Linux commands you should never run on your system

This article refers to some of the Linux commands you should never run on your system as they might prove to be DEADLY for your Linux systems. So before I proceed, I would like to point out that this article is written for information only to let the readers know that executing any of the following commands are to be avoided. All commands mentioned here can have serious repercussions for your system & its data.

Also Read: Useful Linux Commands that you should know

Recommended Read: Linux Commands for Beginners (Part 1)

So let’s start the list of Linux commands you should never run & might I say again that you proceed with caution,


Linux commands you should never run


1- Format System Disk

Linux Administrator uses this command very often to format and an assign a file system to a newly created disk partition. But when used irresponsibly, this can also format the disk with data on it,

$ mkfs.ext4 /dev/sda

So when using this command, make sure that the intended disk partition has been selected.


2- Delete /etc or /boot directories

/etc holds all the configuration files for the system & /boot holds all kernel, InitRD & GRUB related files, files that are required for system bootup. So delete any of these folders & your system will not boot up,

$ rm -rf /etc

$ rm -rf /boot

Another way to remove configuration files from your system & leave your system to irrecoverable is to use the following command,

$ find / -iname “*.conf” -exec rm -rf {} \;

This will find & remove all the files ending with .conf (configuration files).


3- Delete the entire file system

Most of you might know of this command & it goes like

$ rm -rf /

This will delete the entire file system from your server, deleting every byte of data on disk.


4- Fork Bomb

Now, this command creates copies of itself endlessly & within no time will all your system’s memory, CPU & thus will cause the system crash.

$:(){ :|:& };:

This can also lead to disk corruption.


5- Fill disk with random data

$ dd if=/dev/urandom of=/dev/sda

This will fill the disk with random data. Another variant of this command overwrites the disk several times over the original data,

$ shred /dev/sda

This command is actually a useful tool, especially when you are discarding off the old disk & would not want data from the old disk to fall into wrong hands (& another way I learned from movies is, you can also drill some holes into the drives).


6- File permissions havocs

All the above commands deals with removal or overwriting of data. But there are ways to render your system unusable using the file permissions. First command is ,

$ chmod -Rv 000 /

This command will remove all the file permissions of the all the files or folder on the system & since nobody will have access to files & folders, nobody can access those. & this leads to another way to writing the above command,

$ chown -R nobody:nobody /

This will also accomplish the same output as the first one. Now the second file permission command is actually the opposite of first one,

$ chmod -R 777 /

This will change permissions for all the files & folders to be world writable. & I am sure you can think of what will happen in such a scenario.


So this was our list of Linux commands that you should never run on your system. Please feel free to send in any questions or queries you have regarding this article using the comment box below.

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Shusain

Passionate about Linux & open source. Loves to learn, read & write about Linux as well as new technologies.

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33 Responses

  1. flx says:

    $ chmod -R nobody:nobody /

    should be chown

  2. stakis says:

    blkdiscard is a fast way to destroy a disk

  3. Ray says:

    Dunno if a normal use can execute most of the command’s.
    It should be executed by the root user right ?

  4. Mike says:

    Removing /etc from a stateless SO (solus/clearlinux) will perform a “factory reset”. So it’s a safe operation there.

    • Tushar says:

      $:(){ :|:& };:

      hi shusain and all seniors pls tell us how these regex work in background. really fascinating .

      • Shusain says:

        :() is a function which is called recursively and as you kniw, it can’t be killed since it is running on the background with &. : is actually the name of the function.

        • Rex says:

          Ok so a() { a | a& };a should also work?
          Do we really need the pipe inside the function?
          a() {a&};a would it not work

        • Rock Brentwood says:

          It can be killed by first being put to sleep. The same as in the Star Trek episodes involving Locutus. I *intentionally* did a fork bomb right after those episodes, just to see what would happen.

  5. Leandro Sehnem Heck says:

    These 2 commands should be written in 2 lines

    $ rm -rf /etc $ rm -rf /boot

  6. JSN says:

    Cool… I will try them out and come back later to say what happens in my end… lol

  7. Vivek Kanagaraj says:

    :(){:|:&};: T ## this command is not working. Getting below error

    line 1: syntax error near unexpected token {:’

  8. Shed says:

    Should be rm -rf –no-preserve-root, been like that for decades

  9. Tomas says:

    dd should definitely be on that list, I’ve learned the hard way that it’s very easy to overwrite the wrong partition😬

  10. Parimal says:

    Try # echo > /dev/sda

  11. Jon Smirl says:

    Delete all of you files starting with dot
    rm -rf .*

  12. h1d says:

    # rsync -a –delete ~ root@localhost:/

    Had something similar when a variable positioned before the slash was accidentally empty. (Target machine was obviously a remote one.)

  13. Roger Scumthrope says:

    Probably the quickest way to bring a system down is

    rm -f /lib/{arch_library}/libc-*

    {arch_library} corresponding to i386-linux-gnu, x86_64-linux-gnu etc or may not be necessary at all for some distributions, just depending on where the libc shared object library has been placed.

  14. Simran says:

    Why would anybody goes all the way to type these commands, a sys admin would know what is rm so why would he do that?

  15. Mahendra says:

    Could you please create another blog for all the useful commands in Linux and hp unix

  16. Uwe says:

    On Gentoo it is a lot of fun to remove gcc or tar by “emerge -C gcc” or “emerge -C tar”. After this it is not possible to install or update any package anymore.

  17. my name says:

    Never say never…
    Fork bombs on some systems can cause serious problems, but if your system has a correct setup, then the process limit will prevent crashing the OS.
    If you want to sell your hdd, how can you destroy the content with possibly sensitive data? IMHO you’ll boot a live linux from a USB stick, and dd if=/dev/urandom of=/dev/sda. Isn’t it?

  18. jim says:

    I guess some of these commands are useful, but others like “forkbomb”, I have to ask why the command even exists?

    • Josh says:

      The “forkbomb” presented here is not so much a command that exists. It is just a combination of symbols that are usually used to do useful things.

    • truth says:

      It is not an existing command, it is a definition of a self-replicating function.

  19. stampeder says:

    Using shred on journalled file systems is not as dangerous as some people fear. See the shred man pages.

  20. my name says:

    Forkbombs aren’t existing commands. They are… khm… exploits, AFAIK.
    When I first met with a forkbomb, it was only a silly joke. Today… 🙁
    If your OS isn’t protected against this kind of attacks, then a simple user can crash the whole system (without root/admin privileges).
    But you can protect your linux by setting process limit for all users. (for example, on Ubuntu see the /etc/security/limits.conf or files in limits.d/ folder)
    Please take a look at https://en.wikipedia.org/wiki/Fork_bomb

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