20 Lesser known useful Linux commands (with explanation + examples):

1. nl command

The nl command in linux stands for number lines. If you ever had a large text document and needed to add lines to it, the nl command is your best friend.

Rather than going through the time-consuming process of manually numbering each line , you can simply use nl from the command line and be done in a matter of seconds.

2. pstree

This command displays all of the processes that are currently running, along with their associated child processes, in a tree-like format similar to the output of the 'tree' command:


3. lsd

lsd is the next-generation ls command. Try lsd instead of ls to list files in a directory. This project is a rewrite of GNU ls with many new features such as colors, icons, a tree-view, more formatting options, and so on:


4. stat

In Linux, the stat command displays file or filesystem status information. The stat displays a wealth of information about the file passed as an argument.

The stat command displays the following infomation about a file:

- File Size
- Blocks
- Access Permission
- Date and Time of Last Access, Modify, Change, and so on:

$ stat distros.txt

5. lsb_release

provides certain LSB (Linux Standard Base) and distribution-specific information. If this package is not installed on your system you may need to install  it  first using your distro package manager.

$ lsb_release -a


6. ss

Unlike the deprecated netstat command, the'ss' command is mostly used by sysadmins to dump network socket statics and display the information in a simpler, faster, and human readable format.

It has the ability to display more TCP and state information than other tools.


7. last

When managing a multiuser system, you'll frequently need to know who, when, and from where people are logging in.

last is a command-line utility that displays information about system users' most recent login sessions.

It is extremely useful when tracking user activity or investigating a possible security breach:

$ last

8. exa

exa is another cool replacement for the venerable file-listing command-line program ls that comes with Unix and Linux operating systems, adding features and improving defaults. It uses colors to differentiate between file types and metadata.

It is familiar with symlinks, extended attributes, and Git. It's also small, fast, and only has one binary.

Exa attempts to be a more feature-rich, user-friendly version of ls by deliberately making some decisions differently.

Here is an example  of using exa to  display a tree of files, three levels deep, as well as each file’s metadata.

$ exa --long --tree --level=3


9. nc -zv localhost <port>

You can make use of netcat to check which ports are open on your system:


10. > file.txt

This command clears the contents of a file without the need to delete and recreate the file. This command is very useful in scripting when we need to log data on the same file repeatedly.


11. tac

Similar to the cat command, the tac command concatenate and print files contents  in reverse order. You can tell from the name that this command is the reverse version of the popular cat command.

$ tac distros.txt


<space> command

Every command you type in the terminal is saved in the history and can be retrieved using the history command.


What if you don't want it to be placed in history for security reasons? Yes, you can do it, and it is very simple. Simply enter one or more white spaces before entering a command in the terminal, and your command will not be recorded.


14. batcat

Instead of using the cat command to view source code files, try the batcat command, which is a modern version of cat that includes syntax highlighting for many programming languages out of the box.

15. ^foor^bar

You can use the ^foor^bar command to edit the command you ran previously and execute it again. This is very useful if want to correcting typos or mistakes on previous commands:

$ sodu mkdir demo
$ ^sodu^sudo

This will replace "sodu" with "sudo" and re-rerun the command.

16. nohup

If you run the program in a terminal, it will be terminated as soon as your terminal session ends. To avoid this and keep the program running, use the nohup command, which stands for "no hangup."

For example, to compress large amount of data using tar command and ensure that the compression continues even if you close the terminal window accidentally, use the following command:

$  nohup tar -cf archive.tar logs.txt app.jar


The nohup command also creates a file named nohup.out to store the command's output.

17. tldr

The TLDR (Too Long; Didn't Read) pages provides a summarized practical usage of Linux commands. They simplify man pages by providing practical examples.

This tool is useful when you only want to check the syntax of a few common commands without having to scroll through a detailed manpage.

$ tldr exa

18. btop++

An excellent replacement for top/htop written in C++. Btop++ is a resource monitor that displays statistics and usage information for the processor, memory, disks, network, and processes.

29. duf

If you need a good replacement for the du command, the duf command is your best bet. Duff has the following capabilities:

- Colorful, user-friendly output
- Adapts to the theme and width of your terminal
- Sort the results based on your requirements
- etc


20. r

You can also "r" command to  Re-run last executed commands in Linux.

This command  will save you a couple of keystrokes as compared to other alternative ways.

r is a ZSH builtin, so this only works with ZSH.


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Input, Output, and Error Redirection in Linux explained (with examples):

Most Unix/Linux system commands accept input from your terminal and return the resulting output to it.

A command normally reads its input from the standard input, which is usually your terminal.

Similarly, by default, a command writes its output to standard output, which is your terminal.

The concept of redirection refers to the ability to redirect stdin, stdout, and stderr from their usual output locations to another file or command (or even peripheral devices).

When a program is executed in Bash or other Linux shells, it uses 3 different I/O streams. Each stream is represented by a numerical file descriptor.

Here are the standard Linux I/O streams:

• 0 - stdin, the standard input stream.
• 1 - stdout, the standard output stream.
• 2 - stderr, the standard error stream.

A file descriptor is basically a number that uniquely identifies an open file in a computer's operating system.

The input stream sends data to the program, typically by typing on the keyboard.

The program output is directed to the standard output stream, while program error messages are directed to the standard error stream.

Both the input and error streams are printed on the terminal screen by default.

Using the piping technique, the output of another program can be directed to the input stream of another program and act as the standard input.

Redirecting Standard Output (STDOUT)

Redirection is a method of capturing a program's output and sending it as input to another program or file.

The n> operator, where n is the file descriptor number, can be used to redirect streams.

When n is not specified, the standard output stream is used. The following two commands, for example, are identical; both will redirect the command output (stdout) to a file.

$ echo "Linux is the future" > linux.txt
$ echo "Linux is the future" 1> linux.txt


If you want to redirect the standard error (stderr) to a file using the file descriptor of 2 and the >. Here is an example:

$ ping badhost.com 2> error.txt

This will redirect the errors produced by the above command to a file called error.txt.


Both stderr and stdout can be written into separate files. Here is an example:

$ cmd 2> error.txt > output.txt

This will redirect the errors produced by the cmd command to the error.txt file and the output produced to the output.txt file.


In most cases, you may not want to log the error messages to a file or standard error; instead, redirect stderr to a special location on your Linux system called /dev/null:

Here is an example of how you can do it:

$ cmd 2>/dev/null


Redirecting stderr to stdout

When storing the program's output to a file, it's usual practice to redirect stderr to stdout so that everything goes into a single file.

Use the following command to redirect stderr to stdout and have error messages written to the same file as the standard output:

$ cmd > file.txt 2>&1

> file redirects stdout to file.txt, and 2>&1 redirects stderr to the current stdout location.


It is important to note that the order of redirection is crucial. The following example, for example, redirects only stdout to the file. This occurs because STDERR is redirected to STDOUT before STDOUT is redirected to the file.

$ cmd 2>&1 > file


The &> construct can also be used to redirect stderr to stdout. &> has the same meaning in Bash as 2>&1:

$ cmd &> file.txt


The input redirection

You can use stdin redirection to pass the contents of a text file to a command.
Stdin is rarely used. Because most Linux commands accept filenames as arguments, stdin redirection is often unnecessary.

Here is an example of input redirection in use:

$ wc < file.txt

Though stdin is rarely used, it is preferable to pipe, especially to avoid the needless use of the cat command.


Many people would, for example, use the preceding example with cat and then pipe the output of cat to the second command to act as in the input. To be honest, there is no need to use the cat command here.

$ cat file.txt | wc


For a more in-depth guide on how to use command line redirections, check out this article on our website.

Bash Command Line Chain Operators in Linux with Examples:
https://linuxopsys.com/topics/bash-chain-operators-in-linux

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12 destructive Linux terminal commands every Linux user must be aware of (don't run these):

1. Recursive deletion 🔁🗑️

This is one of the scariest commands. When you run this command, it deletes everything in the root directory forcibly and recursively. As a result, all of your directories and subdirectories will be deleted, and all of your data will be lost.


2. Implode hard drive 🕳️

This command will move all data to a special location in Linux known as the black hole, which is located in your system at /dev/null.

Everything that is moved to this location is destroyed.
As a result, if you accidentally move your data to this folder, it will not be recovered


3. The fork bomb 🍴💣

This is my personal best, a simple bash recursive function that, when executed, creates copies of itself, which in turn creates another set of copies of itself. This takes up CPU time and memory. As a result, it loops until the system freezes.


Fortunately, you can defend against this attack by limiting the number of processes run by users to around 4000.

You can accomplish this by issuing the following command:

$ ulimit -S -u 4000


4. Overwrite the hard drive ✍️💿

This command writes raw data (command output) to the specified partition. This causes data loss on the hard drive or specified partition.

command - this could be any Linux command.


5. Blindly download and execute malicious script ☠️📜

Wget and curl are useful Linux commands for retrieving and downloading files from the internet. However, if we blindly download and execute a malicious script, these commands can be dangerous.


Please keep in mind the source from which you are downloading packages and scripts. Use only scripts or applications downloaded from a reputable source.

6. Breach the System 🔓

This command does not physically affect your system in the same way that the other commands do, but it does provide a security breach on the system.


The chmod command changes file permissions to configure user access to a specific file or directory.

By running this command, you grant all system users the ability to read, write, and execute data on your system. In terms of security, this is risky and dangerous.

7. The hidden recursive deletion (rm -rf /) 🔁🗑️

The following command is the same as the previously mentioned rm -rf / command. The codes are hidden in hex here to fool an unsuspecting user.

Running the code below in your terminal will delete your root partition leaving your system unusable.


8. Unknowingly format a hard drive 🧹📀

This command will erase your hard drive and recreate it.
These should only be used when you have a backup of your data on the cloud or an external device.


9. Write random junk to hard drive 🈳📀

This command will write random garbage data to your hard drive.
Your system will not be recovered as a result of this command.


10. Re-running all the history commands 🔁📜

Because it executes every command from that you have already executed, the history | sh command can be dangerous. The action may cause system instability and the execution of commands that you do not want to repeat.


11. The ^foo^bar Command 📜

The ^foo^bar command has the potential to be both helpful and dangerous. While the command saves time by allowing you to edit a previously run command and re-run it,

it can also cause problems if you don't thoroughly check the changes you make before running it.

The command changes the first occurrence of foo to bar.



12. Blindly deleting the crontabs 🤖📜

The crontab command aids in the automation of routine tasks. All commands and instructions, however, are saved in a single crontab file, which can be removed by using the -r option and the crontab command.

This can happen if you want to specify the -e flag but accidentally type -r. There is no yes/no prompt before removing the file, so be cautious.

Make a backup of your crontab file because there aren't many recovery options if it gets deleted.



Please DO NOT run any of the above commands in your Linux terminal or shell, or on the computers of your friends or coworkers. Run them in a virtual machine if you want to test them.

Any inconsistency or data loss caused by the execution of the preceding command will bring your system to a halt.

That's a wrap!

Thank you for taking your time to read our thread.

If you know of any other dangerous Linux commands that I have missed, please leave them in the comments.

And be sure to rt, like and follow us (@linuxopsys) for more future Linux content.

When writing Bash scripts, you will frequently need to stop the execution of a script when a certain condition is met or perfom some actions based on a command's exit code.

In this thread I will go over the built-in bash exit command as well as the exit statuses of the commands that have been executed.

Exit Status

When a shell command exits, whether successfully without any errors or unsuccessfully with errors , it returns an exit code.

An exit code of zero indicates that the command completed properly without any errors, while a non-zero indicates that an error occurred.

The $?  is a special shell variable that stores the exit status of the most recently run command:

$ echo $?

Because the batcat command completed successfully and without error, the exit code is zero, as expected.

If you attempt to run batcat command on an not-existing file, the exit code will be non-zero as shown below:

$ batcat nullfile

The command's status code can be used for debugging and to determine why it failed. The man pages for each command include information about the exit codes.

When chaining commands using pipes, the exist status code is that of the last command in the chain.

$ ls -lah | head -n 3

In the preceding example, echo $? prints the exit code of the head command and its zero. To prove this, execute the ls command on a non-existent directory.

Here you can see the ls command fails but we still get the status code of zero.

$ ls -lah nulldir | head -n e

The bash exist command:

Now that you know what command exist status codes are, let's look at how to set them using the exit command.

The exit command is used to exit the current shell. It takes a number as a parameter and exits the shell with a status of the number your passed as a parameter value.

If no parameters were supplied, it would return the status of the most recently executed command.

Here is the syntax for the exit command:

$ exit N

When the exit command is used in shell scripts, the value passed to it as an argument is returned to the shell as an exit code.

Here is an example script of using exit command in shell scritps:

Always remember that if a script ends with exit without specifying a parameter, the script exit code is the last command executed in the script.

This is the same as just exit $? or leaving the script without exit at all.


This information should be sufficient to help you understand command exist status codes and the exit command.

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6 Linux bash/zsh history shortcuts that will save you time (every Linux user should know this):

Using bash/zsh history effectively will save you a significant amount of time in the Linux terminal.

This will not only save you time, but it will also make your life much easier when using the LinuxtTerminal to perform day-to-day tasks as a regular user,developer or sysadmin.

Here are 6  Linux bash/zsh history shortcuts that will save you time:

1. Viewing the history

The history bash built-in command is the simplest way to see commands you've used previously.

$ history

This command will display a list of a hundred or thousand commands stored in your history. The size is determined by the $HISTSIZE variable, which can be easily changed if desired.


Simply assign a new value to the variable to change the size, for example, changing the history size to 500 lines run the following command:

$ HISTSIZE=500

If you don't want your screen to be cluttered when viewing your history, you can limit the number of lines to display by using the history command with a numeric argument, where the value is the number of lines to display.

For instance, to display only the last six commands from the history:

$ history 6

This only works in bash; I couldn't find a way to do it in zsh using history options or arguments. Please let me know in the comments if you have.

but you can combine the history command with tail as a workaround:

$ history | tail -n 6


2. Searching commands  from history:

There are two or more methods for searching through the bash history. Personally, I prefer to use the history command in conjunction with the grep command or a convenient shortcut to perform a reverse search through the history.

- Using grep

To search a command from history using grep, run the history command and pipe the output to the command, then specify an expression to search for as a grep option.

$ history | grep "alias"

- Using CTRL + R shortcut

A better and more convenient way to search through history is to use the CTRL + R shortcut key to initiate a reverse search and then type the string you're looking for.

This is a convenient method because it allows us to execute the command once you find it, as opposed to grep, which requires us to retype the command.

For example, searching the 'alias' command:


You can cycle through the options by pressing CTRL + R repeatedly, and once you find the command you want, press CTRL + O or simply the 'enter' key to select and run it. Simply press ESC or CTRL + G to exit the reverse search.

3. Quickly executing commands from history:

Another useful feature of bash/zsh is the ability to run commands from the history using the ! command. That is, you can execute a command by typing !#, where # is the command's position/number in the history.

# can have either a negative or positive value.

$ !364

You can rerun the previous command by using '!!' or '!-1'. This is useful when you forget to run a command with sudo privileges.


You can also run the last command that begins with a specific text, such as this: ! text

Assume you ran echo command before and want to run it again. You can put it to use as follows:

$ !echo


If you have any doubts about a command, rather than running it straight away, print it by appending ':p' to the end of it. So you use it like '!echo:p', '!23:p', and so on.

There is no need to do this if you are using ZSH, as it will display the command before executing it:

4. Correcting typos or mistakes on previous commands:

You can use the ^foor^bar command to edit the command you ran previously and execute it again.

$ sodu mkdir demo
$ ^sodu^sudo

This will replace "sodu" with "sudo" and re-rerun the command.


This is very handy if you want to correct typos or mistakes on long commands.

5. Reuse arguments from previous commands in your history

Another fantastic history shortcut is to use!$ and!*, which will substitute/place the last argument and arguments of the last command into your line, respectively.

Assume you were reading a file with the cat command and decided you needed to edit it with vim or another editor of your choice. You use the '!$' shortcut instead of typing the entire file name.


The above option gives you only the last argument of the previous command. If you want all the arguments, use this the *!


6. Clearing your history

If you feel there are too many commands and you no longer want them, or if you don't want people or other users to know the commands you've been using throughout your session for security reasons, you can simply clear with the option '-c' or -d.



The -c option clears your current history and starts adding commands from scratch, while the -d option deletes the specified command. The -d option only works with BASH, not ZSH.


$ history -c                                       $history -d  380 376


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100+ Linux commands and their explanation (bookmark this):

1. cut - allows you to cut out sections of a specified file or piped data and print the result to standard output.

2. sort - used to sort files

3. uniq - used to extract uniq occurences

4. tr - utility for translating or deleting characters.

5 grep - searches a file for a pattern of characters and displays all lines that match.

6. awk - a scripting language used for text processing.

7. sed - stream editor used to perform lots of functions on files, like searching, find and replace, insertion, or deletion.

8. pstree - used to show running processes in a tree (data structure).

9. latest - displays a list of the most recently logged-in people.

10. w – display a list of the currently logged-in user sessions.

11. free - use to get a detailed report on the system's memory usage.

12. scp - securely copy files or directories over ssh.

13. find - locates files using user-defined criteria.

14. ncdu - provides a useful and convenient way to view disk usage.

15. ip - used to show or manipulate routing, devices, and tunnels.

16. ls - list the contents of a directory.

17. df - Displays the amount of disk space used.

18. du - display a list of all the files along with their respective sizes.

19. diff - used to display differences in files by comparing line by line.

20. uptime – displays the system uptime as well as the load average.

21. top/btop++ – shows a real-time view of running processes in Linux.

22. dstat - allows you to view all of your system resources instantly. All-in-one vmstat, iostat, netstat, and ifstat utility.

 23. Iftop is a network traffic viewer.

24. nethogs - is a network traffic analyzer.

26. vmstat - used to obtain information about memory, system processes, paging, interrupts, block I/O, disk, and CPU scheduling.


27. iotop - is an interactive I/O viewer. Get a snapshot of storage r/w activity.

28. iostat - provides statistics on storage I/O.

29. netstat -used to show network statistics.

30. ss - ss command is a simpler and faster version of the now obsolete netstat command.

31. atop – a tool for monitoring system resources in Linux.

32. ssh – secure protocol used as the primary means of connecting to Linux servers remotely.

33. sudo - run commands with administrative privileges. 34. cd – navigate between directories.

35. touch – used to create, update a computer file or directory's access and modification dates.

36. man – used to read system reference manuals.

37. apropos – searches manual page names and descriptions for a user-supplied keyword.

38. pwd – displays the current directory path.

39. cp - copy files and directories.

40. mv – move file or directories.

41. rm – deletes files and directories.

42. mkdir - create new directories.

43. rsync - remote file transfer and synchronization.

44. tar - is an archive utility.

45. gzip - use for compression and decompression of files.


46. b2zip - a compression utility comparable to gzip. It employs a distinct compression algorithm.

47. zip – used for file packaging and compression (archiving).

 48. locate – in Linux, search for files.

49. ps – allows you to list the status of processes running on your system easily.


50. cron - execute scheduled tasks.

51. mtr - is a network diagnostic tool, a combination of ping and traceroute commands.

52. nslookup - interactively query Internet name servers (NS).

53. host –used for DNS (Domain Name System) lookup operations.

54. dig – DNS lookup tool.

55. nmcli - sused to display network device status, create, edit, activate/deactivate, and delete network connections.

56. ping - sends an ICMP ECHO REQUEST to network hosts. 57. traceroute - examine the path packets follow to reach a specific host.

58. wget - download files through HTTP, HTTPS, FTP, and FTPS.

59. curl – data transport via several network protocols. (Can handle more protocols than wget)

60. dd - used to convert and copy files.

61. fdisk - Modify the disk partition table.

62. parted – used to create and manipulate partition tables.

63. blkid - a command-line utility for finding and printing block device attributes.

64. mkfs - create a Linux file system.

65. fsck - an utility for determining the consistency of a file system.

66. nc - used for just about anything under the sun involving TCP or UDP.

67. umask - returns, or sets, the value of the system's file mode creation mask.

68. chmod – alters the access rights of file system objects.

69. chown – alter the owner and group of a file.

70. chroot - used to change the root directory.

71. useradd - create a new user or alter the default information for a new user.

72. userdel - used to delete a user account and all associated files.

73. usermod – used to edit or change any existing user account's properties.

74. vi is a text editor.

75. cat – displays the contents of a file.

76. tac – reverse output file contents.


77. more - show file contents one screen/page at a time.

78. less – identical to more, but with more features


79. tail – used to show the last few lines of a text file or piped data.

80. head - used to show the first few lines of a text file or piped data.

 81. dmesg – displays the kernel ring's message buffer.

82. journalctl - Tused to view systemd, kernel and journal logs.

83. kill - terminates a process.

84. killall - sends a kill signal to all instances of a specific process.


85. sleep – pauses program execution for a given amount of time.

86. wait – suspend script execution until all background jobs have been completed.


87. nohup - short for no hang up is a command in Linux systems that keep processes running even after exiting the shell or terminal.

88. screen – keep a remote server session open. (It also functions as a full-screen window manager.)

89. tmux is a terminal multiplexer.

90. passwd — Change the password of a user.


91. clear – clears the terminal's screen. 92. env - run a command in an altered environment

91. mount - used to mount the filesystem found on a device to big tree structure(Linux filesystem) rooted at '/'.

92 - umount - unmounts a previously mounted device, directory, file, or file system.

93. systemctl - used to control and manage systemd and services.

94. alias - defines an alias for the specified command.



95. at - runs a specified script or command at a set later time.

96. atq - shows jobs in the at utility queue.

97. atrm - deletes the specified job from the at utility queue.

98. bash - uses the Bourne Again Shell command language to interpret commands from standard input or a file, or to launch a subshell.

99. bc - Performs calculations via its programming language.

100. bash - uses the Bourne Again Shell command language to interpret commands from standard input or a file, or to launch a subshell.


101. bc - Performs calculations via its programming language.

102. chfn - changes the specified user account's current information.


103. chgrp - changes the default group of the specified file or directory.

104. chmod - changes system security permissions for the specified file or directory

105. chown - changes the default owner of the specified file or directory.


106. chpasswd - reads a file of login name and password pairs and updates the passwords.

107. chsh - changes the specified user account's default shell.

108. continue - resumes the next iteration of a for , while , select , or until loop.


109. coproc - spawns a subshell in background mode and executes the designated command or executes a coprocess.

110. env - executes the designated program in a modified environment or displays the value of all the environment variables.

111. htop - a process viewer and manager that is interactive.

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7 command line tools that will change the way you use Linux (instantly) 🧵:

1. tldr

The TLDR (Too Long; Didn't Read) pages provides a summarized practical usage of Linux commands. They simplify man pages by providing practical examples.

This tool is useful when you only want to check the syntax of a few common commands without having to scroll through a detailed manpage.


2. batcat

Did I tell you there is a modern version of cat (batcat) with syntax highlighting for many programming languages out of the box.?🤔


3. exa

exa is a cool replacement for the venerable file-listing command-line program ls that comes with Unix and Linux operating systems, adding features and improving defaults. It uses colors to differentiate between file types and metadata.

It is familiar with symlinks, extended attributes, and Git. It's also small, fast, and only has one binary.

Exa attempts to be a more feature-rich, user-friendly version of ls by deliberately making some decisions differently.


4. btop++

An excellent replacement for top/htop written in C++. Btop++ is a resource monitor that displays statistics and usage information for the processor, memory, disks, network, and processes.


5. duff

If you need a good replacement for the du command, the duff command is your best bet. Duff has the following capabilities:

- Colorful, user-friendly output
- Adapts to the theme and width of your terminal
- Sort the results based on your requirements
- etc


6. zoxide

zoxide is a more intelligent version of the cd command inspired by z and autojump. It remembers which directories you use the most, allowing you to "jump" to them with a few keystrokes. Zoxide is effective on all major shells.

Sounds cool right?


7. lsd

This project is a rewrite of GNU ls with many new features such as colors, icons, a tree-view, more formatting options, and so on. The super colorls project served as a major inspiration for this project.

That concludes today's thread; be sure to experiment with these tools and be amazed. The tools provided above are only the tip of the iceberg.

The more you learn about Linux commands the more straightforward and appealing Linux becomes.

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A complete guide to the du command in Linux 🐧↓

The du command, which stands for "disk usage," returns the estimated amount of disk space used by specified files or directories.

The du command is extremely useful for locating files and directories that are taking up a lot of disk space on your system.

How to Use the du command

The syntax for using this command is as follows:
$ du [OPTION]... [FILE]...

If you provide a FILE as a directory, du will display a summary of disk usage for each file and subdirectory in that directory:

If you don't specify any FILE du will display disk usage of the current working directory.

The du command also allows you to pass multiple files and directories as arguments:

The du command options

The du command has several options that can be used to control how it displays output and what is included in the output.

I'll only go over the most commonly used ones.

The -h option

In most cases, you'd want to show only the amount of space occupied by the specified directory in a human-readable format. To accomplish this, use the -h option.

For instance, to determine the total size of the /home/linuxopsys directory and all of its subdirectories, use the following command:


The -a (--all) option

This useful option does exactly what you'd expect. It displays the sizes of all files, not just directories. For convenience, the -a flag is frequently combined with the -h flag.

Notice, Individual file sizes are listed alongside the directories.


The -s(--summarize) option

The -s option is very important if you only want a summary of the total size of the specified directory, and not for subdirectories.


The -c(--total) option

Another great option is the -c option, this option instructs du to produce a grand total. This is useful when you need to calculate the total size of two or more directories:


--max-depth option

The —max-depth option is useful if you only want to see the disk usage of n-level subdirectories. For example, to obtain a report of the second-level directories, you can use the following command:


That's a warp!

You should now have a better idea of how beneficial the du utility can be. There are numerous flags that I did not cover in this thread, but you can find all of the information on the command's manual page. Simply type 'man du' on terminal to get to the manpage.

End of this thread.

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Linux tip of the day 💡

If you run the program in a terminal, it will be terminated as soon as your terminal session ends. To avoid this and keep the program running, use the nohup command, which stands for "no hangup."

For example, to compress large amount of data using tar command and ensure that the compression continues even if you close the terminal window accidentally, use the following command:

$  nohup tar -cf archive.tar file1 file2


The nohup command also creates a file named nohup.out to store the command's output.

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When managing a multiuser system, you'll frequently need to know who, when, and from where people are logging in.

last is a command-line utility that displays information about system users' most recent login sessions.

It is extremely useful when tracking user activity or investigating a possible security breach.

This thread describes how to use the last command to audit who logged into the system.

[+] Last command usage

The last command has the following syntax:

$ last [options] [username...] [tty...]

When a user logs into the system, a record of that session is added to the /var/log/wtmp file and the last command reads the data in that file to print user login and logouts information.

When last is called without any options or arguments, the output looks like this:

$ last

Each line of output contains the following columns from:

• The first column contains the usernamme. Last shows the special users reboot and shutdown when the system reboots or shuts down.

• The second column is the tty where the session occurred.:0 usually indicates that the user was logging into a desktop environment.

• If there is remote login to the machine last command will show a column which contains the the IP address or the hostname from which the user logged in.

• The session start and stop times.

• The last column shows the session's duration. If the session is still active or the user has not logged out last will diplay "still loggd in", otherwise it will display the duration.

To limit the output to a specific user or tty, use the following command with the user name or tty as an argument:

$ last <username>

You can also specify multiple usernames and ttys as arguments with the last command:

$ last <user1> <user2> <usern>

[+] Last command options

last accepts a number of options for limiting, formatting, and filtering the output. Here , we'll only go over the most common options.

[+] Limiting last output

Last command followed by a single hyphen specifies the number of lines to be printed on the command line. To print only the last 8 login sessions, for example, enter:

$ last -8

[+] Filter ouput by date

You can find out who logged into the system on a specific date by using the -p (--present) option:

$ last -p yyyy-mm-dd

[+] Filter by since and until a specified time

Last can be instructed to display lines since or until a specific time by using the -s (—since) and -t (—until) options.

These two options are frequently used in conjunction to specify a time interval for which the information should be retrieved. For example, to display the login records from 1 December to 3 December, run:

$ last -s 2022-12-01 -u 2022-12-03

[+] Display fulltime

Last does not display the seconds or the year by default. To view full login and logout times and dates, use the -F, --fulltimes option:

$ last -F

[+] Force last to display IP Address and hostnames

The -i (--p) option forces last to always display IP addresses, while the -d (--dns) option displays hostnames:

$ last -i
$ last -d

End of this thread.

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