Essential Unix/Linux Commands Every User Should Master

1. tar

Create, list, and extract tar archives.

$ tar cvf archive_name.tar dirname/

$ tar xvf archive_name.tar

$ tar tvf archive_name.tar

2. grep

Search for patterns in files.

$ grep -i "the" demo_file

$ grep -A 3 -i "example" demo_text

$ grep -r "ramesh" *

3. find

Locate files by name and execute actions.

$ find -iname "MyProgram.c"

$ find -iname "MyProgram.c" -exec md5sum {} \;

$ find ~ -empty

4. ssh

Connect to remote hosts and debug the client.

$ ssh -l jsmith remotehost.example.com

$ ssh -v -l jsmith remotehost.example.com

$ ssh -V

5. sed

Stream editor for text transformations.

$ sed 's/.$//' filename

$ sed -n '1!G; h; p' filename

$ sed '/./=' thegeekstuff.txt | sed 'N; s/
/ /'

6. awk

Pattern‑scanning and processing language.

$ awk '!($0 in array) { array[$0]; print}' temp

$ awk -F ':' '$3=$4' /etc/passwd

$ awk '{print $2,$5;}' employee.txt

7. vim

Open files at specific lines or patterns.

$ vim +10 filename.txt

$ vim +/search-term filename.txt

$ vim -R /etc/passwd

8. diff

Compare files while ignoring whitespace.

$ diff -w name_list.txt name_list_new.txt

9. sort

Sort file contents in various ways.

$ sort names.txt

$ sort -r names.txt

$ sort -t: -k 3n /etc/passwd | more

10. export

Set or display environment variables.

$ export | grep ORACLE

$ export ORACLE_HOME=/u01/app/oracle/product/10.2.0

11. xargs

Build and execute command lines from standard input.

$ ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory

$ find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz

$ cat url-list.txt | xargs wget -c

12. ls

List directory contents with human‑readable sizes, timestamps, or file types.

$ ls -lh

$ ls -ltr

$ ls -F

13. pwd

Print the current working directory.

$ pwd

14. cd

Change directories; cd - toggles between the last two locations. Enable spelling correction with shopt -s cdspell.

$ cd -

15. gzip

Compress and decompress .gz files.

$ gzip test.txt

$ gzip -d test.txt.gz

$ gzip -l *.gz

16. bzip2

Compress and decompress .bz2 files.

$ bzip2 test.txt

$ bzip2 -d test.txt.bz2

17. unzip

Extract .zip archives and list their contents.

$ unzip test.zip

$ unzip -l jasper.zip

18. shutdown

Power off or reboot the system.

$ shutdown -h now

$ shutdown -h +10

$ shutdown -r now

$ shutdown -Fr now

19. ftp

Transfer files via FTP.

$ ftp IP/hostname

ftp> mget *.html

20. crontab

View and schedule recurring tasks.

$ crontab -u john -l

*/10 * * * * /home/ramesh/check-disk-space

21. service

Manage System V init scripts.

$ service ssh status

$ service --status-all

$ service ssh restart

22. ps

Display running processes.

$ ps -ef | more

$ ps -efH | more

23. free

Show memory usage; options change units.

$ free

$ free -g

$ free -t

24. top

Interactive process viewer; change sort field with O and filter by user.

$ top -u oracle

25. df

Report filesystem disk usage; -h for human‑readable, -T to show type.

$ df -k

$ df -h

$ df -T

26. kill

Terminate processes by PID; alternatives include killall, pkill, xkill.

$ ps -ef | grep vim

$ kill -9 7243

27. rm

Remove files or directories with safety prompts.

$ rm -i filename.txt

$ rm -i file*

$ rm -r example

28. cp

Copy files while preserving attributes.

$ cp -p file1 file2

$ cp -i file1 file2

29. mv

Rename or move files; -i prompts, -v shows progress.

$ mv -i file1 file2

$ mv -v file1 file2

30. cat

Concatenate and display file contents; -n adds line numbers.

$ cat file1 file2

$ cat -n /etc/logrotate.conf

31. mount

Mount filesystems manually or via /etc/fstab.

# mkdir /u01 && mount /dev/sdb1 /u01

/dev/sdb1 /u01 ext2 defaults 0 2

32. chmod

Change file permissions.

$ chmod ug+rwx file.txt

$ chmod g-rwx file.txt

$ chmod -R ug+rwx file.txt

33. chown

Change file owner and group.

$ chown oracle:dba dbora.sh

$ chown -R oracle:dba /home/oracle

34. passwd

Modify user passwords; root can change others without prompting.

$ passwd

# passwd USERNAME

# passwd -d USERNAME

35. mkdir

Create directories; -p creates parent paths as needed.

$ mkdir ~/temp

$ mkdir -p dir1/dir2/dir3/dir4/

36. ifconfig

Display and configure network interfaces.

$ ifconfig -a

$ ifconfig eth0 up

$ ifconfig eth0 down

37. uname

Show system information such as kernel version.

$ uname -a

38. whereis

Locate binaries, sources, and manuals.

$ whereis ls

$ whereis -u -B /tmp -f lsmk

39. whatis

Display a brief description of a command.

$ whatis ls

$ whatis ifconfig

40. locate

Find files by name using a prebuilt database.

$ locate crontab

41. man

Read manual pages; sections categorize command types.

$ man crontab

$ man 5 crontab

42. tail

Show the end of files; -n sets line count, -f follows updates.

$ tail filename.txt

$ tail -n 20 filename.txt

$ tail -f log-file

43. less

Page through large files without loading them entirely. $ less huge-log-file.log Use CTRL+F to move forward and CTRL+B to move backward.

44. su

Switch user identity; root can become any user without a password.

$ su - USERNAME

$ su - raj -c 'ls'

$ su -s 'SHELLNAME' USERNAME

45. mysql

Interact with MySQL databases locally or remotely.

$ mysql -u root -p -h 192.168.1.2

$ mysql -u root -p

46. yum

Package manager for RPM‑based distributions.

$ yum install httpd

$ yum update httpd

$ yum remove httpd

47. rpm

Low‑level RPM package handling.

# rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm

# rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm

# rpm -ev httpd

48. ping

Test network connectivity; limit packet count with -c.

$ ping -c 5 gmail.com

49. date

Set system date and synchronize hardware clock.

# date -s "01/31/2010 23:59:53"

# hwclock --systohc --utc

50. wget

Download files from the web.

$ wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz