Top 23 Linux Commands YOU MUST KNOW !

Linux Operating System is used to run over 90% of all cloud infrastructure and hosting services. For this reason , it's important to be familiar with popular Linux command. I am a Junior Software Engineer , I am using Amazon Linux Machine for demonstration. Let’s get right into it!

What Is a Linux Command?

A Linux command is a program or utility that runs on the command line. A command line is an interface that accepts lines of text and processes them into instructions for your computer.

Before start discussing commands you should know following basic concepts:

Directory : In Linux folder refers to directory.

Arguments :

Argument is an input given as part of commands.

Syntax

  <command> <argument>  
  <command> <argument> <argument>

Example

  [ec2-user@ip-172-31-29-38 ~]$ cd GitDev
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  [ec2-user@ip-172-31-29-38 GitDev]$ touch code.py test.py
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  code.py test.py

Look at the above, command cd GitDev has changed our directory to GitDev and touch code.py test.py created two files for us. These are arguments which are inputs to commands.

Options :

Options modify the default behavior of the command. Generally, they are used to change the output.

Example
```
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  code.py  test.py
  [ec2-user@ip-172-31-29-38 GitDev]$ ls -l
  total 0
  -rw-r--r--. 1 ec2-user ec2-user 0 Mar  4 17:19 code.py
  -rw-r--r--. 1 ec2-user ec2-user 0 Mar  4 17:21 test.py
  [ec2-user@ip-172-31-29-38 GitDev]$ ls --inode
  493092 code.py  493093 test.py
```
By default without option, the ls command lists the contents of the current directory. In the second command, we used the -l option the command displays contents with their properties in a list format. When we use --inode option in third the ls command, the command displays the inode number with the contents.
Absolute Path

An absolute path is the location of a file or directory specified from the root working directory(/). Absolute path is complete path of file.

Example:
```
  [ec2-user@ip-172-31-29-38 ~]$ ls /home/ec2-user/GitDev/
  code.py  test.py
```
In the above example we provided complete path /home/ec2-user/GitDev/ of GitDev directory to list content of directory.
Relative Path

Relative path is defined as path related to the current working directory.

Example :
```
  [ec2-user@ip-172-31-29-38 ~]$ cd GitDev/
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  code.py  test.py
```
In the above example we are changing directory to GitDev using relative path GitDev/. There is no / before argument GitDev which indicates it’s a relative directory to present working directory.

1.pwd

pwd command use to print the current working directory.

[ec2-user@ip-172-31-29-38 ~]$ pwd
/home/ec2-user

Here, my current working directory is /home/ec2-user.

2.ls

ls command use to list the content of directory.

          [ec2-user@ip-172-31-29-38 GitDev]$ ls
          code.py  test.py
          [ec2-user@ip-172-31-29-38 GitDev]$ ls -l
          total 0
          -rw-r--r--. 1 ec2-user ec2-user 0 Mar  4 17:19 code.py
          -rw-r--r--. 1 ec2-user ec2-user 0 Mar  4 17:21 test.py

The ls command lists the contents of the GitDev directory. In the second command, we used the -l option the command displays contents with their properties in a list format.

3.cd

cd command use to change the directory:

Change directory to

Change directory to home (~) directory

  [ec2-user@ip-172-31-29-38 ~]$ pwd
  /home/ec2-user
  [ec2-user@ip-172-31-29-38 ~]$ cd ~
  [ec2-user@ip-172-31-29-38 ~]$ pwd
  /home/ec2-user

change directory to parent (..) directory

  [ec2-user@ip-172-31-29-38 ~]$ pwd
  /home/ec2-user
  [ec2-user@ip-172-31-29-38 ~]$ cd ..
  [ec2-user@ip-172-31-29-38 home]$ pwd
  /home

change directory to previous (-) directory

  [ec2-user@ip-172-31-29-38 home]$ pwd
  /home
  [ec2-user@ip-172-31-29-38 home]$ cd -
  /home/ec2-user

4.touch

touch command use to create file without content.

              [ec2-user@ip-172-31-29-38 GitDev]$ touch code.py test.py
              [ec2-user@ip-172-31-29-38 GitDev]$ ls
              code.py test.py

5.cat

cat command use to display the content o file. It is used to read the data from a file and gives its content as output. It also helps us to create, view, and concatenate files.

[ec2-user@ip-172-31-29-38 ~]$ cat /etc/os-release
NAME="Amazon Linux"
VERSION="2023"
ID="amzn"
ID_LIKE="fedora"
VERSION_ID="2023"
PLATFORM_ID="platform:al2023"
PRETTY_NAME="Amazon Linux 2023"
ANSI_COLOR="0;33"
CPE_NAME="cpe:2.3:o:amazon:amazon_linux:2023"
HOME_URL="https://aws.amazon.com/linux/"
BUG_REPORT_URL="https://github.com/amazonlinux/amazon-linux-2023"
SUPPORT_END="2028-03-15"
[ec2-user@ip-172-31-29-38 ~]$

To concatenate several files, enter:

[ec2-user@ip-172-31-29-38 GitDev]$ touch dev1.py dev2.py
[ec2-user@ip-172-31-29-38 GitDev]$ ls
code.py  dev1.py  dev2.py  test.py
[ec2-user@ip-172-31-29-38 GitDev]$ cat dev1.py dev2.py > final.py
[ec2-user@ip-172-31-29-38 GitDev]$ ls
code.py  dev1.py  dev2.py  final.py  test.py

This command creates a file named final.py that is a copy of dev1.py followed by dev2.py

6.mkdir

mkdir command use to create new directory in the current working directory. The mkdir command allows you to create directories from within the terminal. The default syntax is mkdir followed by the directory name.

[ec2-user@ip-172-31-29-38 ~]$ mkdir GitDev
[ec2-user@ip-172-31-29-38 ~]$ ls
GitDev

You can see ,we have created the GitDev directory.

7.cp

cp command use to copy files and directories from source to desired destination.

Copying Files

The following are examples of coping files

To make copy of file withing the current directory

  [ec2-user@ip-172-31-29-38 GitDev]$ cp code.py copy_code.py
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  code.py  copy_code.py  dev1.py  dev2.py  final.py  test.py

This created copy of code.py file as copy_code.py

To copy a file in your current directory into another directory

  [ec2-user@ip-172-31-29-38 ~]$ cp main.py /home/ec2-user/GitDev
  [ec2-user@ip-172-31-29-38 ~]$ cd GitDev/
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  code.py  copy_code.py  dev1.py  dev2.py  final.py  main.py  test.py

This copied main.py file from current directory to /home/ec2-user/GitDev directory

To copy all the files in a directory to a new directory

  [ec2-user@ip-172-31-29-38 ~]$ cp GitDev/* GitTest
  [ec2-user@ip-172-31-29-38 ~]$ cd GitTest/
  [ec2-user@ip-172-31-29-38 GitTest]$ ls
  code.py  copy_code.py  dev1.py  dev2.py  final.py  main.py  test.py

This copied all files from GitDev directory to GitTest directory.

Copying Directory

To copy all the files from source directory to destination directory

  [ec2-user@ip-172-31-29-38 ~]$ cp -r GitDev GitTest
  [ec2-user@ip-172-31-29-38 ~]$ cd GitTest/
  [ec2-user@ip-172-31-29-38 GitTest]$ ls
  code.py  copy_code.py  dev1.py  dev2.py  final.py  main.py  test.p

8.mv

mv command use to move files and directories from one directory to another or to rename a file or directory

Move files

  [ec2-user@ip-172-31-29-38 ~]$ mv final.py GitDev/
  [ec2-user@ip-172-31-29-38 GitDev]$ ls
  final.py

Here, we moved final.py to GitDev. Use -r(recursively) option to move files more than one.

Rename file

  [ec2-user@ip-172-31-29-38 ~]$ mv main.py new_name.py
  [ec2-user@ip-172-31-29-38 ~]$ ls
  new_name.py

Here, we renamed main.py to new_name.py

9.rm

rm use to delete file from current

[ec2-user@ip-172-31-29-38 ~]$ ls
GitDev  GitTest  main.py
[ec2-user@ip-172-31-29-38 ~]$ rm main.py 
[ec2-user@ip-172-31-29-38 ~]$ ls
GitDev  GitTest

To delete all the files in the mydir directory, one by one, type the following:

[ec2-user@ip-172-31-29-38 ~]$ cd GitDev/
[ec2-user@ip-172-31-29-38 GitDev]$ ls
code.py  copy_code.py  dev1.py  dev2.py  final.py  main.py  test.py
[ec2-user@ip-172-31-29-38 GitDev]$ cd ..
[ec2-user@ip-172-31-29-38 ~]$ rm -i GitDev/*
rm: remove regular empty file 'GitDev/code.py'? y
rm: remove regular empty file 'GitDev/copy_code.py'? yy
rm: remove regular empty file 'GitDev/dev1.py'? y
rm: remove regular empty file 'GitDev/dev2.py'? y
rm: remove regular empty file 'GitDev/final.py'? y 
rm: remove regular empty file 'GitDev/main.py'? y
rm: remove regular empty file 'GitDev/test.py'? y
[ec2-user@ip-172-31-29-38 ~]$ cd GitDev/
[ec2-user@ip-172-31-29-38 GitDev]$ ls

After each file name displays, type y and press Enter to delete the file.

10.rmdir

rmdir command uses to delete directory.

Remove empty directory*GitDev*

  [ec2-user@ip-172-31-29-38 ~]$ rmdir GitDev/
  [ec2-user@ip-172-31-29-38 ~]$ ls
  GitTest

Remove non empty directory*GitTest*

  [ec2-user@ip-172-31-29-38 ~]$ rmdir -r GitTest/
  [ec2-user@ip-172-31-29-38 ~]$ ls

12. find

find command use to find the file in directory.

Syntax : find directory_path -name file_name

Here directory_path is path of directory where you want search file.

ec2-user@ip-172-31-28-71 ~]$ find . -name main.py
./GitDev/main.py

In the above command searches file main.py in current directory.

[ec2-user@ip-172-31-28-71 ~]$ find . -name *.py    
./GitDev/main.py
./GitDev/test.py

In the above command searches all the which file name ends with .py in current directory.

13.grep

grep command use to search lines in file matching pattern.

[ec2-user@ip-172-31-28-71 ~]$ cat main.py    
# This program adds two numbers
num1 = 1.5
num2 = 6.3
# Add two numbers
sum = num1 + num2
# Display the sum
print('The sum of {0} and {1} is {2}'.format(num1, num2, sum))
[ec2-user@ip-172-31-29-58 ~]$ grep -i "num" main.py 
# This program adds two numbers
num1 = 1.5
num2 = 6.3
# Add two numbers
sum = num1 + num2
print('The sum of {0} and {1} is {2}'.format(num1, num2, sum))
[ec2-user@ip-172-31-29-58 ~]$ grep -c "num" main.py 
6

The -i option enables to search for a string case insensitively in the given file. It matches the words "num" ,"num1", "num2". We can find the number of lines that matches the given string/pattern using option -c.

14.awk

awk command use for pattern search and processing.

What operations awk command can do?

Scanning files line by line
Splitting each input line into fields
Comparing input lines and fields to patterns

Performing specified actions on matching lines

  [ec2-user@ip-172-31-28-71 ~]$ cat main.py    
  # This program adds two numbers
  num1 = 1.5
  num2 = 6.3
  # Add two numbers
  sum = num1 + num2
  # Display the sum
  print('The sum of {0} and {1} is {2}'.format(num1, num2, sum))
  [ec2-user@ip-172-31-29-58 ~]$  awk '/num/ {print}' main.py 
  # This program adds two numbers
  num1 = 1.5
  num2 = 6.3
  # Add two numbers
  sum = num1 + num2
  print('The sum of {0} and {1} is {2}'.format(num1, num2, sum))
  [ec2-user@ip-172-31-29-58 ~]$ awk '{print $1,$4}' main.py 
  # adds
  num1 
  num2 
  # numbers
  sum +
  # sum
  print('The {0}

awk '/num/ {print}' main.py this prints the lines which match the given pattern. awk '{print $1,$4}' main.py splitting a line into two fields $1 and $4.

15.df

df command is used to see the storage usage by different file system directories (technical term here is file system mounts).This displays information about total space and available space on a file system.

[ec2-user@ip-172-31-28-71 ~]$ df
Filesystem     1K-blocks    Used Available Use% Mounted on
devtmpfs            4096       0      4096   0% /dev
tmpfs             486172       0    486172   0% /dev/shm
tmpfs             194472    2880    191592   2% /run
/dev/xvda1       8310764 1591284   6719480  20% /
tmpfs             486172       0    486172   0% /tmp
/dev/xvda128       10202    1310      8892  13% /boot/efi
tmpfs              97232       0     97232   0% /run/user/1000

16.du

du command use to print disk usage in MB Gb. This displays the number of blocks used for files.

Exit Status:

This command returns the following exit values:

Item	Description
0	Successful completion.
\>0	An error occurred.

[ec2-user@ip-172-31-28-71 ~]$ du
4       ./.ssh
12      ./GitDev
36      .

This displays the number of disk blocks in the current directory and each of its subdirectories.

17.lscpu

lscpu command use to print CPU information. The lscpu command in Linux with the -J argument generates the output in JSON format.

[ec2-user@ip-172-31-28-71 ~]$ lscpu -J
{
   "lscpu": [
      {
         "field": "Architecture:",
         "data": "x86_64",
         "children": [
            {
               "field": "CPU op-mode(s):",
               "data": "32-bit, 64-bit"
            },{
               "field": "Address sizes:",
               "data": "46 bits physical, 48 bits virtual"
            },{
               "field": "Byte Order:",
               "data": "Little Endian"
               }
     ]
}
MORE

18.ps

ps command use to get the information of processes. Processes need system resources like CPU, Physical memory etc. to stay alive.ps is a powerful tool that allows you to view information about the processes running on your Linux system. It helps monitor running processes, identify process ID (PID), terminal type (TTY), CPU time usage, command name, user ID and other information.

ps -ef or ps -aux*− List currently running processes in full format*

[ec2-user@ip-172-31-28-71 ~]$ ps -ef
UID          PID    PPID  C STIME TTY          TIME CMD
root           1       0  0 Mar06 ?        00:00:05 /usr/lib/systemd/systemd --switched-root --system --deserialize=32
root           2       0  0 Mar06 ?        00:00:00 [kthreadd]
root           3       2  0 Mar06 ?        00:00:00 [rcu_gp]
root           4       2  0 Mar06 ?        00:00:00 [rcu_par_gp]
root           5       2  0 Mar06 ?        00:00:00 [slub_flushwq]
root           6       2  0 Mar06 ?        00:00:00 [netns]
MORE

19.Kill

Kill command use to kill process.

Syntax : kill -9 process_id or process_name

[ec2-user@ip-172-31-28-71 ~]$ ps -ef | grep http
root       59143       1  0 16:57 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache     59164   59143  0 16:57 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache     59165   59143  0 16:57 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache     59166   59143  0 16:57 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache     59167   59143  0 16:57 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
ec2-user   62502   38348  0 17:03 pts/0    00:00:00 grep --color=auto http
[ec2-user@ip-172-31-28-71 ~]$ sudo kill -9 59164
[ec2-user@ip-172-31-28-71 ~]$

This kills process apache which has process id 59143. You can get process ids from ps command.

20.netstat

netstat -an command that there’s indeed a process listening on ports. This command helps to check things about how your computer connects to the internet. netstat stands for network statistics.

[ec2-user@ip-172-31-29-58 ~]$ netstat -a | more 
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 0.0.0.0:ssh             0.0.0.0:*               LISTEN     
tcp        0      0 ip-172-31-29-58.us-:ssh ec2-18-237-140-16:52390 ESTABLISHED
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN     
udp        0      0 ip-172-31-29-58.:bootpc 0.0.0.0:*                          
udp        0      0 localhost:323           0.0.0.0:*                          
udp6       0      0 ip-172-31:dhcpv6-client [::]:*                             
udp6       0      0 localhost6:323          [::]:*                             
raw6       0      0 [::]:ipv6-icmp          [::]:*                  7          
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  3      [ ]         STREAM     CONNECTED     18595    
unix  3      [ ]         STREAM     CONNECTED     18690    /run/systemd/journal/stdout
unix  3      [ ]         STREAM     CONNECTED     16002    
unix  2      [ ACC ]     STREAM     LISTENING     14501    /run/systemd/resolve/io.systemd.Resolve
unix  2      [ ACC ]     STREAM     LISTENING     14506    /run/systemd/resolve/io.systemd.Resolve.Monitor
--More--

netstat -a | more show both listening and non-listening sockets. With the –interfaces option, show interfaces that are not up.

21.ifconfig

ifconfig command find the IP addresses. Configures or displays network interface parameters for a network by using TCP/IP.

[ec2-user@ip-172-31-28-71 ~]$ ifconfig
enX0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9001
        inet 172.31.28.71  netmask 255.255.240.0  broadcast 172.31.31.255
        inet6 fe80::49:54ff:fec4:c79d  prefixlen 64  scopeid 0x20<link>
        ether 02:49:54:c4:c7:9d  txqueuelen 1000  (Ethernet)
        RX packets 48407  bytes 32785275 (31.2 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 31357  bytes 3158831 (3.0 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 12  bytes 1020 (1020.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 12  bytes 1020 (1020.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[ec2-user@ip-172-31-28-71 ~]$

22.tcpdump

tcpdump command can be used to find all communications (aka network packages) happening through your network (coming in or going out of your machine)

23.ping

ping is a network utility tool and helps to check if a particular IP address is reachable

[ec2-user@ip-172-31-28-71 ~]$ ping google.com
PING google.com (142.250.217.110) 56(84) bytes of data.
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=1 ttl=58 time=7.77 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=2 ttl=58 time=7.82 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=3 ttl=58 time=7.90 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=4 ttl=58 time=7.87 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=5 ttl=58 time=7.86 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=6 ttl=58 time=7.79 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=7 ttl=58 time=7.83 ms
64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=8 ttl=58 time=7.82 ms
^C
--- google.com ping statistics ---
8 packets transmitted, 8 received, 0% packet loss, time 7012ms
rtt min/avg/max/mdev = 7.769/7.832/7.900/0.040 ms
[ec2-user@ip-172-31-28-71 ~]$ ping git.com
PING git.com (44.233.224.228) 56(84) bytes of data.
^C
--- git.com ping statistics ---
56 packets transmitted, 0 received, 100% packet loss, time 57168ms

[ec2-user@ip-172-31-28-71 ~]$

Top 23 Linux Commands YOU MUST KNOW !

What Is a Linux Command?

1.pwd

2.ls

3.cd

4.touch

5.cat

6.mkdir

7.cp

8.mv

9.rm

10.rmdir

12. find

13.grep

14.awk

15.df

16.du

17.lscpu

18.ps

19.Kill

20.netstat

21.ifconfig

22.tcpdump

23.ping

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Command Palette

What Is a Linux Command?

1.pwd

2.ls

3.cd

4.touch

5.cat

6.mkdir

7.cp

8.mv

9.rm

10.rmdir

12. find

13.grep

14.awk

15.df

16.du

17.lscpu

18.ps

19.Kill

20.netstat

21.ifconfig

22.tcpdump

23.ping

Comments

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