Linux
To see help commands do command --help or man command. To paste into PuTTY, use SHIFT + INSERT.
For detailed software and hardware info do apt-get install hardinfo then hardinfo. For CentOS 6 use this.
To write to a user in the same SSH server, do w, get their tty session and then do write user ttySession. If they are root, do write root Session
Awk introduction, If manual.
Binary/binaries
These are normally in the bin folder for a program.
Calendar
apt-get install gcal gcal -K -q GB_EN December/2012-January/2013 # Holidays for Dec/2012 and Jan/2013 with week numbers
Credit to User MPB
Check Linux version/kernel
For Ubuntu do cat /etc/issue or for some CentOS distributions use cat /etc/redhat-release
uname -a uname -r #for just the kernel uname -rs #for OS and kernel
Check if SELinux is enabled
apt-get install chkconfig yum install chkconfig chkconfig --list cat /etc/sysconfig/selinux sestatus selinuxenabled
Check if Virtualization is available for server
CentOS:
egrep '(vmx|svm)' --color=always /proc/cpuinfo
Ubuntu:
apt-get install cpu-checker kvm-ok
CLI/bash Commands and scripting
- The $() syntax allows you to load anything echoed to STDOUT to be loaded into a variable, and the single quotes ensure that if there are any spaces in the directory name, it still gets loaded into a single variable.
- To use command substitution, enclose any command that generates output to standard output inside parentheses and precede the opening parenthesis with a dollar sign, $(command). Command substitution is useful when assigning a value to a variable. It is handy for using the output of one command as an argument to another command.
- Why is $(...) preferred over `...` (backticks)?
- for loop examples
- For variables with multiple pipes "|", use tacs `` instead of quotes ""
- If you have an if statement and its requirements are not met (e.g. greater than) and it then moves onto the next if statement, if it uses a mail function it may send it to the root user's email or the Admin/Administrator's email address. To avoid this use > /dev/null . 2>&1 likely won't work.
- It seems if you are using the read function, you can only call a variable that is inside of it (subshell), from here.
- To stop a ping after x amount of responses, do ping -c x or use ping -oc y (where y equals a maximum amount of tries)
- Use >> to append an output to the end of the file.
- Use [[ instead of [, via http://mywiki.wooledge.org/BashFAQ/031
- If you want a script to make changes to your current shell, not the subshell a bash script works in, execute the script by doing the following (sometimes you may need to do ./ still):
. script
This information was provided by these sources: 1, 2
- The use of && means that you only echo the name of the directory if the directory creation is successful.
$?
This is the exit status/code of the last executed function/program/command.
Awk
To print out a list of just folders/files you want, do;
ls -l filepath | awk '{print $9;}'
This won't work correctly if there is spaces in the filename. To resolve this, use this command whilst in the directory itself.
To do multiple sections of a result, do:
awk '{print $1,$2,$4,$X;}'
If you want to get rid of/cut certain/specific lines/rows from STDOUT aka print a specific line, use awk in this way:
awk 'NR==22'
This is for use without a file. This example will only display the 22nd row from your output.
Notes: Blank lines count as a row. To do multiple lines do awk 'NR==22,NR==25' . This will output line 22-25.
The command sed '22 ! d' would do the same as the awk 'NR==22' example.
Cut
This tool can be used in an example where you get an output but want to strip it to exactly what you need e.g.
lookupipscript.sh <IPaddress>
Output below:
Plan : Bronze, Silver, Gold Type : IPv4 or IPv6 URL : http IP : 0.0.0.0(primary)
lookupipscript.sh <IPaddress> | sed 'row ! d' | awk '{print $column;}'
This would output 0.0.0.0(primary). To get just the IP address and not the "(primary)" section, do:
| cut -c 1-7
Cut counts the first number/letter as 1, not 0.
Find
Find Help (this includes mtime commands)
find . -maxdepth 1 -type f -printf "%f\n" | sed s/,$//
Finds all files that contain "some string". This command is useful in a directory (e.g. mail), so you would do ls -lah | grep year-mm then:
find . -type f -exec grep -l "some string" {} \;
Grep
Do grep for multiple terms (or exclude), do:
grep -v 'chroot\|default\|fs\|fs-passwd\|httpsdocs'
To look for IP addresses, do this courtesy of SO:
grep -E -o '(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)'
Head
If for example you do /var/qmail/bin/qmail-qstat and it prints two separate lines, do this to get just the first line:
head -1
If and Else
Use -f for files, -d for directories
if [ -f $VARIABLE ] then parameters (e.g. echo, mkdir, touch, rm) fi
Combine if and $? to get to do something with the exit status of the last executed command.
if [ $? -eq 0 ]; then commands fi
sed
If you want to get rid of/cut certain/specific lines/rows from STDOUT aka print a specific line, use sed in this way:
sed '22 ! d'
This is for use without a file. This example will only display the 22nd row from your output.
Notes: Blank lines count as a row. The command awk 'NR==22' would do the same.
To print multiple lines do:
sed '22,39 ! d'
To put a variable inside sed, use quotes instead of apostrophes:
sed "22,$variable ! d"
To delete parenthesis/brackets, use this:
sed 's/[()]//g'
sed 's/[)]//g'
sed 's/[(]//g'
sed 's/[[]]//g'
sed 's/[]]//g'
sed 's/[[]//g'
Compare a remote file with a local file
ssh user@host cat /path/to/remotefile | diff /path/to/localfile -
Credit to User Root
Compare files in a directory
diff -bur folder1/ folder2/
Warning: when doing diff on folders, if the timestamps are different it will think the files are different. If you actually compare the files, they will be the same.
Console Clock in corner
while true; do echo -ne "\e[s\e[0;$((COLUMNS-27))H$(date)\e[u"; sleep 1; done &
Warning, this auto scrolls your SSH session. To kill it, do:
ps aux | grep bash | grep -v grep
Then kill the bash session at the time you ran it:
kill <processid>
Credit to User Squiidux
Create backup of file whilst in vim
vim file :!cp % %-
Press enter and continue to edit
Credit to User MPB
Cronjob/Crontab
crontab -e crontab -l * * * * * command to be executed - - - - - | | | | | | | | | +----- day of week (0 - 6) (Sunday=0) | | | +------- month (1 - 12) | | +--------- day of month (1 - 31) | +----------- hour (0 - 23) +------------- min (0 - 59)
Guides:
http://www.adminschoice.com/crontab-quick-reference
To do a job every X minutes, do */X
To do a job every day at X hour on the hour, do 0 9 * * * for 9am each day.
To do a job every minute in a specific hour, do * X * * *
To monitor active cron jobs, do tail -f /var/log/cron
/usr/local/bin/php: No such file or directory
Do whereis php
Generally it is actually in /usr/bin/php
Cron Daemon email
If you get the below email:
cd / && run-parts --report /etc/cron.daily /etc/cron.daily/sysklogd: chown: cannot access `/var/log/mail.warn': No such file or directory chown: cannot access `/var/log/syslog': No such file or directory chown: cannot access `/var/log/mail.info': No such file or directory
Do the following:
cd /var/log touch /var/log/mail.warn /var/log/syslog /var/log/mail.info /etc/init.d/sysklogd restart
Execute one off command whenever
echo "ls -l" | at midnight
This is an alternative to cron which allows a one-off task to be scheduled for a certain time.
Credit to User Root
File Permissions
One of the best permissions guide
The values and their equivalent permissions. R is Read, W is Write and X is Execute. There are three sets on a file or folder (e.g. -rwx-w--w- , -rw-r--r-- , -rwxr-xrwx) so you need to put in a value of three (or four in rare occasions) for a file/folder e.g. 644.
0 ---<br> 1 --x 2 -w- 3 -wx 4 r-- 5 r-x 6 rw- 7 rwx
The syntax for chmod is (for example) 755 fileorfolder. The -R option can also be used to set the permissions on anything below a folder.
The syntax for chown is chown user:group fileorfolder . To apply the user:group to anything below a folder you need to use the -R option.
Permissions Calculator
Help Guide 1
Help Guide 2
Unix Notation
File protection with chmod
If you use PHP Support as Apache module, it will use the third value of -rw- r-- r-x to permissions. If it is using Fast CGI it will use the user:group for the first two values -rwx rw- --x
If you are using Plesk a good place to check if you are getting Forbidden errors on your website is /var/www/vhosts/yourdomain.com/httpdocs/statistics/logs/error_log . Access your site and tail -f that file. If you get .htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable name your .htaccess file correctly, set your httpdocs to 757 and see this link.
Special permissions
There is also a, g & s which are not widely used as it just needs additional representation at the special/setid permission to the group.
To set a file to -rws--x--x for example use
4 = setuid - s 2 = setgid - s 4 + 2 = S 1 = Sticky Bit 4 + 2 + 1 = T 2511 -r-x--s--x (e.g. /var/qmail/bin/qmail-remote or /var/qmail/bin/qmail-queue) 4655 -rwSr-xr-x 4711 -rws--x--x 4744 -rwsr--r-- 4755 -rwsr-xr-x 6411 -r-S--s--x. 6511 -r-s--s--x 6644 -rwSr-Sr-- 6666 -rwSrwSrw- 7000 ---S--S--T 7644 -rwSr-Sr-T 7711 -rws--s--t 7744 -rwsr-Sr-T 7755 -rwsr-sr-t
Owner and Group advice for websites
File Locations (index priority)
/etc/apache2/mods-enabled/dir.conf (on Ubuntu) or /etc/httpd/conf/httpd.conf (on CentOS, ~line 402) and it should show something like:
DirectoryIndex index.html index.html.var index.shtml index.cfm index.php index.htm
This shows the default priority in which the index page is picked up and this can be set in the .htaccess file as well with:
DirectoryIndex index.html index.php
These are good places to check if you are using all of your disk space.
cd /var/log
cd /var/www/vhosts (website and statistics)
cd /var/lib/mysql (database) or mysql/mysql
cd /usr/bin/mysqldump (mysql dump)
cd var/qmail (mail logs, queue and configuration)
cd /var/lib/psa/dumps (physical Plesk backups)
cd opt/psa/tmp/ (Plesk stores temporary files here for backups)
Find command guide
FreeBSD
- mysqldump location: /mysql/bin/mysqldump
- Remove syntax:
- rm -r folderName
- Generic tunneling interface starts with gif
Check software versions
fetch instead of wget
To download a file.
whereis instead of locate command
To find files/folders.
Full Directory listing
apt-get install tree yum install tree tree > tree.txt
If you feel adventurous do cat tree.txt , it will take a while ;)
Find the deepest directory in your server/file structure
find . -type d -printf '%d:%p\n' | sort -n | tail -1
Find and remove specific file types from current directory
cd into the directory
find . -type f -name '*.filetype' -exec rm -v {} \;
Line count a file
wc -l /file/path
Generate random number
Between 1 and 10:
seq 10| shuf | head -1
GeoIP - Block countries accessing website
Ubuntu: apt-cache search geoip ; apt-get install geoip-database libgeoip-dev libgeoip1 python-geoip geoip-bin libapache2-mod-geoip tclgeoip
CentOS: yum list |grep -i geo , yum install GeoIP.x86_64
http://www.webhostingtalk.com/showthread.php?t=959646
http://askmatt.co.uk/blog/2010/05/block-countries-using-apache-mod-geo-ip-list-of-countries-by-fraud-risk
.htaccess
inode usage
df --si df -ih
A lot of the time the cause can be /tmp (/var/lib/php/session/ on Plesk) due to sessions. You may want to delete the files in there.
LSB Init Scripts
Maldet
Always run your scans from in Screen, and detach by doing CTRL + A, then press D
Scan reports are normally stored in /usr/local/maldetect/sess/ as session. files.
maldet -a -e -l filepath
Manually alter time/date
Ubuntu
date date mmddtimeyear #as seen below
Cent OS
cd /etc/
ls -lah
rm localtime
ln -s /usr/share/zoneinfo/Europe/London /etc/localtime
date mmddtimeyear
| | | | ---> 2012
| | | 24hr --> XX:XX without :
| | dd -------> day
| mm ---------> month
/etc/init.d/ntpd restart or start
date
PID
Under construction.
Process ID.
To determine the usage of a specific process, do top -p PID
The maximum number of pids can be obtained from /proc/sys/kernel/pid_max
Restart service or service
Useful for differently named ones, e.g.
[ -f /etc/init.d/mysqld ] && service mysqld restart ; [ -f /etc/init.d/mysql ] && service mysql restart
[ -f /etc/init.d/httpd ] && service httpd restart ; [ -f /etc/init.d/apache2 ] && service apache2 restart
Rough Hostname guide
If the server runs Plesk and Virtuozzo, the permanent one needs setting on the hardware or in Virtuozzo.
Run dig -x IP.IP.IP.IP from any Linux server and it will show you the PTR/hostname.
Note: Most servers by default come with a non resolving hostname of localhost, localhost.localdomain or something generic.
The hostname should never be left as the default value on a server sending mail, as it is one of three things mail recipient's mailservers see to determine if mail is spam or not. The other two are reverse DNS and the SMTP banner.
If Plesk throws an error when clicking Websites & Domains tab regarding hostname -f, see this resolution.
Roughly list file count
This includes nested directories:
find /full/file/path -type f | wc -l
SCP Command - Secure Copy
To secure copy a file from one Linux server to another, use the following syntax form:
scp -P PORT file user@IPAddress:/filepath
For example:
scp -P 22 index.html [email protected]:/
To move a folder, put -r in between the port and the folder. If you receive the following error while trying to SCP a file from one server to the other:
stdin: is not a tty
You can solve the issue quickly by doing the following on the destination server:
vi ~/.bashrc if [ $(expr index "$-" i) -eq 0 ]; then return fi
Screen
Manage Multiple sessions in one Terminal
Tips and Tricks
Setting the time
http://geoffhankerson.com/node/112
http://codeghar.wordpress.com/2007/12/06/manage-time-in-ubuntu-through-command-line/
System Logs and Shutdown troubleshooting
If you are having an issue, a reboot should not be performed if the server can be accessed in any way (e.g. locally in the data centre, only if it is a Dedicated server). This is because after a reboot there is little you can find out from the logs as the important logs get cleared on restart.
last reboot last /var/log/syslog /var/log/kern.log /var/log/dmesg /var/log/messages grep -i error /var/log/messages ; grep -i panic /var/log/messages ; grep -i warning /var/log/messages errpt
To find .log files, run updatedb and then locate *.log
To restart and on boot do a disk check do (or -rF):
shutdown -Fr now
tar command
To archive and compress a folder/files do:
tar -czvf files.tgz files/ tar -czvf folder.tar.gz folder/ tar cvf mubackup.tar mu/ ; gzip -9 mubackup.tar #.tgz is same as .tar.gz
c creates the archive (tar), z compresses it into the gzip, v is verbose, f is the file/folder
To extract do:
#for tar tar xvf file.tar #for .tgz or tar.gz tar xvfz file.tar.gz
User is not in the sudoers file
If you try to sudo into a server or run sudo and get the following message:
"is not in the sudoers file. This incident will be reported."
Do the following command as root and add the username into the file in the same format as the root user:
visudo
Use unusual characters in filenames
If you want to specify a space, you need to name the file/folder as follows:
File = /usr/local/etc/testingdatabase.sql
mv /usr/local/etc/testingdatabase.sql /usr/local/etc/testing\ database.sql
This will make the file be testing database.sql , on command line this will appear as testing\ database.sql .
A backslash symbol \ needs to be used before an apostrophe ' , bracket (), exclamation/bang ! symbol or question marks ?:
01\ -\ It\'s\ You.txt #How it appears: 01 - It's You.txt 02\ -\ Boom\!.m3u #How it appears: 02 - Boom!.m3u 03\ -\ Why\ Wont\ You\ Work\?.sh #How it appears: 03 - Why Wont You Work?.sh 04\ -\ Musical\ Playlist\ For\ \(VPS\)\ Server.m3u #How it appears: 04 - Musical Playlist For (VPS) Server.m3u
updatedb (locate command)
This command is used when you cannot locate a file and you get "locate: warning: database /var/lib/slocate/slocate.db' is more than 8 days old". It is advised to run updatedb at least once a month. However if you get the following error when using it:
updatedb: fatal error: load_file: Could not open file: /etc/updatedb.conf: No such file or directory
You need to create or edit this file
vim /etc/updatedb.conf
and put the following inside of it:
PRUNE_BIND_MOUNTS="yes"PRUNEPATHS="/tmp /var/spool /media"PRUNEFS="NFS nfs nfs4 rpc_pipefs afs binfmt_misc proc smbfs autofs iso9660 ncpfs coda devpts ftpfs devfs mfs shfs sysfs cifs lustre_lite tmpfs usbfs udf"
Alternatively run the below script after reading this file http://serverkb.co.uk/tools/README.txt:
http://serverkb.co.uk/tools/updatedbscript.sh
VPS Hints and Tips
To check for the filepath of a command run top and then press c.
If it is a container on a node, there are generally no datacentre / rack level restrictions as the container is virtualised on a node. The only restrictions are what is put in place via the container itself effectively.
To list all open Internet, x.25 (HP-UX), and UNIX domain files, use:
lsof -i -U
WHOIS script
apt-get install pv ; cd /var/www/vhosts ; ls -l | awk ' {print $9}' > domainlist ; wget serverkb.co.uk/tools/findregistrar.sh ; chmod +x findregistrar.sh
For CentOS use yum -y install jwhois.x86_64
Edit the file and replace domain registrar with the one you want to find. Then do:
./findregistrar.sh
write error
If you get the following error when doing write user TTYsession or write user Session:
write: write: you have write permission turned off.
Do this to fix the problem:
mesg y
