Check to see if a script was run as root


If you need to make sure a script is run as root, add the following to the start of the script:

  if [[ $UID -ne 0 ]]; then
    echo "$0 must be run as root"
    exit 1


Mitch Frazier is an Associate Editor for Linux Journal.


Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

I don't belive this is the

Anonymous's picture

I don't belive this is the right way of checking the user. This is as easy as your solution but is harder to bypass.

to bypass your code:

$ sh
$ export UID=0

run command

better way:

LUID=$(id -u)
if [[ $LUID -ne 0 ]]; then
echo "$0 must be run as root"
exit 1

hope this help

Not a problem, at least with bash

Mitch Frazier's picture

Bash won't let you do "export UID=0", UID is a read-only variable.

Mitch Frazier is an Associate Editor for Linux Journal.

Effective User ID

lowkey's picture

You may find it more useful to check for the Effective User ID (EUID) rather than the plain User ID (UID). Then your script will work with SUID cases.

Just replace $UID with $EUID in the above snippet.


Mitch Frazier's picture

As I recall the set-uid bit doesn't work on shell scripts, so unless your script is going to be run by a compiled program that has the set-uid bit set this wouldn't make any difference. Or am I missing something here?

Mitch Frazier is an Associate Editor for Linux Journal.

bash != sh

Anonymous's picture

$ sudo sh -c 'set' | grep UID
$ sudo bash -c 'set' | grep UID

bash provides the environment variable 'UID', but other shells do not. Additionally '[[', while not bash specific is not present in all shells. A better solution (albeit, one dependent on 'id'):

uid=`id -u` && [ "$uid" = "0" ] ||
{ echo "must be root"; exit 1; }

Whose id command?

charliebrady's picture

A little safer/more reliable to do:

uid=$(/usr/bin/id -u) && [ "$uid" = "0" ] ||
{ echo "must be root"; exit 1; }

Use #!/bin/bash

Mitch Frazier's picture

I always put "#!/bin/bash" at the top of my scripts, but beyond that I don't worry about non-bash environments. However, there certainly are some scripts that may run or need to run in an environment where bash does not exist.

Mitch Frazier is an Associate Editor for Linux Journal.

One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix