How to check if running as root in a bash script

Question

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 exit

Answer 1

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).