\\myHost\myShareName
net usershare delete myShareName
net usershare list
net usershare info
testparm
cd /etc/samba
mv smb.conf smb.conf.backup
testparm -sv > smb.conf.defaults
mv smb.conf.backup smb.conf
sane-find-scanner
For this example, we will assume that /dev/sg0 is the result.
useradd saned
chown root:saned /dev/sg0
chmod g+rw /dev/sg1
sane-port 6566/tcp saned # SANE network scanner daemon
service sane-port
{
socket_type = stream
server = /usr/sbin/saned
protocol = tcp
user = saned
group = saned
wait = no
disable = no
}
You will need to verify the location of the saned program on your system. Use "which saned" and modify the xinet.d file shown above appropriately.
Edit:
/etc/sane.d/saned.conf
Append your allowed hosts (names, ip numbers, or subnets) Example for a local subnet:
192.168.1.0/24
This is not strictly necessary, but it may prevent some module loading errors. Edit:
/etc/sane.d/dll.conf
Remove everything but the entry for your scanner type and "net." The "v41", for example, causes the char-major-81 error.
UPDATE: None of this section applies to Fedora core II.
service xinetd restart
Most of the search command use patterns that are described in the section [Regular Expressions[(#Regular Expressions)
grep pattern file
grep -i pattern file
grep -r pattern startDirectory
grep -ri --include="*.txt" pattern startDirectory
find startDirectory -name pattern
If startDirectory isn't specified, find starts in the current directory. By default, the search looks recursively down into all subdirectories.
The pattern usually contains one or more * wildcards.
You can pipeline the output of find directly to any command that acceptss a stream of filenames. For example:
find path | grep <pattern>
This is equivalent to "grep -r pattern path"
find startDirectory -name "pattern" -exec command arguments \;
The arguments are passed to the command. You can insert the matched filename anywere among the arguments using {}. For example, to make an extended directory listing of files with the extension "mp3":
find -name *.mp3" -exec ls -l {} \;
You can use -ok instead of -exec to get a prompt to confirm the operation for each file.
You can stream filenames to xargs as an alternative to -exec:
find startDirectory -name pattern | xargs <command>
When using xargs, the file name always appears after the command, so this form is less general than using -exec.
Example: Change the permissions on all mp3 files at or below the current directory:
find -name *.mp3 | xargs chmod 644
The example above will fail if the file names contains spaces. (Which music files often do.) To deal with that, we pipeline the file names though a sed expression that puts quotation marks around each name:
find -name *.mp3 | sed 's/^.*$/"&"/' | xargs chmod 644
Finding specific file types
The find command has a "-type t" option where t is one of:
d Directory
f Regular file
... Many others
Unlike "find", The locate command depends on a database updated by a system service that runs periodically. On most linux systems, this is done daily. Consequently, locate only finds files created on previous days. By using a database, locate is much faster than find, especially when you have no idea where to look for the file.
Basic form:
locate pattern
For example, if you are looking for files that contain the string "resolv.conf" anywhere in their name:
locate resolv.conf
In other words, locate works "as if" you had used:
locate *resolv.conf*
which command
Sed operates on files or streams that contain lines of text. The output is the result of applying a command to lines that match a pattern. By far the most common commands are substitution and deletion.
Sed has a well-deserved reputation for being a write-only programming language. There are entire books and many web sites devoted to sed. Some specialize in demonstrating unbelievably obscure expressions.
Most of the effort to master Sed is associated with learning to write pattern expressions. The introductory sections that follow cover the basics. After the introduction, 15 examples are presented. If you take time to understand them, you will become reasonably proficient.
Most of the examples shown below can be tested by sending through a single line:
echo 'test string' | sed 'some expression'
Some examples only make sense when applied to a whole file. In those cases you can test the expression using one of these forms:
cat testFile | sed 'some expression'
Or:
sed 'some expression' testFile
sed 'expression' infile >outfile
sed 'expression' <infile >outfile
echo "some text" | sed 'expression'
sed -e 'expression1' -e 'expression2'
Or the shorter form:
sed 'expression1;expression2;'
A sequence of sed expressions can be stored in a file. Each line of the file is a sed expression without the bounding quotes. The script file may contain comments that begin with "#" as in a bash script. Usage:
sed -f scriptFile inputFile
Or:
cat inputFile -f scriptFile
Patterns may be string literals, character sets or special symbols. Special symbols must be escaped using a backslash:
? $ . [ ] \ / ^
Common patterns:
mystring - A literal
^ - Beginning of the line
$ - End of the line
. - Any single character
\n - Newline
.* - Zero or more characters
.+ - One or more characters
.? - Zero or one characters
(The * + or ? may be used after any construct)
Grouping is done using parentheses:
(abc)+ - One or more instances of abc
(a \| b) - a or b
Character sets:
[pqr] - Any one of p q or r
[a-z] - Any lower case letter
[^a-z] - Any non lower case letter
[a-z]* - Any number of lower case letters
[a-zA-Z]* - Any number of mixed lower and upper case letters
Character classes and their equivalent sets:
[[:alnum:]] - [A-Za-z0-9] Alphanumeric characters
[[:alpha:]] - [A-Za-z] Alphabetic characters
[[:blank:]] - [ \x09] Space or tab characters only
[[:cntrl:]] - [\x00-\x19\x7F] Control characters
[[:digit:]] - [0-9] Numeric characters
[[:graph:]] - [!-~] Printable and visible characters
[[:lower:]] - [a-z] Lower-case alphabetic characters
[[:print:]] - [ -~] Printable (non-Control) characters
[[:punct:]] - [!-/:-@[-`{-~] Punctuation characters
[[:space:]] - [ \t\v\f] All whitespace chars
[[:upper:]] - [A-Z] Upper-case alphabetic characters
[[:xdigit:]] - [0-9a-fA-F] Hexadecimal digit characters
To simply print lines that contain a pattern:
sed -n '/pattern/p'
The -n tells sed to only print lines that contain the pattern. By default, sed will print every line.
A basic principle of sed is the phrase: "On each line". Consider that a prefix to each comment below.
Substitute only the first instance of old with new:
sed 's/old/new/'
Substitute all instances of old with new:
sed 's/old/new/g'
Substitute 3rd instance of old with new:
sed 's/old/new/3'
Substitute old with new on lines that contain red:
sed '/red/s/old/new/g'
Remove leading whitespace:
sed 's/[ \t]*//'
Remove trailing whitespace:
sed 's/[ \t]*$//'
Delete lines that contain a pattern:
sed '/pattern/d'
Output lines that contain a pattern:
sed '/pattern/!d'
Delete all blank lines:
sed '/^$/d'
Delete extra blank lines (multiple to one)
sed '/^$/N;/^\n$/D'
The "&" symbol inserts the whole pattern matched:
Add a prefix to every line:
sed 's/.*/myPrefix&/'
Add a suffix to every line:
sed 's/.*/&mySuffix/'
Put quotes around a line:
sed 's/^.*$/"&"/'
Quoting lines is great for processing file names that may contain spaces:
find * -name *.mp3 | sed 's/^.*$/"&"/' | xargs chmod 644
(Change the ownership of all mp3 files.)
The literal values matched in pattern expressions may be captured in escaped parenthesis:
\(any pattern\)
Multiple capture groups may be used. On the substitution side, the value of each capture group may be inserted:
\1 for the first capture
\2 for the second capture, etc.
The expression:
echo "his name was Fred" | sed 's/his name was \(.*\)/Name: \1/'
Produces:
Name: Fred
Sed normally edits the input text and outputs new text. If you want the new text to replace the old text in an existing file, use -i to modify the input file. For example, to make a global substitution in multiple text files:
sed -i 's/oldThing/newThing/g' *.txt
It is wise to preview the change on one file before using -i. It is wise to use -b on Windows to prevent the files from being converted to Unix line terminator format.
The 23rd line:
sed '23q;d'
The last line:
sed '$!d'
Number the lines:
sed = myfile.txt | sed 'N;s/\n/\t/'
Reverse the order of lines:
sed '1!G;h;$!d'
Remove trailing blank lines:
sed ':a;/^\n*$/{$d;N;ba;}'
Append a final blank line:
sed '$G'
Script to 'normalize' trailing blank lines in place:
sed -i ':a;/^\n*$/{$d;N;ba;}' myfile
sed -i '$G' myfile
Whenever I install a new Linux system, I always try to see how long I can live with SELinux. I know it's a really good idea. Especially on an internet-facing server. My record is 4 days.
Edit: /etc/selinux/config
Change: SELINUX=disabled
Reboot.
This is only necessary if the little dot that appears after the file permissions when running "ls -l" really bothers you:
find / -print0 | xargs -0 -n 1 setfattr -h -x security.selinux
Obviously, you shouldn't do this if you ever plan to turn on SELinux.
If you're sure the warning is from something ok, proceed:
cat /var/log/audit/audit.log | audit2allow -M results
This will produce two files:
results.pp
results.te
Review the contents of results.te: In some cases, you simply have to restore a label. Specific instructions are given.
If new rules are required, run:
semodule -i results.pp
The lm_sensors package handles all motherboard temperature sensors. The command line program is:
sensors
To see a continuous temperature monitor that updates every 2 seconds:
watch -n 2 sensors
SysVinit is the old way of managing system services. Systemd is the new way of managing system services. Most linux distributions provide an emulation layer so users familiar with SysVinit can work in a familiar way.
See the section "Systemd" following this one (Services).
Services or 'daemons' are programs that run in the background, usually without any user interaction.
They implement system functions such as logging, network servers, and many other housekeeping tasks.
To start a service by hand:
service <serviceName> <selector>
Typical selectors are: start, stop, restart, status.
If you run the command without a selector, it will display a list of possible selectors.
The operating system can run in different modes called run levels. Each runlevel determines a set of services to run and a set of services to stop.
Run levels are identified by small integers. The group of services associated with each run level is conventional:
0 Halt
1 Single user
2 Multiuser, no networking, local additions
3 Multiuser, networking, local additions
4 Multiuser, networking, no local additions
5 Same as 3 plus X Windows Login
6 Reboot
who -r
telinit newLevelNumber
This is done by editing the file:
/etc/inittab
Inside, you will find an expression that looks like this:
id:3:initdefault::
In the example shown above, "3" is the run level used at boot time. If you wanted to have an X-Windows splash screen with a login dialog, you would change this number to "5".
For each runlevel, we need to specify which services start and which services stop. We also need to specify the order in which services start or stop to allow for interdependencies.
A collection of directories and symbolic links are used to perform these functions. The Linux boot process uses these links to start or stop the appropriate services at boot time or when you explicitly switch the run level.
A directory exists for each run level X:
/etc/rc.d/rcX.d
Each run level directory contains symbolic links. The links all point to the service control files found in:
/etc/rc.d/init.d
The name of the link begins with the letter "S" if the service should start. The name of the link begins with "K" if the service should stop. (Think "killed.") The start and stop links for a given service point to the same file.
The link names also determine the order of starting or stopping: Following the S or K is a two-character integer that determines the order of execution relative to the other links in the directory. Higher numbers make the service start later.
After the ordering digits, the service name appears. For example, the following link will start networking at relative step 10 of runlevel 3:
/etc/rc.d/rc3.d/S10network -> ../init.d/network
Networking gets turned off in runlevel 1, so we find this link:
/etc/rc.d/rc1.d/K90network -> ../init.d/network
When a service is installed, a start or stop link should should be created in every run level directory. Here's a complete example for the web server httpd:
Starting: /etc/rc.d/rc3.d/S85httpd -> ../init.d/httpd /etc/rc.d/rc4.d/S85httpd -> ../init.d/httpd /etc/rc.d/rc5.d/S85httpd -> ../init.d/httpd
Stopping: /etc/rc.d/rc0.d/S15httpd -> ../init.d/httpd /etc/rc.d/rc1.d/S15httpd -> ../init.d/httpd /etc/rc.d/rc2.d/S15httpd -> ../init.d/httpd /etc/rc.d/rc6.d/S15httpd -> ../init.d/httpd
It is important idea to keep the links complimentary: If you create start links on levels 2 and 5, you should create kill links on levels 0,1,3,4, and 6.
It is clearly a pain to do all this correctly by hand.
The chkconfig command helps you maintain run level links. It doesn't start or stop services, it only creates or deletes the appropriate symbolic links in the run level directories.
The chkconfig command obtains run level and starting order information from a special comment found inside each service control file. A typical comment in a service control file looks like this:
# chkconfig: 2345 90 60
This was extracted from my /etc/rc.d/init.d/crond control file. The comment suggests that the crond service should start on runlevels 2345 at relative position 90. By the complimentary priciple, it should have kill links on levels 0, 1 and 6 at relative position 60.
Install both start and kill links for a newly installed service:
chkconfig --add serviceName
Remove all start and kill links for a service at all run levels.
chkconfig --del serviceName
Some service control files will have a minus character for the list of run levels. For example, my Samba control file (smb) contains:
# chkconfig - 91 35
To install a new service like this you first use:
chkconfig --add serviceName
This will put kill links on every level.
Then you specify the levels where you want the service to run:
Add start links and remove kill links from specified levels:
chkconfig --level levelString serviceName on
Add kill links and remove start links from specified levels:
chkconfig --level levelString serviceName off
If you don't use the "--level levelString" option, the default levels 2345 will be used.
Example to start Samba at runlevels 345:
chkconfig --level 345 smb on
It often happens that people try to maintain the links by hand and get everything messed up. To clean house when you are uncertain about a service configuration, first get rid of all the links using:
chkconfig --del serviceName
yum install smartmontools
smartctl -i /dev/sda
smartctl -s on /dev/sda
smartctl -c /dev/sda
smartctl -t short /dev/sda
smartctl -t long /dev/sda
smartctl -l selftest /dev/sda
smartctl -H /dev/sda
smartctl -a /dev/sda
smartctl --nocheck standby -i /dev/sda | grep "Power mode"
Not spinning modes:
OFF
SLEEP
STANDBY
Spinning modes:
IDLE
ACTIVE
To send fault notices by email, sendmail or exim must be installed:
dnf install exim
Edit /etc/aliases to forward root email to yourself.
Start and enable the service:
systemctl enable --now smartd
The default configuration will scan all the disks every 30 minutes unless they are in standby. If smartd encounters the same disk in standby 10 times in a row, it will wake it up and scan anyway.
http://commons.oreilly.com/wiki/index.php/SpamAssassin
Be sure to log in as yourself. (not root!) Train with more ham than spam.
sa-learn --no-sync --spam --mbox <mboxFile>
sa-learn --no-sync --ham --mbox <mboxFile>
sa-learn --sync
sa-learn --dump magic
~/.spamassassin/user_prefs
/etc/mail/spamassassin/local.cf
required_hits 5.0
use_bayes 1
use_pyzor 1
use_razor2 1
bayes_auto_learn 1
allow_user_rules 1
ok_locales en ja
report_safe 0
allow_user_rules 1
whitelist_from someone@somewhere.com
whitelist_from *@mycompany.com
blacklist_from someone@somewhere.com
blacklist_from *@badguys.com
header H_NINJA_1 From =~ /\.ninja/i
score H_NINJA_1 10.0
describe H_NINJA_1 From server contains dot ninja
header H_002 Subject =~ /acne/i
score H_002 0.5
describe H_002 Acne cures
body H_UNLIM /Get Unlimited access/i
score H_UNLIM 0.5
describe H_UNLIM Get Unlimited access
spamassassin -D --lint 2>&1 | more
spamassassin -D --lint 2>&1 2> results.txt
spamassassin -t -D < someFile.eml 2>&1
spamassassin -D --lint 2>&1 | grep -i failed
header RCVD_IN_MSPIKE_BL eval:check_rbl('mspike-lastexternal', 'bl.mailspike.net.')
tflags RCVD_IN_MSPIKE_BL net
score RCVD_IN_MSPIKE_BL 3.5
header RCVD_IN_MSPIKE_WL eval:check_rbl('mspike-lastexternal', 'wl.mailspike.net.')
tflags RCVD_IN_MSPIKE_WL net
score RCVD_IN_MSPIKE_WL -2.1
Examples only. Not recommendations.
score RCVD_IN_SORBS_ZOMBIE 3.5
score RCVD_IN_SORBS_DUL 2.5
score URIBL_RHS_DOB 3.8
sa-learn --backup >myState.sadatabase
sa-learn --restore myState.sadatabase
sa-learn --clear
systemctl
systemctl status foo
systemctl start foo
systemctl stop foo
systemctl restart foo
systemctl enable foo
systemctl disable foo
systemctl enable --now foo
systemctl is-enabled foo.service; echo $?
The value returned is a script status:
0 => enabled
1 => disabled
Systemd uses "targets" instead of runlevels.
Some retro symbolic links are provided as well:
runlevel3.target -> multi-user.target
runlevel5.target -> graphical.target
systemctl isolate multi-user.target
systemctl isolate graphical.target
systemctl get-default
systemctl set-default <target>
Systemd Old SysV
------------------------
poweroff 0
rescue 1
multi-user 3
graphical 5
reboot 6
systemctl list-units
systemctl list-units --state=failed
systemctl list-units --state=active
This will open a blank file where you can add lines or override exiting lines in an existing service file:
systemctl edit foo
Note that some systemd script directives are incremental. For example, to modify the "ExecStart" line, your modification file must first clear the old definition:
ExecStart=
ExecStart=your new version
When you exit the editor, it will create a new directory and file:
/etc/systemd/system/foo.service.d/override.conf
Exiting the editor will also cause systemd to reload the modified script as if you had executed:
systemctl daemon-reload
To remove the effect of making an incremental change, remove the entire directory:
rm -rf /etc/systemd/system/foo.service.d
And reload the scripts:
systemctl daemon-reload
This will open the existing script in an editor session:
systemctl edit --full foo
When you exit the editor, a override script file will be created in:
/etc/systemd/system/foo.service
Exiting the editor will also cause systemd to reload the modified script as if you had executed:
systemctl daemon-reload
To undo the effect of this edit, simply remove the file:
rm /etc/systemd/system/foo.service
And reload the scripts:
systemctl daemon-reload
Because it's a little hard to see what you're doing with an incremental change, you might consider using --full all the time. The reason for not doing that is the possibility that there are other incremental modifications for the same script. In that case, your change should be included with the others, rather than replacing the entire unit file. Check for this possiblitiy by examining the files in:
/etc/systemd/system
As the name suggests, these are services that regular users can control.
The service file "myThing" (for example) must be installed by root to the path:
/usr/lib/systemd/user/myThing.service
After that, any user can execute:
systemctl --user start myThing
systemctl --user stop myThing
systemctl --user enable myThing
etc.
Services enabled by a user will start when the user logs in and stop when the user logs out.
The log entries for a user service can be displayed:
journalctl -b --user-unit myThing
Copy files to and from remote hosts. An ssh relationship must be configured before using scp. (see next section)
Copy a remote file to a local directory:
scp user@remoteIP:remoteFile localDirectory
Copy a local file to a remote directory:
scp localFile user@remoteIP:/remoteDirectory
Entire directories can be copied using -r:
scp -r localDirectory user@remoteIP:remoteParentDirectory
Copy files between two remote hosts:
scp sourceUser@sourceIP:sourcePath destUser@destIP:destPath
The general syntax is:
scp srcUser@srcMachine:srcFilePath destUser@destMachine:destFilePath
If the path names are not absolute, they are relative to the login directories for the designated users.
Secure Shell (ssh) lets you connect to a remote host
and start a shell session just like Telnet.
Setting up ssh access is conceptually involved, but once this is done, ssh is very easy to use. For example: To start a shell session on a remote host you simply type:
Login using your current user name:
ssh remoteHostIpName
Specify the remote user name:
ssh -l userName remoteHostIpName
Or use 'email' notation:
ssh userName@remoteHostIpName
You can run a command on a remote system and see the results locally:
ssh userName@remoteHost ls
SSH can perform many other marvels such as port forwarding: This lets you channel tcp/ip traffic between any selected client and server port through the secure connection. A common use of this feature is to run remote X-Windows programs and have them display on the client automatically.
The following sections deal with understanding and configuring basic ssh access.
SSH supports several encryption mechanisms, but one of the best is based on the RSA public key system.
To use RSA, you need a pair of numerical keys. One key is public: You can pass it out to your friends or publish it in a public directory. The other key is private and must be keep secret.
RSA is a Good Thing™ because it works without ever exchanging private keys over an insecure communication channel, e.g. the internet. It also supports signatures: A person who recieves a message can verify that only you could have sent the message.
Home directory and set restricted permissions:
mkdir .ssh
Or using numerical permissions:
chmod 700 .ssh
Run ssh-keygen to create your public and private key files.
ssh-keygen -t rsa -C "A comment"
The program will propose default filenames for your, public and private key files, which you should accept:
/home/yourName/.ssh/id_rsa
/home/yourName/.ssh/id_rsa.pub
You will also be asked for a passphrase. If you specify a passphrase, you will need to enter it whenever ssh or other programs want to use your private key.
The comment parameter is optional. If you don't supply a comment using "-C", the default is a string derived from your login name and the name of your host formatted like an email address:
yourName@yourMachine.yourDomain
The comment appears as plain text in your public key string. When examining an authorization file on a remote server, this text helps you remember who is authorized.
Once you have a key set, you can freely distribute copies of your id_rsa.pub file to anyone who wants to send you secure messages.
The ssh-keygen program will create the .ssh directory and key files with the correct permissions. But sometimes things get messed up. These commands will fix everything:
cd ~/
chmod u=rwx,g-rwx,o-rwx .ssh
cd .ssh
chmod u=rw,g-rwx,o-rwx id_rsa
chmod u=rw,g=r,o=r id_rsa.pub
Or if you're of the old school:
cd ~/
chmod 700 .ssh
cd .ssh
chmod 600 id_rsa
chmod 644 id_rsa.pub
You must setup your client ssh keys as decribed above. They will be in the hidden .ssh directory in your home directory on the client machine.
Email, ftp or otherwise copy your id_rsa.pub file to your home directory on the remote machine. To avoid confusion, we rename the file "client_rsa.pub".
You must append the contents of this file to the authorized_keys file in the .ssh directory at the top-level of your remote home directory.
To do this, you need to log into your remote account by some other means or ask someone who has access to do this for you. This command will append your key to the authorized_keys file:
cat client_rsa.pub >> .ssh/authorized_keys
If you're creating a new .ssh/authorized_keys file, you must set the permissions or remote access will be denied:
chmod u=rw,g-rwx,o-rwx .ssh/authorized_keys
If some other user such as "root" does this for you, they also need to make sure that you own the file:
chown yourName:yourGroupName .ssh/authorized_keys
Similarly, the remote .ssh directory must have the correct permissions and owner:
chmod u=rwx,g-rwx,o-rwx .ssh
chown yourUserName:yourGroupName .ssh
Here's a quick check on how the .ssh directory should look:
ls -ld .ssh
drwx------ 2 you you 4096 2008-02-27 13:58 .ssh
ls -l .ssh
-rw------- 1 you you 1727 2007-08-04 07:15 authorized_keys
-rw------- 1 you you 887 2004-07-16 03:48 id_rsa
-rw-r--r-- 1 you you 221 2004-07-16 03:48 id_rsa.pub
-rw-r--r-- 1 you you 2553 2008-02-25 10:55 known_hosts
The above listing shows the known_hosts file, which is automatically created and/or updated whenever remote clients connect to this account.
With ssh configured properly, you don't need to remember or type passwords when logging into a remote system. To achieve this marvel, edit:
/etc/ssh/sshd_config
Find this keyword and change the value as shown:
PasswordAuthentication no
By adding a "config" file to your .ssh directory, different configuation options and defaults can be set for each host you commonly use. Here is an example .ssh/config file:
Host someserver.somewhere.com
User myusername
ForwardX11 yes
ForwardX11Trusted yes
Host otherserver.elsewhere.com
User otherUserName
...
By specifying a username as shown above, the command line for remote login becomes very simple:
ssh somewerver.somewhere.com
Most of the options you can specify system-wide for the ssh client in /etc/ssh/ssh_config may alternatively go in your local .ssh/config file, elminating the need to modify the system defaults.
Permissions for the config file should be 644.
If your linux system is running inside a virtualmachine, you'll need to add an option the the .sss/config file for all users on that machine:
Host *
IPQoS=throughput
Without this fix, you'll see this error when you try to connect to a remote machine:
client_loop: send disconnect: Broken pipe
An entire host machine may have a key set. The public part of this key is kept on remote servers to authorize access by the entire machine. Many services can be configured to use host-level authorization.
Host keys should be located in:
/etc/ssh/ssh_host_rsa_key
/etc/ssh/ssh_host_rsa_key.pub
The automatic installers for many Linux distributions create the host key files in /etc/ssh automatically.
To create them by hand, run ssh-keygen and specify the path names shown above. Passphrases are not normally used with host keys.
svnadmin create myproject
svn import [localDirectory] repoURL
svn checkout repoURL [localDir]
svn status
svn log
Note: The "svn log" won't list your most recent
commits until you perform an "svn update".
Many subversion GUI clients do this automatically
after each commit.
svn list ^/MyPath
The path can be anything that exists, but usually
begins with things like trunk, branches or tags.
svn diff <optional filename>
svn revert
svn revert aFile
svn add aFile
svn rm aFile
svn mv fromPath toPath
svn mkdir aDirectory
Each comment bumps the revsion number;
svn commit -m "This is why I did the deed."
svn update
svn log -r {2006-11-20}:{2006-11-29}
svn blame aFile
svn copy ^/trunk ^/tags/MyTagName -m "Why I did this"
svn copy ^/trunk ^/branches/MyBranchName -m "Why I did this"
svn switch ^/branches/MyBranchName
svn list ^/branches
svn list ^/tags
svn merge ^/trunk
svn merge ^/branches/MyBranchName
Ideas about using --reintegrate and closing out a
branch are obsolete. You can work on a branch after
after merging it to trunk. Everything just works.
After running "svn update", sometimes conflicts are reported.
Display a summary of possible actions:
svn resolve
Accept your changes as they were before running "svn update":
svn resolve --accept mine-full
Accept the changes brought in by "svn update":
svn resolve --accept theirs-full
The resolve command also accepts an optional path, so you can restrict the action to a particular file.
svn resolve --accept mine-full source/goop.c
Keywords
BASE - Version in your working copy as of your last commit.
HEAD - Most recent version in the remote repository.
COMMITTED - The most recent revision <= BASE, in which an item changed.
PREV - (COMMITED - 1)
Show the last change committed to foo.c
svn diff -r PREV:COMMITTED foo.c
Show the log message for the latest repository commit
svn log -r HEAD
Compare your working copy to the latest version in the repository
svn diff -r HEAD
Compare the unmodified version of foo.c with the latest version of foo.c in the repository
svn diff -r BASE:HEAD foo.c
Show all commit logs for the current versioned directory since you last updated
svn log -r BASE:HEAD
Rewind the last change on foo.c, decreasing foo.c's working revision
svn update -r PREV foo.c
Compare the unmodified version of foo.c with the way foo.c looked in revision 14
svn diff -r BASE:14 foo.c
Compare base and working copy ignoring whitespace and newlines
svn diff myThing -x --ignore-eol-style -x --ignore-all-space
This must be done on a per-repository basis on the server. I like to make the change in my template repository, which I simply copy when starting new projects.
cd /var/www/svn/yourRepoName
ls
You should see top-level directories: conf, dav, db, hooks, locks.
cd hooks
cp pre-revprop-change.tmpl pre-revprop-change
chmod a+x pre-revprop-change
The hook scripts must be "runnable" which means that the volume itself must have execute permissions. Some website operators like to mount the /var/www directory on volume with execute permission disabled. If you prefer that arrangement, the /var/www/svn directory must be mounted on another volume. This is easy to do if you run some kind of volume management software: LVM, ZFS, etc.
If the svn server root is at /svn and your project repository is in /svn/MyProject: (This is the server location of your project database, not one of your checkouts.)
cd /svn
svnadmin dump MyProject > MyProject.svndump
cd /svn
rm -rf MyProject # If there's an old one there.
svnadmin create MyProject
svnadmin load MyProject < MyProject.svndump
svn switch --relocate http://old.server.com/svn/myproject http://new.server.com/svn/myproject
Edit:
~/.subversion/servers
Change:
store-plaintext-passwords=yes
When the value is "no", you will always be prompted
for a password, but the server and username will be cached.
See next section.
edit
~/.subversion/auth/svn.simple/<bunch of hex digits>
Remove these three lines
password
V 7
yourPassword
su <username>
sudo -i
visudo
xxxx ALL=(ALL) NOPASSWD:ALL
aspell -c myFile.txt
echo $1 | ispell -a | sed -n -e '/^\&/p' -e '/^\#/p'
Put this expression in a shell script on your PATH.
cut -c n-m path
cut -c n- path
tac myfile.txt > myfileReversed.txt
Remember this by "tac" = "cat" reversed.
Get time from a remote server:
rdate -u -p -s ns.scruz.net
Or more simply:
ntpdate ns.scruz.net
Then move it into hardware:
hwclock --systohc
You can also pull the time out of hardware to set the system clock:
hwclock --hctosys <opt>
The <opt> may be --localtime or --utc. For localtime, you
need to have an /etc/localtime file which can be a copy or
link to zoneinfo file. (These are in /usr/share/zoneinfo)
It's also possible to apply an incremental adjustment to the clock:
hwclock --adjust
The startup scripts normally do something like this:
hwclock --hctosys
hwclock --adjust
Examples using a specific time:
at 10:25pm
at 1am Dec 20
at 2pm tomorrow
at midnight tomorrow
Examples using relative time:
at now + 10 minutes
at 4pm + 3 days
at 4pm + 3 weeks
A prompt will appear for you to enter commands. Finish with EOF (control D)
Show your pending jobs:
atq
Remove a job:
atrm <job number>
Send a reminder to your cellphone
at 6am Mar 17
mail -s "Meeting at 10am in Room 101" 1234567890@attnet.com
Don't forget to bring the rats!
^D
at 3am <<-EOF
service tomcat restart
EOF
timed -M -F localhost
timed
Use a bash script in one of these directories:
cron.daily
cron.hourly
cron.monthly
cron.weekly
Each user has a private crontab file. On Redhat/Fedora systems the file is created with this path:
/var/spool/cron/username
The file won't exist until a cron job is scheduled.
To edit your crontab file:
crontab -e
Crontab file format:
Min(0-59) Hour(0-23) Date(1-31) Month(1-12) Day(0-6 Sun-Sat) Command
Use a * character for "every." This command lists the root directory to a a file at 9AM every Monday:
0 9 * * 1 ls /root > /root/listing.txt
passwd
chsh
shutdown -r now
shutdown -h now
useradd userName
userdel name
In Redhat Land, useradd also creates and adds the new user to a new unique group with the same name.
groupadd name
groupdel name
passwd
passwd user
gpasswd -a userName groupName
gpasswd -d userName groupName
groups userName
usermod loginName \
-g newLoginGroup
-G newGroup1,...,newGroupN
-l newLoginName
-d newHomeDirectory
-u newUID
Using -G, the user will be removed from any group not listed.
Using -l, the user still has their old home directory.
You can't change the login name of a user who is currently logged in.
See man page for more options.
First, make sure the user is logged out, then:
usermod -l newName oldname
groupmod -n newName oldName
usermod -d /home/newName -m newName
THIS SECTION IS OBSOLETE. Please use ssh instead.
rlogin remoteIP
The .rhosts file must be in the remote login directory. It contains the ipNames of allowed users.
You can add a local username if not the same as remote.
The .rhosts file must have read privilages only for owner.
/etc/xinetd.d/rlogin must not be disabled.
If you want to rlogin from a root account /etc/securetty must have an entry for "rlogin".
Update: This method is obsolete and dangerous. Please see the SSH section for a safe alternative.
Concept: Boot the system using the bash shell as the startup application. This will bypass the usual system initialization and login process. Then run passwd to set a new root password.
The procedure varies depending on the boot loader. Example using Grub:
Hit "e" on the boot menu. Select the line that begins with "kernel" Hit "e" again. Add this string to the end of the line:
init=/bin/bash
Press "Enter", then "b" to boot the system. At the bash prompt:
mount /proc
mount / -o rw,remount
passwd
At this point, you will be prompted to enter a new password. Next, remount the root file system read-only to flush the cache:
mount / -o ro,remount
Now control-alt-delete to reboot.
This is for Gnome3 based desktop environments that use gdm.
Edit: /etc/gdm/custom.conf
Add these lines to the [daemon] section:
AutomaticLoginEnable=true
AutomaticLogin=YOURUSERNAME
This is irresponsible, dangerous and not P.C. - Worse, it's an ugly hack.
Install:
dnf install gnome-python2-gnomekeyring
Create this file:
/usr/lib/systemd/user/keyring.service
With this content:
[Unit]
Description=Thwart the keyring service
After=sound.target
[Service]
ExecStart=python -c "import gnomekeyring;gnomekeyring.unlock_sync(None, 'PASSWORD');"
[Install]
WantedBy=default.target
Login as the user associated with PASSWORD and execute:
systemctl --user enable --now keyring.service
That will install a shortcut in:
/home/YOURUSERNAME/.config/systemd/user/default.target.wants/
In most environments, the arrow keys work.
j Down one line.
k Up one line.
h Cursor left.
l Cursor right. (lower case L)
<spacebar> Cursor right.
<backspace> Cursor left.
<control>d Down one page.
<control>u Up one page.
$ Go to end of line.
. Go to beginning of line.
G Go to end of file.
1G Go to start of file.
nG Go to absolute line number n.
/pattern/G Go to next line that contains pattern
i Insert text at cursor.
a Insert text after cursor.
<ESC> Leave insert mode.
P Insert last thing deleted.
dd Delete current line.
x Delete current char at cursor.
<bs> Delete previous char.
J Delete line break.
(Join current line with next line)
Marks are denoted by single letters.
The "current line" is the line that contains the cursor.
A selection is a block of lines bounded by a mark and the current line.
ma Set a mark "a" at current line.
d'a Cut lines from mark "a" to current line.
y'a Copy ("Yank")lines from mark "a" to current line.
P Paste deleted or yanked lines before the current line.
V Go to visual mode: move cursor to select lines
then use d or y.
Indenting commands operate on selections as described above.
>'a Indent right from mark "a" to cursor.
<'a Indent left from mark "a" to cursor.
It's easier to use visual mode followed by < or >.
:r <filename> Read in a file at current location.
:w Write everything to current file.
:w <filename> Write everything to selected file.
:w! <filename> Overwrite existing file.
:wq Write current file and quit.
:wq! Write current file and quit. Override protections.
:q Quit but prompt if changes were made.
:q! Quit and don't save changes.
:!<any cmd> Show result of Bash command.
:r !<cmd> Insert result of Bash command.
:s/old/new Substitute irst instance on the current line.
:s/old/new/g Substitute all instances on the current line.
:%s/old/new/g Throughout the whole file
:'a,'bs/old/new Between marks "a" and "b".
:'<,'>s/old/new Inside visual mode selection (V).
:*s/old/new Abbreviated visual mode selection.
. Current line.
$ Last line.
/pattern/ Next line that contains pattern.
\? Next line with previously used pattern.
As a rule, .mkv is a good choice because it handles chapters, multiple
tracks, subtitles, etc. correctly and in a highly portable manner.
ffmpeg -demuxers
To see details about one of the entries listed:
ffmpeg --h demuxer=<entry>
ffmpeg -muxers
To see details about one of the entries listed:
ffmpeg --h muxer=<entry>
Copy the first video, audio, and subitle track without re-encoding:
-c copy
Unfortunately, "-c copy" is rarely satisfactory...
Copy all video, audio, and subtitle tracks with re-encodeing:
-vcodec copy -acodec copy -scodec copy
ffmpeg -i myVideo.flv
ffmpeg -i myVideo.flv -ab 128k myAudio.mp3
ffmpeg -i myVideo.flv -acodec copy myAudio.xxx
You have to specify the audio file extension: xxx: .wav, .mp3, etc.
ffmpeg -i myVideo.avi -vn -ar 44100 -ac 2 -ab 192k -f mp3 mySound.mp3
ffmpeg -i myVideo.mkv -map 0:a:N -c:a aac -ac 2 myVideoStereo.mkv
The value of N selects the audio track (0,1,2...) The output file extension can be a container or a muxing entry of the correct type. In this case, the aac codec goes to a file with extension ".adts"
ffmpeg -i myVideo.flv myNewVideo.xxx
Choosing "xxx" determines the container format.
ffmpeg -i myVideo.xxx -vcodec copy -acodec copy -scodec copy myNewVideo.yyy
xxx and yyy should name any of the well-known containers such as mkv, mp4, etc.
The most flexible result requires using a file that contains the track file names:
mylist.txt
file track1.mp4
file track2.mp4
...
Then use: (for example)
ffmpeg -f concat -i mylist.txt -vcodec copy -acodec copy -scodec copy Result.mkv
ffmepg -codecs
ffmepg -i myVideo.flv -acodec acodec -vcodec vcodec myNewVideo.xxx
ffmpeg -i myVideo.mp4 -i myVideo.en-us.srt -c copy -c:s srt -metadata:s:s:0 language=eng myVideo.mkv
ffmpeg -i myMovie.mp4 -i sub.en.srt -i sub.chi.srt -map 0 -map 1 -map 2 \
-c copy -c:s srt -metadata:s:s:0 language=eng -metadata:s:s:1 language=chi myMovie.mkv
ffmpeg -i myVideo.mkv -c copy -sn myVideoNoSub.mkv
ffmpeg -i input.mkv -c copy -bsf:v "filter_units=remove_types=6" output.mkv
ffmpeg -i myVideo.mkv myVideo.sup
ffmpeg -i myVideo.mkv myVideo.srt
ffmpeg -i myVideo.mkv -c copy -map 0:s:0 myVideo.srt
-c copy Do not convert the selected tracks
-map 0:s:0 First track
-map 0:s:1 Second track
...
This appears to work, but the subtitles are out of sync :-(
ffmpeg -i myVideo.mkv -i mySubtitles.sup -c copy -map 0 -map 1 -metadata:s:s:0 language=eng myResult.mkv
ffprobe -v error -of json myVideo.mkv -of json -show_entries "stream=index:stream_tags=language" -select_streams s
ffmpeg -i input.mp4 -ss beginTime -to endTime -c copy output.mkv
You can omit the "-to" clause to specify the end of the video. The complete time format is:
hh:mm:ss.msec
ffmpeg will perform the cuts at the nearest keyframes.
ffprobe -loglevel error -select_streams v:0 -show_entries packet=pts_time,flags \
-of csv=print_section=0 myVideo.mkv | awk -F',' '/K/ {print $1}'
ffmpeg -i "MyMovie.avi" -vcodec libvpx -acodec libvorbis "MyMovie.webm"
ffmpeg -i myVideo.mkv -c copy -metadata:s:v:0 rotate=90 myNewVideo.mkv
Note: The "rotate" value is absolute. If nothing seems to happen, your video may already be rotated. Try zero first.
ffmpeg -i myVideo.mkv -vf "transpose=N" myNewVideo.mkv
transpose=0 90 Counter-clockwise and vertical flip (default)
transpose=1 90 Clockwise
transpose=2 90 Counter-clockwise
transpose=3 90 Clockwise and vertical flip
To avoid re-encoding the audio, add -codec:a
ffmpeg -i myVideo.mkv myAnimation.gif
ffmpeg -i myVideo.avi -target ntsc-dvd -ps 2000000000 -aspect 16:9 myVideo.mpeg
ffmpeg -i myVideo.avi -target pal-dvd -ps 2000000000 -aspect 16:9 myVideo.mpeg
ffmpeg -i myVideo.avi -target ntsc-vcd myVideo.mpg
ffmpeg -i original.avi -target pal-vcd result.mpg
ffmpeg -i original.mp4 -filter:v scale=720:-1 -c:a copy result.mp4
(The -1 means choose the height to preserve aspect ratio)
ffmpeg -i original.mkv -filter:v "crop=width:height:x:y" result.mkv
mencoder \
-vf rotate=1 \
-ovc lavc -lavcopts vcodec=wmv2 \
-oac copy \
INPUT.avi -o OUTPUT.avi
mencoder \
-vf flip \
-ovc x264 \
-oac pcm \
input.mov -o result.avi
mencoder \
-oac copy \
-oav copy \
-o result.xxx input1.flv input2.xxx ...
startx -- -bpp 24
startx -- -layout myLayout
Layouts are defined in /etc/X11/XF86Config
startx -- -dpi 80 # My Hitachi monitor
startx -- -dpi 95 # My Tecra flat panel
You can do this with a config file .xserverrc in home dir:
exec X -dpi 80
Then just "startx" as usual.
The startx messages are automatically recorded in:
/var/log/Xorg.x.y
If you want to explicity redirect the messages from startx:
startx > myXDebug.txt 2>&1
xdpyinfo
xwininfo
xprop
<Any X command> -display <targetIP>:0
export DISPLAY=targetIPnameOrNumber:0.0
xsetroot -cursor_name left_ptr
Others:
draped_box
hand1
hand2
iron_cross
plus
top_left_arrow
watch
xev
xset -q
xhost +<other machine name or ip number>
Put this command in your .xinitrc to make it permanent
xterm -display <ip>:0 -e <command>
Use FontPath "unix/:-1" (Redhat 6.x)
Update: "unix/:7100" (Redhat 7.x and other Linux systems)
cd theFontDirectory
ttmkfdir > fonts.scale
mkfontdir
chkfontpath --add `pwd`
service xfs reload
Note: Redhat runs ttmkfdir and mkfontdir on every directory known to xfs in the xfs startup script. These fonts become known when you run chkfontpath.
Put the new font file in: /usr/share/fonts
Or in the per-user directory: ~/.fonts
Then run:
fc-cache <directory>
xlsfonts
fsinfo -server unix/:-1
:0 local /usr/X11R6/bin/X
xvinfo
yum install kmod-nvidia
You need to edit a bunch of files on the server:
In the file:
/etc/X11/xdm/kdmrc
Make sure access is enabled as shown:
Enable=true
In the file:
/etc/X11/xdm/Xaccess
Comment out the line:
* CHOOSER BROADCAST #any indirect host can get a chooser
Add lines to the end of the file with the ip name or number of each client:
myclient.my.domain.com
anotherclient.anotherdomain.com
etc.
Note: If you use ip numbers, they must be reversable to names. You can do this by adding a definition to hosts or by running dns.
In the file
/etc/X11/xdm/Xservers
If-and-only-if your server runs headless, comment out this line:
:0 local /usr/X11R6/bin/X
In the file:
/etc/inittab
If you want automatic startup of kdm or xdm, on the server, change the default runlevel:
id:5:initdefault:
In the file:
/etc/rc.d/rc.local
If you don't start kdm using inittab, add this entry to rc.local:
/usr/bin/kdm
In the file:
/etc/sysconfig/desktop
If you have more than one desktop system installed, this entry selects the one that will be used for remote and local logins: (Use KDM for kde or GDM for Gnome.)
DISPLAYMANAGER=KDM
In your iptables firewall setup script you must allow xdmcp:
iptables -A udpChain -p udp --dport xdmcp -j ACCEPT ]]
Newer linux distributions are configured to require SSH authorization for remote X clients. In this document, see "SSH access with RSA keys" for details about creating and using keys.
When using RSA, you still need the ip name or number of each client machine in the server's Xaccess file.
The X server has a file that contains the SSH public keys of each user and/or entire client machines that are allowed to connect:
/usr/share/config/kdm/kdmkeys
If you create this file, you must set the permissions:
chmod u+rw,g-rwx,o-rwx /usr/share/config/kdm/kdmkeys
You don't need to authorize the whole client if you only want to allow selected users on that client.
Public keys are copied or mailed from the client machines. A special public and private key set may be created for the whole host. It is kept in:
/etc/ssh/ssh_host_rsa_key.pub
You append the contents of this file to the server's kdmkeys file to authorized everybody on the whole client.
Public key files for individual users are found in:
/home/someuser/.ssh/id_rsa.pub
Simply append the contents of this file to the server's kdmkeys file to authorize this user.
With all the setup completed, you can login to the remote machine using ssh and run X-Windows programs. The display will be automagically sent back to your machine!
UPDATE: Newer Redhat/Fedora systems need some additional setup on the client side: In the file /etc/ssh/ssh_config you must add these directives:
FORWARDX11 yes
FORWARDX11Trusted yes
Without these changes, you would have to login to the server using ssh with the "-Y" switch to enable access by a trusted host.
DNF. is the successor to yum on Redhat-like distributions.
yum install <packageName(s)>
yum remove <packageName(s)>
yum update
The downloaded files are in /var/cache/yum
yum check-update
yum info <packageName>
yum info repolist
You can edit or create files in:
/etc/yum.repos.d
Alternatively, most yum repositories have and associated rpm file you can install or remove.
Install relative to an alternative root filesystem:
--installroot=<path>
Sometimes different repositories contain packages with conflicting names or build attributes. It is necessary to resolve this to avoid installing or updating with the wrong package. Repositories can be enabled or disabled by editing their yum.repos.d files. Otherwise, these settings can be overridden on the command line:
--enablerepo=<repoName>
--disablerepo=<repoName>
repoquery --whatrequires --installed somePackage
yum deplist somePackage
To get started see: ZFS Without Tears
zpool create myPool sdb sdc sdd sde
zpool create myPool mirror sdb sdc
zpool create myPool raidz sdb sdc sde sde
zpool create myPool raidz2 sdb sdc sde sdd
Specify 4k sectors: -o ashift=12
Don't mount the pool: -m none
zpool export myPool
zpool import
zpool import myPool
zpool import myPool myNewName
zpool import myPool -o altroot=/someDirectory
zpool scrub myPool
zpool clear myPool
zfs create myPool/myDataset
zfs set atime=off myPool/myDataset
zfs set xattr=sa myPool/myDataset
Specify a mountpoint and mount the filesystem:
zfs set mountpoint=/mnt/myMountpoint myPool/myDataset
Specify a legacy mountpoint
zfs set mountpoint=legacy myPool/myDataset
The /etc/fstab entry for a legacy mount point:
myPool/myDataset /mnt/myMountpoint zfs defaults 0 0
The pool itself is a dataset and the "-m path" option is equivalent to:
zfs set mountpoint=path myPool
zfs set mountpoint=none myPool
zfs set compression=on myPool/myDataset
zfs snapshot myPool/myDataset@mySnapshot
zfs rollback myPool/myDataset@mySnapshot
-f : Unmount the file system if necessary
-r : Delete all dependent snapshots
-R : Delete all dependent clones
zfs snapshot myPool/myDataset@now
zfs send myPool/myDataset@now | zfs receive -d myOtherPool
zfs rename myPool/myDataset@now myPoo/myDataset@then
zfs snapshot myPool/myDataset@now
zfs send -i myPool/myDataset@then myPool/myDataset@now \
| zfs receive -uFd myOtherPool
-i : Incremental
-R : Create a replication package with all snapshots and clones
-u : Don't mount anything created on the receiving side
-F : First rollback to the most recent snapshot
-d : Discard pool name from each path element
-x mountpoint : Don't mount any filesystems
zfs send myPool@now | ssh destHost zfs receive -d myDestPool
Enable usershares in smb.conf:
[global]
...
usershare path = /var/lib/samba/usershares
usershare max shares = 100
usershare allow guests = yes
usershare owner only = no
Create the usershares directory by hand
cd /var/lib/samba
mkdir usershares
chmod o+t usershares
chmod g+w usershares
Restart samba and load the shares
systemctl restart smb
zfs share -a
To share a dataset
zfs set sharesmb=on myPool/myDataset
Clients will see the share at
\\myHost\myPool_myDataset
The owner and properties of the myDataset directory on the server must be compatible with access by samba.