UNIX / Linux Command To Check Existing Groups and Users
Q. How do I check the existing Linux / UNIX users and groups under Linux operating system?
A. You can easily check the existing users and groups under Linux using the following commands.
Find out if user exists in /etc/passwd file
/etc/passwd file stores essential information required during login. All you have to do is search this file for user name using following syntax:
$ egrep -i "^username" /etc/passwd
For, example find out if vivek user exists or not, enter:
$ egrep -i "^vivek" /etc/passwd
Sample output:
vivek:x:1000:1000:Vivek Gite,,,,:/home/vivek:/bin/bash
A quick shell script code:
#!/bin/bash # init USERID="$1" #.... /bin/egrep -i "^${USERID}" /etc/passwd if [ $? -eq 0 ]; then echo "User $USERID exists in /etc/passwd" else echo "User $USERID does not exists in /etc/passwd" fi # ....
Normally, exit status is 0 returned if user accounts (lines) are found and 1 otherwise.
Find out if group exists in /etc/group file
/etc/group is an text file which defines the groups to which users belong under Linux and UNIX operating system. Again, you have to search /etc/group file using following syntax:
$ egrep -i "^groupname" /etc/group
For, example find out if vivek group exists or not, enter:
$ egrep -i "^vivek" /etc/group
id command
id is another command to display user / group information for any USERNAME, or the current user. To find out more about user called, tom, enter:
$ id tom
Sample output
id: tom: No such user
To find out ftpuser group, enter:
$ id -g ftpuser
Sample output:
id: ftpuser: No such user
id command exit status is 0 returned if user accounts (lines) are found and 1 otherwise. A sample shell script using id command:
#!/bin/bash USERID="$1" /bin/id $USERID 2>/dev/null [ $? -eq 0 ] && echo "User found" || echo "User not found" /bin/id -g $USERID 2>/dev/null [ $? -eq 0 ] && echo "Group found" || echo "Group not found"
Further readings:
- Refer to id, passwd, group man pages
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- FreeBSD add a user to group
- Understanding /etc/group file
- Howto: Linux Add User To Group
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- How can I change the message of the day on my Linux server?
Discussion on This FAQ
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Tags: /etc/group, /etc/passwd, command exit, current user, egrep command, existing users, exit status, grep command, group id, id command, Linux, linux command, UNIX, unix users, user accounts
June 27th, 2008 at 12:15 pm
don’t forget the “:” after the username otherwise you could end up with this scenario:
$ egrep -i “^vivek” /etc/passwd
vivek:x:1000:1000:Vivek Gite,,,,:/home/vivek:/bin/bash
viveks:x:1001:1001:Vivek Smith,,,,:/home/viveks:/bin/bash
June 27th, 2008 at 2:29 pm
If you are using NIS do the following:
ypcat passwd | grep vivek
Ramesh
The Geek Stuff
June 27th, 2008 at 4:00 pm
The ‘id’ command should be demonstrated first in this tutorial, as systems using LDAP (other or remote authentication services) will not have users in the local {passwd,group} files.
Also why the uses of egrep when a simple grep will do. Keep it simple for the beginners your aiming at.
June 27th, 2008 at 6:26 pm
You should look at getent rather than grepping the local files. “getent passwd” or “getent group” will provide a unified view of users or groups available, respecting your NSS (Name Service Switch) configuration (which is important when you have additional users or groups via LDAP or NIS).
August 9th, 2008 at 6:45 pm
hey Vivek, that was cool..
many of us surely wont care if its grep or egrep ( or fgrep) as long as it does the job and we are taught these wonderful tricks..