Top 25 Linux/UNIX Commands That Every Linux User Should Know

Linux and UNIX based operating system are very powerful. Although Linux interface is user friendly and easy to understand but there are lots of commands that every Linux user should know it. There are lots of thing you can do with the help of commands but can not using GUI.

In this tutorial I will provide a list of Linux commands that every Linux should know it will be also helpful for any beginner to know. Below commands should work on CentOS, Red Hat, Ubuntu, Linux Mint or any other Linux Operating System.

Suggested Read: Top 25 Linux Find Command Examples

1. To Show Time and Date

# date
Tue Feb 7 18:37:39 MSK 2017

2. Checking System Uptime

Check how long system has been running and up?

# uptime
18:39:33 up 583 days, 5:45, 0 users, load average: 0.07, 0.02, 0.00

3. To Know Who Are Logged In As

# whoami
root

4. Check History Of Successful Logged In User

# last
reboot system boot 2.6.32-042stab08 Sun Jul 5 13:54 - 07:24 (583+18:29)
reboot system boot 2.6.32-042stab08 Fri Mar 7 03:21 - 13:53 (485+09:31)
reboot system boot 2.6.32-042stab05 Mon Sep 17 22:37 - 13:53 (1020+15:15)
reboot system boot 2.6.32-042stab05 Mon Sep 17 20:07 - 22:36 (02:28)
reboot system boot 2.6.32-042stab05 Tue Apr 24 20:06 - 20:07 (146+00:00)
reboot system boot 2.6.32-042stab05 Thu Apr 12 22:14 - 20:07 (157+21:52)
reboot system boot 2.6.18-194.8.1.e Mon Apr 2 10:06 - 22:13 (10+12:06)
reboot system boot 2.6.32-042stab03 Tue Feb 21 10:41 - 03:30 (40+15:49)
wizap pts/1 c-68-51-136-80.h Sun Nov 20 11:16 - 12:00 (00:43)
reboot system boot 2.6.32-042stab03 Mon Nov 7 06:52 - 03:30 (146+19:38)

wtmp begins Mon Nov 7 06:52:25 2011

5. Go To Home Directory

# cd

Follow the above command to move to direct home directory just typing cd+enter.

If you want to move to diffrent directory follow the below command

# cd /opt

6. Check Current Working Directory

If you want to know where are you working just type the below command to show the current working Directory

# pwd
/home/duser

7. Listing The File And Directory

You can list the all file and directory just typing the below command but it will  show the hidden files.

# ls
ajenti-repo-1.0-1.noarch.rpm aquota.user boot dev home lib media nohup.out proc root selinux sys usr
aquota.group bin cgroup etc index.php lib64 mnt opt reboot sbin srv tmp var

List The File And Directory With Full Detail

Type the below command to know the files and directories with full details.

# ls -l
total 236
dr-xr-xr-x 2 root root 4096 Oct 26 12:13 bin
dr-xr-xr-x 3 root root 4096 Sep 23 2011 boot
drwxr-xr-x 2 root root 4096 Jul 12 2016 cgroup
drwxr-xr-x 8 root root 2180 Jun 10 2016 dev
drwxr-xr-x 101 root root 12288 Feb 6 09:37 etc
drwxr-xr-x 4 root root 4096 Dec 3 2015 home
-rw-r--r-- 1 root root 43 Jun 17 2015 index.php
dr-xr-xr-x 10 root root 4096 Oct 26 12:13 lib
dr-xr-xr-x 10 root root 12288 Oct 26 12:13 lib64
drwxr-xr-x 2 root root 4096 Sep 23 2011 media

To Show The Hidden Files

Type the below command to show the hidden files.

# ls -al
total 244
dr-xr-xr-x 22 root root 4096 Oct 26 11:54 .
dr-xr-xr-x 22 root root 4096 Oct 26 11:54 ..
-rw-r--r-- 1 root root 0 Jul 5 2015 .autofsck
-rw-r--r-- 1 root root 0 Jul 5 2015 .autorelabel
dr-xr-xr-x 2 root root 4096 Oct 26 12:13 bin
dr-xr-xr-x 3 root root 4096 Sep 23 2011 boot
drwxr-xr-x 2 root root 4096 Jul 12 2016 cgroup
drwxr-xr-x 8 root root 2180 Jun 10 2016 dev
drwxr-xr-x 101 root root 12288 Feb 6 09:37 etc
drwxr-xr-x 4 root root 4096 Dec 3 2015 home
-rw-r--r-- 1 root root 43 Jun 17 2015 index.php
dr-xr-xr-x 10 root root 4096 Oct 26 12:13 lib
dr-xr-xr-x 10 root root 12288 Oct 26 12:13 lib64
drwxr-xr-x 2 root root 4096 Sep 23 2011 media

8. To Show The Current Active Processes On System

Follow the below command to check the current active processes on system.

# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 136 0.0 0.0 10680 4 ? S<s 2015 0:00 /sbin/udevd -d
root 483 0.0 0.1 249860 4620 ? Sl 2015 20:16 /sbin/rsyslogd -i /var/run/syslogd.pid -c 5
root 736 0.0 0.1 139176 3500 ? Ss 2015 29:57 /usr/bin/perl -wT /usr/sbin/munin-node
root 967 0.0 0.0 4068 8 tty1 Ss+ 2015 0:00 /sbin/mingetty console
root 997 0.0 0.0 4068 8 tty2 Ss+ 2015 0:00 /sbin/mingetty tty2
root 2583 0.0 0.0 106276 8 ? S 2016 0:00 /bin/sh /usr/local/bin/inotifywait.sh /var/www/chroot/
root 2584 0.0 0.0 24204 1584 ? S 2016 0:12 inotifywait -mrq -e CREATE --format %w%f --exclude .*/tmp /var/www/chroot/
root 2585 0.0 0.0 107300 1552 ? S 2016 2:07 /bin/sh /usr/local/bin/inotifywait.sh /var/www/chroot/
root 4859 0.0 0.1 118164 4528 ? Ss 06:39 0:00 sshd: dsharma-dev [priv]
10093 4861 0.0 0.0 118164 2160 ? S 06:39 0:00 sshd: dsharma-dev@notty
10093 4862 0.0 0.0 118164 1736 ? Ss 06:39 0:00 sshd: dsharma-dev@internal-sftp
apache 5407 0.0 2.0 746924 56324 ? S 06:45 0:02 /usr/sbin/httpd
root 5940 0.0 0.1 118168 4524 ? Ss 06:47 0:00 sshd: dsharma [priv]

9. To Know The All Running Process On System

Follow the below command to see the all running processes on system.

# top
top - 07:41:27 up 583 days, 18:46, 0 users, load average: 0.25, 0.14, 0.08
Tasks: 140 total, 1 running, 139 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.6%us, 0.1%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.1%st
Mem: 2764752k total, 632152k used, 2132600k free, 0k buffers
Swap: 5529504k total, 112652k used, 5416852k free, 298884k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 21328 364 248 S 0.0 0.0 1:08.74 init
136 root 16 -4 10680 4 0 S 0.0 0.0 0:00.02 udevd
483 root 20 0 244m 4624 404 S 0.0 0.2 20:16.61 rsyslogd
736 root 20 0 135m 3500 652 S 0.0 0.1 29:57.26 munin-node
967 root 20 0 4068 8 4 S 0.0 0.0 0:00.00 mingetty
997 root 20 0 4068 8 4 S 0.0 0.0 0:00.00 mingetty
2583 root 20 0 103m 8 4 S 0.0 0.0 0:00.00 inotifywait.sh
2584 root 20 0 24204 1584 240 S 0.0 0.1 0:12.96 inotifywait
2585 root 20 0 104m 1552 392 S 0.0 0.1 2:07.12 inotifywait.sh
4859 root 20 0 115m 4528 3428 S 0.0 0.2 0:00.01 sshd
4861 dsharma- 20 0 115m 2160 992 S 0.0 0.1 0:00.72 sshd
4862 dsharma- 20 0 115m 1736 580 S 0.0 0.1 0:00.44 sshd
5940 root 20 0 115m 4524 3428 S 0.0 0.2 0:00.00 sshd
5942 dsharma 20 0 115m 2052 920 S 0.0 0.1 0:00.01 sshd

10. Killing The Process Using Process ID (PID)

Follow the below command to kill the rsyslogd process use the above command to know the its process id.

# kill 483

11. Removing File From System

As system administrator you always need to remove the unwanted file to clean the system. Follow the below command to remove the files

# rm File_Name

Removing File Forcefully With Verbose Mode

# rm -rvf File_Name

Removing Empty Directory

Follow the below command to remove the empty directory.

# rmdir Directory_Name

Remove The Directory With Its Content

# rm -r Directory_name

12. Creating A File

There are multiple command to create a file usring the terminal.

# touch File_Name
# echo -n > File_Name
# vim File_name
# cat > File_Name
Than type ctrl+D

13. Creating File With Content

Follow the below command to create file with some content.

# echo This is my test file > File_Name

14. Moving A File

Use below command to move files from one directory to another directory.

# mv File1 File2

15. Show Memory Status

If you want to know about system memory status than follow the below command.

# free -m
      total used free shared buffers cached
Mem:  2699  661  2038  237         0 281
-/+ buffers/cache: 379 2320
Swap: 5399 107 5292

In GB

# free -g
     total used free shared buffers cached
Mem:   2      0   2    0     0         0
-/+ buffers/cache: 0 2
Swap: 5 0 5

16. To Know  CPU Information

As a system administrator you always need to know about the the CPU information of new system.
Run the below command to know the CPU Information.

# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 42
model name : Intel(R) Xeon(R) CPU E31270 @ 3.40GHz
stepping : 7
cpu MHz : 3392.227
cache size : 8192 KB
physical id : 0
siblings : 8
core id : 0
cpu cores : 4
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer xsave avx lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid
bogomips : 6784.45
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

processor : 1
vendor_id : GenuineIntel
cpu family : 6
model : 42
model name : Intel(R) Xeon(R) CPU E31270 @ 3.40GHz
stepping : 7
cpu MHz : 3392.227
cache size : 8192 KB
physical id : 0
siblings : 8
core id : 1
cpu cores : 4
apicid : 2
initial apicid : 2
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer xsave avx lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid
bogomips : 6784.45
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

17. To Know Disk Usage

You can check the disk usage in human readable format using the below command.

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/simfs 30G   22G 8.8G   71%   /
none        1.4G 16K 1.4G    1% /dev
tmpfs       512M 52K 512M    1% /var/lib/php/session
/dev/sda1   497M 155M 343M   32% /boot

18. To Know The System Information

Type the below command to know the system information like Kernel Name, Host Name, Kernel Release Number, Processor Type etc.

# uname -a
Linux client1.example.com 2.6.32-042stab081.5 #1 SMP Mon Sep 30 16:52:24 MSK 2013 x86_64 x86_64 x86_64 GNU/Linux

19. Copy File And Directory

Use cp command to copy file and directory. Follow the below command to copy a file.

# cp fine_name /opt/

Run below command to copy a directory. To copy a directory you will need to use -r option.

# cp Download/ /opt/

20. Create New Directory

Use below command to create empty directory.

# mkdir /directory_name    [creating directory under /]

# mkdir directory_name      [creating directory in current path]

# mkdir -p /opt/test/directory_name [creating collaborative directory]

21. Clear Screen 

Follow the below command to clear screen.

# clear

22. Search content in file

# grep test ubuntu

This is my test file

Creating test file

Neo working on test file

In above command we are searching for ” test ” string in ubuntu file.

23. Securely Copy File On Remote Host

# scp my_file.txt [email protected]/root/downlaod/

24. To Shutdown System

Follow the below command to power off the system immediately.

# shutdown -h now

25. To Reboot System

Run the below command to reboot the system.

# reboot

I hope this article will be helpful to understand the Basic Linux Commands. Read our another article Easy Steps to Clone Your HDD (Hard Drive) using dd and /etc/hosts vs. /etc/resolv.conf in Linux. If you have any queries and problem please comment in comment section or you can also ask your question.