How to check if running as root in a bash script

I'm writing a script that requires root level permissions, and I want to make it so that if the script is not run as root, it simply echoes "Please run as root." and exits.

Here's some pseudocode for what I'm looking for:

if (whoami != root)
  then echo "Please run as root"

  else (do stuff)
fi

exit

How could I best (cleanly and securely) accomplish this? Thanks!

Ah, just to clarify: the (do stuff) part would involve running commands that in-and-of themselves require root. So running it as a normal user would just come up with an error. This is just meant to cleanly run a script that requires root commands, without using sudo inside the script, I'm just looking for some syntactic sugar.

Solution 1:

The $EUID environment variable holds the current user's UID. Root's UID is 0. Use something like this in your script:

if [ "$EUID" -ne 0 ]
  then echo "Please run as root"
  exit
fi

Note: If you get 2: [: Illegal number: check if you have #!/bin/sh at the top and change it to #!/bin/bash.

Solution 2:

A few answers have been given, but it appears that the best method is to use is:

• id -u
• If run as root, will return an id of 0.

This appears to be more reliable than the other methods, and it seems that it return an id of 0 even if the script is run through sudo.

Solution 3:

In a bash script, you have several ways to check if the running user is root.

As a warning, do not check if a user is root by using the root username. Nothing guarantees that the user with ID 0 is called root. It's a very strong convention that is broadly followed but anybody could rename the superuser another name.

I think the best way when using bash is to use $EUID, from the man page:

EUID   Expands to the effective user ID of the current  user,  initialized
       at shell startup.  This variable is readonly.

This is a better way than $UID which could be changed and not reflect the real user running the script.

if (( $EUID != 0 )); then
    echo "Please run as root"
    exit
fi

A way I approach that kind of problem is by injecting sudo in my commands when not run as root. Here is an example:

SUDO=''
if (( $EUID != 0 )); then
    SUDO='sudo'
fi
$SUDO a_command

This ways my command is run by root when using the superuser or by sudo when run by a regular user.

If your script is always to be run by root, simply set the rights accordingly (0500).

Solution 4:

if [[ $(id -u) -ne 0 ]] ; then echo "Please run as root" ; exit 1 ; fi

or

if [[ `id -u` -ne 0 ]] ; then echo "Please run as root" ; exit 1 ; fi

:)