The Ultimate Linux Cheatsheet

This content originally appeared on DEV Community and was authored by Ayesha Sahar

What is Linux?

From desktops to supercomputers, Linux is everywhere! You must have heard of it at least once, right? But the question is, what is Linux?

Just like Windows and Mac, it is an operating system and has been around since the 1990s. Linux is basically a Unix-like, Kernal based, fully-memory protected, multitasking operating system. It is open-source software that runs on a wide range of hardware, from PCs to even Macs.

What are Linux Commands?

A command is a program that interacts with the kernel to provide the environment and perform the functions called for by the user. A command can be:

• a built-in shell command

• an executable shell file, known as a shell script

• a source compiled, object code file.

Basic Linux Commands

Here are a lot of basic Linux commands you can try! I wanted to write "some of" but these are too many to be classified as "some".

Disclaimer: Some commands may not work for you correctly due to issues like missing packages, differences in versions, etc. I did list some alternatives, but if they don't work too, then I'll just tell you what our course instructor tells us to do: Google it!

1. history

Just type "history" in the terminal and it will show you a list of all commands you have used.

2. clear

Just type "clear" in the terminal and the terminal will be cleared.

3. up OR down key

Use these keys to move back and forth between the commands you have previously used.

4. pwd

It is a short form for the present working directory. It shows the folder you are currently working in.

5. man man

This command shows a manual of all the commands.

You can use:

man command

to get information about a particular command.

6. ls

This command shows all the directories and files in the pwd.

7. ls -al

This command prints all the additional information of all files and directories.

8. ls -R

This command prints out the sub-directories of a directory too.

8. ls -a

This command prints out the hidden files.

9. dir

This command prints out all available directories in the pwd.

10. cd

It is used to change directories. Whenever you open the terminal, the current directory would be home.

For example:

The command

cd Desktop

will let you enter the Desktop. Now if you check the pwd, it will be Desktop.

Just use:

cd

to get back to the home directory.

11. mkdir

This command makes a new directory.

For example:

mkdir Linux

This command will make a new directory named Linux in the pwd.

12. sudo -i OR sudo -s OR sudo su

Use one of these 3 commands login as root user.

13. exit OR logout

You can logout or exit the root.

14. rm FileName.txt

Use this command to remove/del file from a directory.

15. rmdir DirectoryName

It is used to remove/del an empty directory.

15. touch

It is used to create a new file or to change the timestamp of an existing file.

16. stat file.txt

Use this command to check details of any file.

17. cat > file.txt

It creates and adds data in a file. Use CTRL+d after you finish adding data to save the file.

18. cat file.txt

It shows the contents of the file.

19. cat file1.txt file2.txt > file.txt3

It adds the data of existing files, "file1" and "file2", to a new file, "file3".

20. cp

You can copy a file or a folder using this command.

Use:

cp file.txt Directory

to copy a file to your desired directory. Please note that in order to do so, your pwd must be the directory the file is currently in.

Use:

cp FolderName -r Directory

to copy a folder/directory to another directory.

21. mv

It will move files inside your system.

Syntax:

mv FileName.txt Directory

22. head

This command prints the first ten lines of a file.

Syntax:

head FileName.txt

23. tail

This command prints the last ten lines of a file.

Syntax:

tail FileName.txt

24. uname

This command gives the name of your Linux.

25. uname -a

This command gives detailed information about your Linux.

26. wget

Use:

wget url

to download anything from the internet.

27. apt -get OR apt

Use:

sudo apt install PackageName

*or *

sudo apt -get install PackageName

to install any package .

28. remove

Use:

sudo apt remove PackageName

to remove/uninstall any package.

29. grep

You can search for a pattern in which specific words lie.

cat file.txt | grep hi

This command will search for "hi" in the text file mentioned and will highlight where it found "hi".

30. ps

It gives the list of current processes.

31. gzip

It is used to zip any file.

Syntax:

gzip FileName.txt

31. gunzip

It is used to unzip any file.

Syntax:

gunzip FileName.txt

33. compress

It is used to compress data.

34. uncompress

It is used to uncompress data.

35. cpio

It stores files on tapes.to/ from archives.

36. tar

It is used archive files and directories and can store them on tapes.

37. zip

It is used to compress a file to .zip file.

37. unzip

It is used to uncompress a file.

38. hostname

It is used to print hostname on the terminal.

39. ping

It is used to check connectivity to a server.

e.g. ping youtube.com

will ping to youtube and then print the response time.

40. w

This command displays the user details that are currently logged in the system.

41. cal

It displays the calendar for the current month.

42. date

It displays the date and time.

43. date -u

It displays the date and universal time.

44. whoami

It displays the current user name.

45. echo

To understand this, let's see an example:

echo name

This command will return "name" as the output.

46. wc

It counts the number of lines, number of words, and number of characters. Then it displays the result in the same sequence.

Syntax:

wc file.txt

47. wc -l

It counts and displays the number of lines of a file.

Syntax:

wc -l file.txt

48. wc -w

It counts and displays the number of words of a file.

Syntax:

wc -w file.txt

49. CTRL+shift+c

Used for copying.

50. CTRL+shift+v

Used for pasting.

51. sudo

Using sudo allows a normal user to execute a command with root privilege.

52. sudo get apt update

It is used to update the whole system.

53. locate

Let's see an example to understand it's function.

locate hi

This command will list out all files or paths with "hi" in their path or file names.

54. locate -c

Let's see an example to understand it's function.

locate hi

This command will list out the number of files with "hi" in their path or file names.

55. ls -l

This command shows a list of all users along with their default permissions.

56. sort

It sorts a file alphabetically.

57. uniq

It removes duplicate lines from a sorted file.

58. sleep

Produces a delay for a specified amount of time.

59. diff

This command shows differences between files.

Syntax:

diff file1.txt file2.txt

60. cut

It removes sections from each line of files.

61. cmp

It compares two files.

Syntax:

cmp file1.txt file2.txt

62. whereis

It locates the binary and man page files for a command.

63. which

It shows full path of where commands reside.

64. md5sum

It prints the MD5 Checksum.

65. mv to rename a file

Use:

mv abc.txt def.txt

to rename a file. Here the name of the file, abc, is changed to def.

66. echo to append text

Use:

echo "Enter your text here" >> file.txt

to append any text to the end of your specified file.

File Editors in Linux

Here are 4 file editors in Linux:

67. emacs

This command opens a full-screen editor.

68. pico

This command opens a simple editor.

69. gedit

This command opens a GUI text editor.

70. vim OR vi

You can use either command to open vim.

• The command "i" will let you open insert mode.

• To exit vim: Press esc keyt + :q

• To save file: Press esc keyt + :w FileName.txt

Creating and Setting Passwords for User and Groups

By using the following commands, you can create and set passwords for users and groups!

71. useradd OR adduser

Either of these may work for you. They add another user in the system. Execute this command while logged into root. If not in root, use sudo before it.

Syntax:

useradd NewUser

72. passwd

It is used to set password for a user. Works only when you are logged in as root or use sudo before it.

Syntax:

passwd NewUser

73. userdel

It is used to delete a user. Works only when you are logged in as root or use sudo before it.

Syntax:

userdel NewUser

74. cat /etc/passwd

It shows a list of all ubuntu users. Works only when you are logged in as root.

75. groupadd

It is used to add a group. Works only when you are logged in as root.

76. gpasswd

It is used to set password for a group. Works only when you are logged in as root.

77. Adding users to a group

The following command creates a new user and a new group. Then adds that user to the group.

Syntax:

sudo adduser UserName GroupName

78. groupdel

It is used to delete a group.

Syntax:

groupdel GroupName OR sudo groupdel GroupName

79. Add existing user to an existing group

Use the following command to perform this task:

sudo usermod -a -G GroupName UserName

80. compgen -g OR cat /etc/group

Either of them can be used to see the list of all users and groups.

81. Granting sudo privilege to a new user

After you create a new user via the terminal, that user would not be able to do anything even while using sudo. That is because the user does not have the sudo privilege.

Use this command to add that user to the group of sudo users or in other words, to grant that user the sudo privilege:

sudo usermod -aG sudo UserName

Setting Ownerships and Permissions for Files/Directories

By using the following commands, you can set ownership and permissions for files/directories.

82. Setting ownership of files

Login to the user who created the file whose ownership you want to modify. For example, user Ayesha created the file, abc.txt. You want to modify the ownership of abc.txt. Now login to Ayesha. You want to make another user, Sahar, the owner too. Use the following command to achieve this:

sudo chown Sahar abc.txt

83. Setting file/folder permissions

There are two types of permissions;

1. Alphabetic:

• read (r)

• write (w)

• execute (x)

2. Numeric:

• write: 2

• read: 4

• execute: 1

• no permission: 0

Alphabetic permissions are quite simple. Let's understand the numeric permissions.

For example:

chmod 561 abc.txt

We use chmod to set permissions. Here we are setting permission on abc.txt

You might be thinking, why are there 3 numbers?

That is because:

• 5 is the permission for user.

• 6 is the permission for group.

• 1 is the permission for others.

When setting permissions we do it for the above-mentioned 3 types.

Here, another question might come to your mind; how were those numbers calculated????

• We granted the read(4) and execute(1) permissions to user. Therefore 4+1 =5.

• We granted the read(4), write(2), and execute(1) permissions to group. Therefore 4+2+1 =6.

• To others, we only granted the execute permission, hence the 1.

File System Management Commands

Here are some commands used for filesystem management!

84. badblocks

This command is used to search for bad blocks (block of memory which has been corrupted and can no longer be used reliably) in your linux.

85. df

It shows the free disk space on one or more filesystems.

86. du

It shows how much disk space a directory and all it's files contain.

87. fsck

It checks the filesystem. Do not run this command on a mounted filesystem.

Syntax:

fsck filesystem

88. sync

This command sunchronizes data on disk with memory. It only writes the buffered data to the disk.

89. mount

It is used to mount a filesystem.

Syntax:

mount filesystem

90. unmount

It is used to unmount a filesystem.

Syntax:

unmount filesystem

91. Fg

It is used to continue a program which was stopped and bring it to the foreground. For example, you stopped a music player, p, with the command Ctrl+z. In order to let it continue, write the command; fg p.

Syntax:

fg taskname

92. Top

It informs the user about all the running processes on the Linux.

93. PS

It stands for ‘Process Status’. This is similar to the “Task Manager” that pop-ups in a Windows Machine when we use Ctrl+Alt+Del. It is similar to the “top” command but the information displayed is different.

• To check all the processes running under a user:

ps ux

• To check the process status of a single process:

ps PID

94. Kill

It is used to terminate any running processes on a Linux machine. PID (process id) of the process you want to kill must be known.

• You can find PID by this command:

pidof ProcessName

• You can kill a process by this command:

kill PID

95. NICE

Running a lot of processes at a time can slow down the speed of some high priority processes and result in poor performance. To avoid this situation, you can tell your machine to prioritize processes as per your requirements.

This priority is called Niceness in Linux (has a value between -20 to 19). The lower the Niceness index, the higher would be a priority given to that task. The default value of all the processes is 0.

• To start a process with a niceness value other than the default value use the following syntax:

nice -n 'Nice value' ProcessName

• If there is some process already running on the system, then you can ‘Renice’ its value using syntax.

renice 'nice value' -p 'PID'

Network Management Commands

Following commands are used to manage networks.

96. ifconfig

ifconfig stands for interface configurator. It is used to initialize an interface, configure it with an IP address, and enable or disable it. It is also used to display the route and the network interface. Basic information displayed upon using ifconfig; IP address, MAC address and MTU (Maximum Transmission Unit). This is how we can get the IP address of 3 networks; Ethernet, local network, and WLAN.

• ifconfig eth0
• ifconfig lo
• ifconfig wlan0

97. ip

This is the latest and updated version of ifconfig command. “ip a” gives the details of all networks like ifconfig. “ip addr” can also be used to get the details of a specific interface. This is how we can get the IP address of 3 networks; Ethernet, local network, and WLAN.

• ip a show eth0
• ip a show lo
• ip a show wlan0

98. ip link

This command is used for configuring, adding, and deleting network interfaces. Use ip link show command to display all network interfaces on the system.

99. iftop

This command is used in traffic monitoring. You can view the ports using the -P option in command like this:

• sudo iftop -P

You can use the -B command to get the data in bytes, instead of bits (which is shown by default).

• iftop -B

100. tracepath

Linux tracepath is similar to traceroute command. It is used to detect network delays. However, it doesn't require root privileges. It is installed in Ubuntu by default.

It traces the route to the specified destination and identifies each hop in it. If your network is weak, it recognizes the point where the network is weak.

• tracepath google.com

101. traceroute

It is used to troubleshoot the network. It detects the delay and determines the pathway to your target. It provides the names and identifies every device on the path, follows the route to the destination and determines where the network latency comes from and reports it.

• traceroute google.com

To avoid the reverse DNS lookup, add -n in the command syntax.

• traceroute -n google.com

The output indicates the network delays. The asterisks shown in the output indicates a potential problem in reaching that host. They indicate the packet loss during communication to the network.

Generally, the traceroute command sends UDP packets. It can as well send TCP or ICMP packets. To specifically send in ICMP, use this command:

• sudo traceroute -I google.com

To send a variant of TCP, use this command:

• sudo traceroute -T google.com

102. host

Linux host command displays the domain name for a given IP address and IP address for a given hostname. It is also used to fetch DNS lookup for DNS related query.

• host thecodingcompany.hashnode.dev
• host 149.77.21.18

You can combine the host command with -t, and get DNS resource records like SOA, NS, A, PTR, CNAME, MX, SRV.

• host -t

103. mtr

This command is a combination of ping and the traceroute command. It continuously displays information regarding the packets sent with the ping time of each hop. It is also used to view the network issues.

Syntax:

mtr

Example:

mtr google.com

You can use mtr with –report option. It sends 10 packets to each hop that is found on the way.

104. whois

This command is used to fetch all the information related to a website. You can get all the information about a website including the registration and the owner information.

Syntax:

whois websiteName

Example:

whois google.com

105. ifplugstatus

This command is used to check if a cable is plugged into the network interface.

• ifplugstatus

If the output is "link beat detected", this means that the cable is plugged in.

106. dnsdomainname

This command shows the system's dns domain name.

107. hostname

This command is used to show or set the name of your machine for networking.

108. nisdomainname

This command is used to show or set the system's NIS/YP domain name.

109. arp

This program lets the user read or modify their arp cache.

110. dig

This command sends domain name query packets to name servers for debugging or testing.

111. ifdown

This command disables a network interface, placing it in a state where it cannot transmit or receive data.

Syntax:

ifdown eth0

112. ifup

This command enables a network interface, placing it in a state where it can transmit or receive data.

Syntax:

ifup eth0

113. showmount

This command shows mount information for an NFS server.

Conclusion

Ooops, this turned out to be a very long article😅 But I hope you guys find it useful. Linux may seem tough and scary but deep down, he's a good kid. Just put an effort and you'll surely find these commands and Linux in general easy in no time!

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This content originally appeared on DEV Community and was authored by Ayesha Sahar