Disable Ctrl-Alt-Del keyboard shutdown command in GNU/Linux


Don’t think this as a flaw to the GNU/Linux system, but can be helpful in many situations. This part plays a vital role in the security of a system. In GNU/Linux system pressing Ctrl+Alt+Del can cause a shutdwon/reboot by default. As I said this isn’t a bad configuration and most of us may be using this as a shortcut. Moreover it is pretty important if you don’t have the best physical security to the machine. Commenting out the following line/lines will disable the possibility of using the Control-Alt-Delete command to shutdown your computer.

In debian based distros
nano /etc/init/control-alt-delete.conf

   Comment out the lines in the file to look like
   # control-alt-delete – emergency keypress handling
   # This task is run whenever the Control-Alt-Delete key combination is
  # pressed, and performs a safe reboot of the machine.

  description     “emergency keypress handling”
  #author         “Scott James Remnant <scott@netsplit.com>”

  #start on control-alt-delete

  #exec shutdown -r now “Control-Alt-Delete pressed”

In redhat based distros
nano /etc/inittab

Comment the following line

    ca::ctrlaltdel:/sbin/shutdown -t3 -r now

to look like

    #ca::ctrlaltdel:/sbin/shutdown -t3 -r now
Save the file and logout.

chattr command for setting a file immutable

Usually chattr is used for changing the file attributes on Linux file system. It is different from chmod command. Any file’s permission set by chmod command can be bypassed with the root privilege. Whereas if a file is set immutable by the chattr command it cannot be modified even with super user privilege. Afterall chattr command can be used only with super user privilege. Even though it is more efficient than chmod.

To set a file immutable run
chattr +i file
with super user privilege.