UNIX / Linux Command To Check Existing Groups and Users

Posted on in Categories , , last updated April 6, 2015

How do I check the existing Linux / UNIX users and groups under Linux operating system?

You can easily check the existing users and groups under a Linux or Unix-like systems such as HP-UX, AIX, FreeBSD, Apple OSX and more using the following commands:

[a] getent command : Fetch details for a particular user or group from a number of important text files called databases on a Linux or Unix-like systems. This is portable and recommended way to get information on users and groups.

[b] Directly query /etc/passwd for user names or /etc/group file for group names.

Method #1: getent command to lookup username and group name

The syntax is as follows to find out if user named foo exists in system:

getent passwd userNameHere
getent passwd foo

The syntax is as follows to find out if group named bar exists in system:

getent group groupNameHere
getent group bar

Sample demo of all commands:

Fig.01: getent and friends demo on a Linux or Unix system to find out user and group names
Fig.01: getent and friends demo on a Linux or Unix system to find out user and group names

Method #2: 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 the following syntax:
grep username /etc/passwd
OR
egrep -i "^username" /etc/passwd
For, example find out if vivek user exists or not, enter:
$ egrep -i "^vivek" /etc/passwd
OR
$ egrep -i "^vivek:" /etc/passwd
Sample outputs:

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.

Use awk command to search user name

The syntax is as follows to search user named ‘apache’

awk -F':' '/^apache/{print $1}' /etc/passwd

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

Say hello to id command

The id command is another option to display user / group information for any USERNAME, or the current user. To find out more about user called, tom, enter:
$ id tom
Sample outputs:

uid=516(tom) gid=516(tom) groups=516(tom)

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:
  • Man pages – id(1),getent(1),passwd(5),group(5)

22 comment

  1. 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

    1. I really wish the author would update the article to include that because you know 7 years later and still no fix? Worse yet, it’s the first Google search result for “linux check if group exists”.

  2. 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.

  3. 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).

  4. 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..

  5. `id` comand does not check if groups exist.
    `man id`

    Print user and group information for the specified USERNAME

    the -g flag prints out the primary group id for the user

  6. Hello
    Linux Gurus,
    Is there a Command to find out user creation date ?

    or any other possible ways to find the same.

    please help me
    Its urgent.

    Thanks In Advance

  7. The grep approaches are all wrong. You are assuming that an user won’t pick a name that is a started substring of an existing group. Even worse, if you choose to limit the ‘username’ string you could match a group instead of a user. You will mistakenly get output from the script thinking that the user ‘apache’ (or whatever) exists…

    You can’t play with strings without semantics. You need a tool that in fact *knows* that what you are talking about is indeed a user.

    The best approach for not playing with strings semantics is the id command:

    NAME
    id – print real and effective user and group IDs

    Regards

  8. As davidhi mentioned
    Using getent is a much better solution in my opinion

    # search for user named ‘vivek’
    getent passwd vivek

    #search for group named ‘vivek’
    getent group vivek

  9. To get the list of all users only shows their usernames
    getent passwd | awk -F: ‘{print $1}’
    To get exact number of user currently logged in
    w | grep “users” | awk -F’ ‘ ‘{print $4}’

    Hope it worked & solve ur issue
    Tested well in centOS 7

    Thanks ,
    SHAHZAD ASLAM

  10. hi,
    I m new to Linux,i want to disable root login..what is the command for that…if I do that will I still be able to login as root…

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