Dangerous commands you should not try

   I was browsing through Ubuntu forums when I saw this list of dangerous commands. I am copying them for my own reference.  Don't  try them out.

 1)  Delete all files, delete current directory, and delete visible files in current directory.
 

rm -rf /
rm -rf .
rm -rf *

2) Reformat. This command will reformat your hard disk ( you may need superuser permission to run)  

mkfs
mkfs.ext3
mkfs.anything

3) Block device manipulation . These commands manipulate underlying block device. ( here also you may need root permission)

any_command > /dev/sda
dd if=something of=/dev/sda

4) Forkbomb : This will  spawn a number of processes and eventually your system will hang. ( This works for bash shell )

:(){:|:&};: