Comments on: How to: Check the bash shell script is being run by root or not

By: Erik

Erik — Wed, 03 Aug 2011 19:26:31 +0000

the problem with the last command is that $EUID is evaluated before sudo is executed. To get the effect you are looking for you would need to do something like:

sudo bash -c ‘echo $EUID’

By: Kyle Fuller

Kyle Fuller — Sun, 31 Jul 2011 00:58:10 +0000

A simpler one-liner:
(( EUID )) && echo ‘You need to be root.’ && exit 1

By: @break

@break — Wed, 04 May 2011 07:53:35 +0000

There are differences between shells and sub shells and also when you are running some commands directly in a shell and from a bash script.

By: break

break — Thu, 14 Apr 2011 06:43:02 +0000

Hello Everyone,

Firstly, great blog!

Secondly:

break@breakdown:~$ cat test.sh
#!/bin/bash
echo $EUID
id -u

break@breakdown:~$ ./test.sh
1000
1000
break@breakdown:~$ sudo ./test.sh
0
0
break@breakdown:~$ echo $EUID
1000
break@breakdown:~$ sudo echo $EUID
1000

Vivek can you explain me why last command return my normal-user EUID ? Correct me if I wrong, but “sudo ./test.sh” is executing the same command as last one (“sudo echo $EUID”) so why test.sh is returning root`s EUID ?

OS: Debian Squeeze

By: Andreas

Andreas — Thu, 19 Aug 2010 20:38:19 +0000

Typo @ last example:

echo “You must be a root user” 2>&1
exit 1

has to be

echo “You must be a root user” 1>&2
exit 1

cause you want redirect echo’s stdout to stderr (as it is also done in other examples). :-)

By: jaysunn

jaysunn — Thu, 13 May 2010 15:07:37 +0000

Just used this in one of my scripts.
Thanks Vivek

By: Chris

Chris — Thu, 18 Mar 2010 23:00:22 +0000

Big help, thank you!

By: pierreact

pierreact — Mon, 15 Mar 2010 08:31:43 +0000

An yet another bashism…

By: lorenzo

lorenzo — Tue, 23 Feb 2010 11:58:05 +0000

@hemanth

‘root’ username is not assured. It could be different. id=0 is what is used inside the kernel to identify the superuser (aka root)

By: hemanth

hemanth — Mon, 14 Dec 2009 05:22:16 +0000

I was using this : [[ `id -un` != root ]] && echo You must be root || mount /dev/sdb1 /mnt/disk2

By: gurmad

gurmad — Fri, 27 Nov 2009 01:29:52 +0000

Guys, please help..am a beginner to shell script and lecture gave this assingment:

1 Write a Shell script to automatically check that a specified user is logged in to the
computer.
The program should allow the person running the script to specify the name of the
user to be checked, the frequency in seconds at which the script should check. If a
checking frequency is not specified, it should default to 60 seconds
The script should check for the specified user and if found should output a message
with a “beep” or “bell” sound to the screen stating that the user is logged in. It should
also output a message to a log file stating that the user is logged in and specifying the
date and time.
If the user is not logged in the script should output a message without any “beep”
sound to the screen stating that the user is not logged in.
The script should allow a person running the script to specify the user name on the
command line and optionally, a check frequency in seconds and a third argument “q”
“q” . If “q” is present as a third argument, The script should omit any output to the
screen or “beep” sound but should log to a log file the message stating that the user is
logged in and giving the time.
The command to run the script would be as follows:
checklogin username 30 q where “checklogin” is the script name, “username” is the
name of the user, “30” is the optional frequency to check in seconds, and “q” is the
optional argument to suppress screen output.
The script should check that the number of arguments supplied is between 1 and 3 and
if it is not, should terminate with an error message showing the correct syntax for the
command.
.

By: Laurie

Laurie — Wed, 15 Apr 2009 15:14:42 +0000

@Diana

You need to put your code into the global .bashrc file, /etc/bashrc. This will become the default .bashrc. Beware though, if you make a user specific bashrc then you need to import the global bashrc

By: Arky

Arky — Mon, 09 Mar 2009 07:14:59 +0000

@ terry

The script works as expected.

By: Terry

Terry — Mon, 11 Aug 2008 21:55:32 +0000

I think it’s worth mentioning that $UID & $EUID will not return the desired result if you use sudo to run the script, id -u does however.

By: Fabio

Fabio — Sun, 06 Jan 2008 14:07:05 +0000

Hi,
if you want to redirect a message to stderr using echo you have to use “1>&2″ instead of “2>&1″.
For example,

~ >> f(){
> echo “to stdout” 2>&1
> echo “to stderr” 1>&2
> }
~ >> f 2>/dev/null
to stdout #this is printed to stdout
~ >>

bye

By: diana

diana — Fri, 16 Nov 2007 10:26:08 +0000

may be it was the wrong place to post this.Please help me,
I would like to send mail for each success login.i tried with this,
and place this in /root/.bashrc
#!/bin/bash
echo `last $i | head -1 | awk ‘{print $1″ “$3″ “$4″ “$5″ “$6″ “$7}’`|while read output;
do
echo $output
ip=$(echo $output | awk ‘{print $2}’ )
on=$(echo $output | awk ‘{print $3″ “$4″ “$5}’ )
at=$(echo $output | awk ‘{print $6′} )
echo “User logged in from $ip on $on at $at”|mail -s “Alert: user logged in to server $(hostname) from $ip” ephrondiana@gmail.com
done

but its sending mail for root login only,i need to send mail for users login also.Please help me…

By: vivek

vivek — Mon, 12 Nov 2007 20:37:10 +0000

Nice suggestion, the post has been updated.

By: Jeff Schroeder

Jeff Schroeder — Mon, 12 Nov 2007 18:52:13 +0000

Make error messages go to STDERR (Standard Error) like they do in other Unix programs. That is the best way to do things.

if [ "$(id -u)" != "0" ]; then
echo “This script must be run as root” 2>&1
exit 1
fi