1. tar command examples
Create a new tar archive.$ tar cvf archive_name.tar dirname/
Extract from an existing tar archive.
$ tar xvf archive_name.tar
View an existing tar archive.
$ tar tvf archive_name.tar
2. grep command examples
Search for a given string in a file (case in-sensitive search).$ grep -i "the" demo_file
Print the matched line, along with the 3 lines after it.
$ grep -A 3 -i "example" demo_text
Search for a given string in all files recursively
$ grep -r "ramesh" *
3. find command examples
Find files using file-name ( case in-sensitve find)$ find -iname "MyCProgram.c"
Execute commands on files found by the find command
$ find -iname "MyCProgram.c" -exec md5sum {} \;
Find all empty files in home directory
$ find ~ -empty
4. awk command examples
Remove duplicate lines using awk$ awk '!($0 in array) { array[$0]; print }' temp
Print all lines from /etc/passwd that has the same uid and gid
$awk -F ':' '$3==$4' passwd.txt
Print only specific field from a file.
$ awk '{print $2,$5;}' employee.txt
5. sort command examples
Sort a file in ascending order$ sort names.txt
Sort a file in descending order
$ sort -r names.txt
Sort passwd file by 3rd field.
$ sort -t: -k 3n /etc/passwd | more
6. xargs command examples
Copy all images to external hard-drive# ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory
Search all jpg images in the system and archive it.
# find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz
Download all the URLs mentioned in the url-list.txt file
# cat url-list.txt | xargs wget –c
7. ls command examples
Display filesize in human readable format (e.g. KB, MB etc.,)$ ls -lh
Order Files Based on Last Modified Time (In Reverse Order) Using ls -ltr
$ ls -ltr
Visual Classification of Files With Special Characters Using ls -F
$ ls -F
8. pwd command
pwd is Print working directory. What else can be said about the good old pwd who has been printing the current directory name for ages.9. cd command examples
Use “cd -” to toggle between the last two directories10. gzip command examples
To create a *.gz compressed file:$ gzip test.txt
To uncompress a *.gz file:
$ gzip -d test.txt.gz
Display compression ratio of the compressed file using gzip -l
$ gzip -l *.gz
11. bzip2 command examples
To create a *.bz2 compressed file:$ bzip2 test.txt
To uncompress a *.bz2 file:
$bzip2 -d test.txt.bz2
12. unzip command examples
To extract a *.zip compressed file:$ unzip test.zip
View the contents of *.zip file (Without unzipping it):
$ unzip -l jasper.zip
13. shutdown command examples
Shutdown the system and turn the power off immediately.# shutdown -h now
Shutdown the system after 10 minutes.
# shutdown -h +10
Reboot the system using shutdown command.
# shutdown -r now
Force the filesystem check during reboot.
# shutdown -Fr now
Shutdown System after 10:00 pm
#s shutdown 22:00
14. ps command examples
ps command is used to display information about the processes that are running in the system.While there are lot of arguments that could be passed to a ps command, following are some of the common ones.
To view current running processes.
$ ps -ef | more
To view current running processes in a tree structure. H option stands for process hierarchy.
$ ps -efH | more
15. free command examples
This command is used to display the free, used, swap memory available in the system.Typical free command output. The output is displayed in bytes.
$ free
If you want to quickly check how many GB of RAM your system has use the -g option. -b option displays in bytes, -k in kilo bytes, -m in mega bytes.
$ free -g
16. top command examples
top command displays the top processes in the system ( by default sorted by cpu usage ). To sort top output by any column, Press O (upper-case O) , which will display all the possible columns that you can sort by as shown below.17. df command examples
Displays the file system disk space usage. By default df -k displays output in bytes.$ df -k
df -h displays output in human readable form. i.e size will be displayed in GB’s.
18. kill command examples
Use kill command to terminate a process. First get the process id using ps -ef command, then use kill -9 to kill the running Linux process as shown below. You can also use killall, pkill, xkill to terminate a unix process.$ ps -ef | grep vim
ramesh 7243 7222 9 22:43 pts/2 00:00:00 vim
$ kill -9 7243
19. rm command examples
Get confirmation before removing the file.$ rm -i filename.txt
It is very useful while giving shell metacharacters in the file name argument.
Print the filename and get confirmation before removing the file.
$ rm -i file*
Following example recursively removes all files and directories under the example directory. This also removes the example directory itself.
$ rm -r example
20. cp command examples
Copy file1 to file2 preserving the mode, ownership and timestamp.$ cp -p file1 file2
Copy file1 to file2. if file2 exists prompt for confirmation before overwritting it.
$ cp -i file1 file2
21. mv command examples
Rename file1 to file2. if file2 exists prompt for confirmation before overwritting it.$ mv -i file1 file2
Note: mv -f is just the opposite, which will overwrite file2 without prompting.
mv -v will print what is happening during file rename, which is useful while specifying shell metacharacters in the file name argument.
$ mv -v file1 file2
22. cat command examples
You can view multiple files at the same time. Following example prints the content of file1 followed by file2 to stdout.$ cat file1 file2
While displaying the file, following cat -n command will prepend the line number to each line of the output.
$ cat -n /etc/logrotate.conf
23. mount command examples
To mount a file system, you should first create a directory and mount it as shown below.# mkdir /u01
# mount /dev/sdb1 /u01
You can also add this to the fstab for automatic mounting. i.e Anytime system is restarted, the filesystem will be mounted.
/dev/sdb1 /u01 ext2 defaults 0 2
24. chmod command examples
chmod command is used to change the permissions for a file or directory.Give full access to user and group (i.e read, write and execute ) on a specific file.
$ chmod ug+rwx file.txt
Revoke all access for the group (i.e read, write and execute ) on a specific file.
$ chmod g-rwx file.txt
Apply the file permissions recursively to all the files in the sub-directories.
$ chmod -R ug+rwx file.txt
25. chown command examples
chown command is used to change the owner and group of a file. \To change owner to oracle and group to db on a file. i.e Change both owner and group at the same time.
$ chown oracle:dba dbora.sh
Use -R to change the ownership recursively.
$ chown -R oracle:dba /home/oracle
26. passwd command examples
Change your password from command line using passwd. This will prompt for the old password followed by the new password.$ passwd
Super user can use passwd command to reset others password. This will not prompt for current password of the user.
# passwd USERNAME
Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.
# passwd -d USERNAME
27. mkdir command examples
Following example creates a directory called temp under your home directory.$ mkdir ~/temp
Create nested directories using one mkdir command. If any of these directories exist already, it will not display any error. If any of these directories doesn’t exist, it will create them.
$ mkdir -p dir1/dir2/dir3/dir4/
28. ifconfig command examples
Use ifconfig command to view or configure a network interface on the Linux system.View all the interfaces along with status.
$ ifconfig -a
Start or stop a specific interface using up and down command as shown below.
$ ifconfig eth0 up
$ ifconfig eth0 down
29. uname command examples
Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number,Processor type, etc.,
Sample uname output from a Ubuntu laptop is shown below.
$ uname -a
30. locate command examples
Using locate command you can quickly search for the location of a specific file (or group of files). Locate command uses the database created by updatedb.The example below shows all files in the system that contains the word crontab in it.
$ locate crontab
31. tail command examples
Print the last 10 lines of a file by default.$ tail filename.txt
Print N number of lines from the file named filename.txt
$ tail -n N filename.txt
View the content of the file in real time using tail -f. This is useful to view the log files, that keeps growing. The command can be terminated using CTRL-C.
$ tail -f log-file
32. less command examples
less is very efficient while viewing huge log files, as it doesn’t need to load the full file while opening.$ less huge-log-file.log
One you open a file using less command, following two keys are very helpful.
CTRL+F – forward one window
CTRL+B – backward one window
34. su command examples
Switch to a different user account using su command. Super user can switch to any other user without entering their password.$ su - USERNAME
35. rpm command examples
To install apache using rpm.# rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm
To upgrade apache using rpm.
# rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm
To uninstall/remove apache using rpm.
# rpm -ev httpd
36. ping command examples
Ping a remote host by sending only 5 packets.$ ping -c 5 gmail.com
37. date command examples
Set the system date:# date -s "01/31/2010 23:59:53"
Once you’ve changed the system date, you should syncronize the hardware clock with the system date as shown below.
# hwclock –systohc
# hwclock --systohc –utc
38. wget command examples
The quick and effective method to download software, music, video from internet is using wget command.$ wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz
Download and store it with a different name.
$ wget -O taglist.zip http://www.vim.org/script/download_script.php?src_id=7701
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