deadly linux commands #1: Delete Everything

rm -rf /

Explanation : It is a combination of three keywords.
First is : rm – It will remove all the files followed by this
command.
Second is : -rf This will run rm command in more effective
way and will remove everything ( all files and folders
inside the specified folder )without asking confirmation
from the user.
Third is : / – This will start removing the data from the root
directroy and will delete everything from the computer
including the data of removable media.

deadly linux commands #2: Shell function that gets replicated.

Command > :(){ :|: & };:

This command creates a shell function , which once get
initialized starts to create multiple copies of itself.It results
in taking quickly all the memory and power of CPU.It
makes computer freeze or not responding. This is also
known as Denial Of Service Attack.

deadly linux commands #3: format the hard disk.

mkfs.ext4 /dev/sda1

Explanation : This command is again composed of two
keywords.
First is : mkfs.ext4 – This part of command will create a new ext4 file system on following device where this command will get executed.
Second is : /dev/sda1 – This part of command specifies the 1st partition on the first hard disk which is probably in use by the user.
Similarly, This Command:

mkfs.ext3 /dev/sdb2

will Format the second partition on the second hard disk with ext3 File system.

deadly linux commands #4: Writes Any content Directly to a Hard Drive.

 Command > /dev/sda

Explanation : This command will execute normally as other
commands in linux do. But output of this command will
directly be sent to the file system (NTFS or FAT ) of the
Hard Drive. It will result into damaging the file system of
the computer.

deadly linux commands #5: Beware it Will Move your Home Directory To Black hole.

 mv ~ /dev/null

Explanation : Moving any of your content and data to
following path : /dev/null means you want to destroy it.
It means /dev/null is a black hole where once anything
sent , can not be recovered back.
Note:Many of these commands will only be dangerous if
they’re prefixed with sudo on Ubuntu – they won’t work
otherwise. On other Linux distributions, most commands
must be run as root.