Bash is powerful! Bash is versatile! Bash is amazing!

But all this flexibility & control comes with their own pitfalls. If not used properly, Bash can be devastating as well. At its worst, it can make your entire system unusable too!

⚠︎ Developers must fully understand a command's function before executing it, as ignorance here can prove incredibly costly.

In this blog post, I'm going to discuss several bash commands and patterns that are notoriously popular for causing harm to the systems they run on. Your survival skills must kick in when you encounter any of these.

Fork Bomb

Following mysteriously looking command is known as the Fork Bomb.

:(){ :|:& };:

Never ever make the mistake of running this command to see what it does. (Nor does any other in this post!)

At first glance this command looks odd. Some might even doubt it's validity. It is only after a closer inspection that you will see it invokes a function that recurses without end, and each recursive call spawns a new process. Once executed, processes multiply rapidly, exhausting memory and ultimately crashing the system.

Here is a modified version of the same bash command.

func() {
  func | func &
};
func

See it now? Scary right?

But there is a way to prevent yourself from fork bombs. There is mechanism to limit the number of processes a user can spawn. This can be done by editing the /etc/security/limits.conf.

Disclaimer — I've experienced the havoc of a fork bomb firsthand, and it's certainly humbling (and a bit embarrassing) for any developer.

rm -rf /

Using rm is always a bit dangerous, so developers need to handle it carefully. Picture this: you mean to delete the current folder and its contents with rm -rf ./, but you accidentally type rm -rf /. Notice the missing dot? That tiny mistake tells your computer to start deleting everything — and just like that, your entire system is gone.

You should never run this command — unless you're getting a new machine and completely despise everything on your old one 😉.

A good safeguard to add in your .bashrc is the following.

alias rm='rm -i --preserve-root'

The above alias ensures that the rm command asks for confirmation before deleting anything and ensures that you never delete root by mistake.

If you are interested in many more bashrc tricks, checkout the following article. 👇

Data Eraser

Linux systems offers a command called dd that enables copying data at raw byte level. Operations performed through dd are not reversible and should thus be operated very carefully.

Now look at this command before we start its dissection.

dd if=/dev/zero of=/dev/sda

The if= specifies the source from which bytes should be copies to of=. In Linux, /dev/zero is an infinite source of bytes and /dev/sda is your disk. Thus essentially, this commands overwrites your disk with zeros. 💀

There are no railguards available in the dd command to prevent this from happening accidentally. The best we can do is to disable the dd command if we don't need it.

alias dd='echo "dd command is not available"'

Kill All Processes

The famous kill command is used to stop a running process. While being a handy tool, it should also be used carefully.

Take a look at the following command -

kill -9 -1

The command above sends a SIGKILL to all the processes accessible to the current user. This results in all processes getting killed.

It is thus very important that we never run the kill command with sudo privileges.

chmod -R 777 /

The famous chmod command is used to change the permissions of a file. When used along with its -R flag, the command modifies the permission of files recursively.

Settings permission of a file to 777 essentially means "Permit Everything"!

Similiar to the rm -rf / command, a typo in your chmod command can get you to execute chmod -R 777 / on your machine. Running this command will mess up the permissions on all files present on your machine.

To prevent such unwanted permission modification, you can create an alias in your bashrc that acts as railguard.

alias chmod='chmod --preserve-root'

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Still curious? These are some popular articles of mine that you will enjoy reading! 👇