- To find hardware details of linux box: dmesg |less
- To find linux version: cat /proc/version
- To find cpu info: cat /proc/cpuinfo
- To unzip gzip file: gunzip something.tar.gz
- To untar tar file: tar xvf something.tar
- To unzip and untar in one step: tar xvzf something.tar.gz
- To install a software from rpm: rpm -iv myapp_someversion.rpm
- To edit your bash shell environment edit ~/.bashrc file
- To set the java and ant class path add the following lines in your bashrc file at home directory with appropriate java and ant directories:
export JAVA_HOME=/usr/java/jdk1.5.0_09
export ANT_HOME=/home/oracle/apache-ant-1.7.0
export PATH=$PATH:${JAVA_HOME}/bin:${ANT_HOME}/bin
export CLASSPATH=./:${JAVA_HOME}/lib/tools.jar:${JAVA_HOME}/lib/rt.jar:${ANT_HOME}/lib/ant.jar
- To list all the background running oracle process in the system: ps -ef|grep "ora_"|grep -v grep
- To give a short name to big command: alias listoraprocess="ps -ef|grep "ora_"|grep -v grep"
- To kill all oracle process: ps -ef|grep "ora_"|grep -v grep|grep $ORACLE_SID|awk '{print $2}'|xargs kill -9
- To list all files in current directory: find . -print
- To search for string "error" in all files in current directory: find . -print|xargs grep -i error
- To print time of execution for the bash script:
#!/usr/bin/env bash
curtime=`date +"%s"`
#Your bash script statements here
echo "Time of execution is `expr $(date +'%s') - $curtime` seconds"
- To reboot linux in 10 minutes with broadcast message: shutdown -h +10 "scheduled maintenance"
- To find number of logged users: who | wc -l
- To check the type of a command: type cd , type who
- To echo System variables: echo $DISPLAY $HOME $MAIL $OLDPWD $PATH $PWD $SHELL $TERM $USER
- To print shell's environment variables: env or printenv
- To set command line editing using vi: set -o vi
- To execute the last command which was executed begining with p: !p
- To execute a command as background job use &: ls -al &
- To list all pending jobs: jobs
- To create softlink (shortcut, deleting shoftlink doesn't delete original file): ln -s myfile softlink
- To create hardlink (deleting hardlink deletes original file):ln -s myfile softlink
- To find where the link is pointing to: ls -l linkname
- To simply view files use one of these commands:
- cat - View files in their entirety
- more - View files one page at a time
- less - View files one page at a time. Ability to move backwards by pressing b.
- head - View the first lines of a file
- tail - View the last lines of a file
- nl - View files with their lines numbered
- To continuously tail a log file: tail -f mylog.log
- To update timestamp of a file ot create a empty file: touch filename
- To change the default editor set the following environment variables
$EDITOR=emacs
$VISUAL=emacs
$export EDITOR VISUAL
- To count number of byte words and lines in a file: wc filename
- To count only number of lines in a file: wc -l filename
- To list important attributes of a file like size device access : stat filename
- To print size of files: du file1 file2
- To print all filenames begining with myfile: find / -type f -name myfile* -print
- To print all directories begining from current: find . -type d -print
- To print lines containg myword in a file myfile: grep myword myfile
- To print lines which doesn't contain myword in myfile: grep -v myword myfile
- To display only unique lines in sorted order from a file: sort myfile | uniq
- To count duplicate lines: sort myfile | uniq -c
- To display command out and also write into a file simultaneously use tee command:
who | tee who_output | sort
- To print 2nd and 4th word in each line in myfile: awk '{print $2, $4}' myfile
- To print all lines shorter than 50 characters in myfile: awk '{length($0) < 50}' myfile
- To print contents of myfile with all occurance or red converted to blue: sed 's/red/blue/g' myfile
- To print contents of myfile skipping lines 2 to 5: sed '2,3d' myfile
- To substitute all occurance of NAME with Kris and AGE with 31 in myfile:
m4 -DNAME=Kris -DAGE=31 myfile
- To find size, used space, and free space on all disk partition: df -h
- To find size, used space, and free space current directory: df .
- To compare two directories recursively: diff -r dir1 dir2
- To compare two file ignoring case: diff -i file1 file2
- To compare tabular sorted file skipping 2nd column : comm -2 file1 file2
- To point out the first diffrence in similar files: cmp file1 file2
- To print 32 byte checksum, useful to check downloaded files: md5sum file1
- To print name of the terminal device associated with the current shell: tty
- To format output display string: printf "User %s is %d years old.\n" kris 31
- To enter "y" to a interactive shell program by default: yes | my_interactive_command
- To print current year business calendar with day number: cal -y -m
- To print current year business calendar with sequential numbers instead of date: cat -y -m -j
- To print epoch seconds: date - %s
- To print last modified timestamp of a file: date -r myfile
- To print Hello every 10 seconds: sleep 10 && echo 'Hello'
- To check which files are newly added to current directory ever 20 seconds: watch -n 20 ls -l
- To view your own process: ps -ux
- To view process started by user1: ps -U user1
- To view all occurance of a program name prg: ps -C prg
- To view all process in screen width with full command line: ps -efww
- To view all process in screen width with threads: ps -efH
- To find how long the system is running since last boot: uptime
- To display current process of all logged users: w
- To monitor most active processes with full command line: top -c [press q to exit from top]
- To graphical display of system load (similar to task manager in windows) : xload
- To display memory usage in megabyte: free -mt [free -t for kilobytes]
- To run system intensive process with controlled priority 7: nice -7 jobname jobargs > outfile [10 is default]
- To change the priority of a process id 1834 previously executed with nice: nice -5 -p 1834
- To change the priority of a process previously executed by user usr1 with nice: nice -5 -u usr1
- To change the priority of already running command by process id from PS: renice +15 23456
- To find details about user environment like login id, last login etc:
logname : current login name
whoami : same as logname except if su is used to switch user
finger : user information
last : last login details
printenv : environment details
- To find details about your computer: uname -a
- To print your host name: hostname
- To print details of computer's default network interfaces: ifconfig
- To display details of computer's all network interfaces: ifconfig -a
- To display details of a hostname from internet directory: whois hotmail.com
- To print network path from your machine to a host: traceroute yahoo.com
- To scp myfile from current machine to othermachine using id otherid:
scp myfile otherid@remote.example.com:/home/otherhome/
- To scp otherfile from other machine with id other id to current machine:
- To download a file from internet: wget http://www.yahoo.com/index.htm
- To display useful prompt for oracle box:
Put the following in .profile or .bashrc file
PS1="`hostname`*\${ORACLE_SID}-\${PWD}
- To display memory segments: ipcs
- To display all cpu status: mpstat -P ALL
- To display cpu utilization every 5 seconds, 5 times: sar -u 5 5
- To run sar command non interactively to check later: nohup sar -o output.file 12 8 >/dev/null 2>&1 &
- To display highest CPU utilizing process and user: ps -eo pcpu,pid,user,args | sort -k 1 -r | head -5
- To display i/o status every 5 seconds 5 times: iostat -xtc 5 5
- To display virtual memory status every 5 seconds: vmstat 5
- To find files larger than 10KB: find . -size +10240 �print
- To echo quotes: echo 'Single quotes "protect" double quotes' or echo "Well, isn't that \"special\"?"
- To display command output in echo: echo "You have `ls | wc -l` files in `pwd`"
- To display variable value in echo: echo "The value of \$x is $x"
- To sort page and print a file: sort file | pr -3 | lp
- To redirect standard output to standard error: echo "Usage error: see administrator" 1>&2
- To send command output to one file and error to another file: find / -print > fileOne 2>fileTwo
- To remember a directory and use it later:
- pushd /var/dirme
----execute other commands even change directory
- popd
- To create a patch file by using diff between files: diff fileOld fileNew > patchfile
- To apply patch to a file: patch fileOld patchfile
- To create a patch file between directories: diff -Naur prestinedir modifieddir > patchfile
- To apply patch to a directory:
- cd prestinedir
- patch -p1 < patchfile
- To put the most recent command suspended using Ctrl+z in background: bg
- To put a command in background using process number: bg %3
- To find background job number: jobs
- To bring a background process to foreground: fg %4
- To prevent a process being killed when you exit the shell:
- nohup lpr -Phod /var/access.log & (command output goes to nohup.out)
- To split a file based on lines:
- split -l 100 long.txt piece
- more piece*
- To split a file based on size in KB or MB:
- split -b 10k long piece
- split -b 10m long piece
- To add user smith : useradd -d /home/smith -s /bin/bash -g users smith
- To delete user smith: userdel smith
- To change user home directory: usermod -d /u01/smith smith
- To change smith password: passwd smith
- To find user details: finger smith
- To change name and other finger details of smith: chfn smith
- To change shell for smith: chsh smith
- To find all the available shells in the system: chsh -l
- To switch to super user with directory change to /root: su -l or su -
- To switch to super user with current shell and current directory: su
- To print group information of smith: groups smith
- To add new group: groupadd -f newgroup
- To delete group: groupdel group1
- To change group name: groupmod -n newgroupname oldgroupname
- To set hostname: hostname me.myhost.com
- To display current time, number of users logged, how long the system is running and the amount of load into the system: uptime
- To reset terminal when backspace and delete keys produce junk:
- stty erase Delete
- stty intr Ctrl+c
- To change the group file belongs to: chgrp admingroup imp.tar
- To log into new group you belong. This will set the group to new group
without running chgrp:
- newgrp admingrp
Vi editor tips:
- To delete all occurance of DEBUG. ESC :%s/* DEBUG //g
- To delete all occurance of "DEBUG ". ESC :%s/* DEBUG //g
- To delete everything between <> including <> in line numbers 1 to 8. ESC :1,8s/<[^>]*>//g
- To substitute all occurences of foo on the current line with bar. ESC :.s/foo/bar/g
- To subsitute all matches of the word foo in the file with bar. Ignore case in searches.
ESC :%s/foo/bar/g
- To subsitute all matches of the microsoft with the linux. ESC :%s;microsoft/;linux;g
- To edit files found by grep: vi `grep -l ifdef *.java`
- To edit previous command using vi: fc -e vi