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Check to see if a script was run as root

Apr 16, 2008  By Mitch Frazier
 in

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
  fi

______________________

Mitch Frazier is an Associate Editor for Linux Journal.

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I don't belive this is the

Anonymous's picture
Submitted by Anonymous (not verified) on Thu, 04/17/2008 - 15:16.

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
fi

hope this help
bye

Not a problem, at least with bash

Mitch Frazier's picture
Submitted by Mitch Frazier on Tue, 04/22/2008 - 11:56.

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
Submitted by lowkey (not verified) on Wed, 04/16/2008 - 13:51.

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.

Maybe

Mitch Frazier's picture
Submitted by Mitch Frazier on Tue, 04/22/2008 - 12:03.

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
Submitted by Anonymous (not verified) on Wed, 04/16/2008 - 20:06.


$ sudo sh -c 'set' | grep UID
SUDO_UID='1000'
$ sudo bash -c 'set' | grep UID
EUID=0
SUDO_UID=1000
UID=0

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
Submitted by charliebrady on Thu, 06/05/2008 - 14:06.

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
Submitted by Mitch Frazier on Tue, 04/22/2008 - 12:12.

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.