Linux Command Examples
19. ftp command examples
Both ftp and secure ftp (sftp) has similar commands. To connect to a remote server and download multiple files, do the following. $ ftp IP/hostname ftp> mget *.html To view the file names located on the remote server before downloading, mls ftp command as shown below. ftp> mls *.html - /ftptest/features.html /ftptest/index.html /ftptest/othertools.html /ftptest/samplereport.html /ftptest/usage.html
34. 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
11. 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
28. 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
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
12. ls command examples
Display filesize in human readable format (e.g. KB, MB etc.,) $ ls -lh -rw-r----- 1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz 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
41. man command examples
Display the man page of a specific command. $ man crontab When a man page for a command is located under more than one section, you can view the man page for that command from a specific section as shown below. $ man SECTION-NUMBER commandname Following 8 sections are available in the man page: General commands, System calls, C library functions, Special files (usually devices, those found in /dev) and drivers, File formats and conventions, Games and screensavers, also Miscellaneous System administration commands and daemons For example, when you do whatis crontab, you'll notice that crontab has two man pages (section 1 and section 5). To view section 5 of crontab man page, do the following: $ man 5 crontab
25. df command examples
Displays the file system disk space usage. By default df -k displays output in bytes. df -h displays output in human readable form. i.e size will be displayed in GB's. Use -T option to display what type of file system.
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
35. 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/
27. 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
7. vim command examples
Go to the 143rd line of file $ vim +143 filename.txt Go to the first match of the specified $ vim +/search-term filename.txt Open the file in read only mode. $ vim -R /etc/passwd
8. diff command examples
Ignore white space while comparing. # diff -w name_list.txt name_list_new.txt example: 2c2,3 < John Doe --- > John M Doe > Jason Bourne
4. ssh command examples
Login to remote host ssh -l jsmith remotehost.example.com Debug ssh client ssh -v -l jsmith remotehost.example.com Display ssh client version $ ssh -V
48. ping command examples
Ping a remote host by sending only 5 packets. $ ping -c 5 gmail.com
42. 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
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
29. 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
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" *
21. service command examples
Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the /etc/init.d/ directory with their full path, you can use the service command. Check the status of a service: # service ssh status Check the status of all the services. service --status-all Restart a service. # service ssh restart
49. 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
18. 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
9. 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
44. 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 Execute a single command from a different account name. In the following example, john can execute the ls command as raj username. Once the command is executed, it will come back to john's account. [john@dev-server]$ su - raj -c 'ls' [john@dev-server]$ Login to a specified user account, and execute the specified shell instead of the default shell. $ su -s 'SHELLNAME' USERNAME
50. 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/scripts/download_script.php?src_id=7701
23. 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. 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.If you want to see a total memory ( including the swap), use the -t switch, which will display a total line.
16. bzip2 command examples
To create a *.bz2 compressed file: $ bzip2 test.txt To uncompress a *.bz2 file: bzip2 -d test.txt.bz2
15. 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 compressed uncompressed ratio uncompressed_name 23709 97975 75.8% asp-patch-rpms.txt
17. 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 Archive: jasper.zip Length Date Time Name -------- ---- ---- ---- 40995 11-30-98 23:50 META-INF/MANIFEST.MF 32169 08-25-98 21:07 classes_ 15964 08-25-98 21:07 classes_names 10542 08-25-98 21:07 classes_ncomp
47. 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
46. yum command examples
To install apache using yum. $ yum install httpd To upgrade apache using yum. $ yum update httpd To uninstall/remove apache using yum. $ yum remove httpd
31. 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
10. export command examples
To view oracle related environment variables. $ export | grep ORACLE declare -x ORACLE_BASE="/u01/app/oracle" declare -x ORACLE_HOME="/u01/app/oracle/product/10.2.0" declare -x ORACLE_SID="med" declare -x ORACLE_TERM="xterm" To export an environment variable: $ export ORACLE_HOME=/u01/app/oracle/product/10.2.0
37. 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 "Linux john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686 GNU/Linux"
14. cd command examples
Use "cd -" to toggle between the last two directories. Use "shopt -s cdspell" to automatically correct mistyped directory names on cd.
36. 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
26. 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
40. 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. For example locate command shows all files in the system that contains the word crontab in it. (locate crontab)
20. crontab command examples
View crontab entry for a specific user # crontab -u john -l Schedule a cron job every 10 minutes. */10 * * * * /home/ramesh/check-disk-space
39. whatis command examples
Whatis command displays a single line description about a command. $ whatis ls (ls (1) - list directory contents) $ whatis ifconfig (ifconfig (8) - configure a network interface)
5. sed command examples
When you copy a DOS file to Unix, you could find \r\n in the end of each line. This example converts the DOS file format to Unix file format using sed command. $sed 's/.$//' filename Print file content in reverse order $ sed -n '1!G;h;$p' thegeekstuff.txt Add line number for all non-empty-lines in a file $ sed '/./=' thegeekstuff.txt | sed 'N; s/\n/ /'
38. whereis command examples
When you want to find out where a specific Unix command exists (for example, where does ls command exists?), you can execute the following command. $ whereis ls ls: /bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz When you want to search an executable from a path other than the whereis default path, you can use -B option and give path as argument to it. This searches for the executable lsmk in the /tmp directory, and displays it, if it is available. $ whereis -u -B /tmp -f lsmk lsmk: /tmp/lsmk
30. 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 1 /var/log/btmp { 2 missingok 3 monthly 4 create 0660 root utmp 5 rotate 1 6 }
32. 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
33. 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
43. 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
45. mysql command examples
mysql is probably the most widely used open source database on Linux. Even if you don't run a mysql database on your server, you might end-up using the mysql command ( client ) to connect to a mysql database running on the remote server. To connect to a remote mysql database. This will prompt for a password. $ mysql -u root -p -h 192.168.1.2 To connect to a local mysql database. $ mysql -u root -p If you want to specify the mysql root password in the command line itself, enter it immediately after -p (without any space).
22. 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
13. 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.
24. 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. Current Sort Field: P for window 1:Def Select sort field via field letter, type any other key to return a: PID=Process Id v: nDRT=Dirty Pages count d: UID=User Id y: WCHAN=Sleeping in Function e: USER= User Name z: Flags=Task Flags ........ To displays only the processes that belong to a particular user use -u option. The following will show only the top processes that belongs to oracle user. $ top -u oracle
