Linux check all existing groups

How to list all groups a user is a member of

Before delving into the 5 ways, let’s first understand some basics:

Adding a user to an existing group is one of the typical tasks of a Linux administrator.

A group is a collection of users. The main purpose of the group is to define a set of privileges to their members within the group.

It can be a difficult task if you want to assign a set of privileges to multiple users without a group. This is where the group comes in handy.

All system users are listed in the /etc/passwd file, the groups are listed in the /etc/group file, and the actual password is stored in the /etc/shadow file.

No matter what command we use, it will fetch information from these files.

There are two types of groups in Linux:

What is primary group?

The primary group is the main group associated with the user account. Each user must be a member of a single primary group.

What is secondary group?

The secondary or supplementary group is used to grant additional rights to the user. Each user can become a member of multiple secondary groups.

What is /etc/passwd file

“/etc/passwd” is a text file containing every user information that is required to login to the Linux system. It maintains useful information about users such as username, password, user ID, group ID, user information, home directory and shell.

Each user profile in the password file is a single line with seven fields as shown below:

$ grep "daygeek" /etc/passwd daygeek:x:1000:1000:daygeek. /home/daygeek:/bin/bash

What is /etc/group file

“/etc/group” is a text file that defines which groups a user belongs to. We can add multiple users in the same group.

Linux has three permission levels which define how users can access it. These levels are user, group and others, which controls a users access to other users’ files and folders.

/etc/group file maintains useful information about the group such as group name, group password, group ID (GIT) and membership list. Each group details is shown in a single line with four fields as shown in the ‘method #5’ listed below.

The following seven commands will help you find out which groups a user belongs to in Linux.

• groups: Show All Members of a Group.
• id: Print user and group information for the specified username.
• lid or libuser-lid: It display user’s groups or group’s users.
• getent: Get entries from Name Service Switch libraries.
• compgen: compgen is bash built-in command and it will show all available commands for the user.
• members: List members of a group.
• /etc/group file: Also, we can grep the corresponding user’s groups from the /etc/group file.

Now let’s delve into the 5 methods which can be used to find the list of groups a user is part of in Linux:

Method-1: Using groups command

The ‘groups’ command is widely used by Linux admin to list all groups a user is a member of. It prints the information of the given user’s primary and supplementary groups as shown below:

$ groups daygeek daygeek : daygeek adm cdrom sudo dip plugdev lpadmin sambashare

Run ‘groups’ command without any arguments to display the list of groups associated with the current user as shown below:

$ groups daygeek adm cdrom sudo dip plugdev lpadmin sambashare

Method-2: Using id command

The id command stands for identity. It prints real and effective user, group, and supplementary group information such as username, UID, group names and GUID as shown below:

$ id daygeek uid=1000(daygeek) gid=1000(daygeek) groups=1000(daygeek),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),118(lpadmin),128(sambashare)

Just run the ‘id’ command to view group information about the current user as shown below:

$ id uid=1000(daygeek) gid=1000(daygeek) groups=1000(daygeek),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),118(lpadmin),128(sambashare)

Method-3: Using lid command

The lid or libuser-lid command displays information about groups containing user name, which requires sudo privileges.

You should run the libuser-lid command instead of the lid on newer systems.

$ sudo libuser-lid daygeek adm(gid=4) cdrom(gid=24) sudo(gid=27) dip(gid=30) plugdev(gid=46) lpadmin(gid=116) daygeek(gid=1000) sambashare(gid=126)

Method-4: Using the getent command

The getent command displays entries from databases supported by the Name Service Switch libraries, which are configured in ‘/etc/nsswitch.conf’:

$ getent group | grep daygeek adm:x:4:syslog,daygeek cdrom:x:24:daygeek sudo:x:27:daygeek,2gadmin dip:x:30:daygeek plugdev:x:46:daygeek lpadmin:x:116:daygeek daygeek:x:1000: sambashare:x:126:daygeek

The above command shows the group name and all other members associated with that group. Use the below customized command format to print only groups for a given user:

$ getent group | grep daygeek | awk -F: '' adm cdrom sudo dip plugdev lpadmin daygeek sambashare

Run the below command to print only the primary group information of the user:

$ getent group daygeek daygeek:x:1000:

Method-5: Using the ‘/etc/group’ file

User groups information can be filtered from the ‘/etc/group’ file using grep command as shown below:

$ grep daygeek /etc/group adm:x:4:syslog,daygeek cdrom:x:24:daygeek sudo:x:27:daygeek,2gadmin dip:x:30:daygeek plugdev:x:46:daygeek lpadmin:x:116:daygeek daygeek:x:1000: sambashare:x:126:daygeek

Use the below customized command format to print only groups for a given user:

$ grep daygeek /etc/group | awk -F: '' adm cdrom sudo dip plugdev lpadmin daygeek sambashare

Bonus Tip-1: Find out all groups using compgen command

Compgen is a bash built-in command that displays all groups in the Linux system:

$ compgen -g root daemon bin sys adm . . daygeek thanu renu sudha admin u1 u2

Bonus Tip-2: Listing members of a group using member command

The member command allows you to list members of a group in Linux:

$ members sudo daygeek 2gadmin

Closing Notes

In this guide, we have shown you several commands to list all groups a user is a member of in Linux.

If you have any questions or feedback, feel free to comment below.

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How to List All Existing Groups in Linux System

Being able to manage users and groups in a Linux operating system environment is an important milestone in terms of Linux administration and security. Under Linux, each user account is automatically associated with a single primary group. A Linux user cannot be a member of two or more primary groups, only one.

However, when it comes to secondary groups, it’s a different case. A single Linux user account can be associated with more than one secondary group (up to 15).

In summary, a primary group is OS-assigned to each Linux user account and is linked to user-created files whereas secondary groups can be associated with multiple Linux user accounts and are not always automatically assigned.

This article will walk us through viable approaches to listing all existing groups within a Linux operating system distribution.

1. Reading the /etc/group File

By default, all defined groups in Linux are listed inside the /etc/group file. The entries in this file are represented in the following format:

group_name:password:GID:group_members

All the password entries are encrypted and GID stands for Group ID.

The entries in the /etc/group file are in plain text making it easier to output its content via a simple cat command.

We can therefore list all groups stored inside the /etc/group file in the following manner:

The above command outputs all groups present in a Linux system as the first column entry followed by the password, GID, and group_members fields if any.

What if we only wanted to output the group_name field? To achieve this objective, we will implement and use the cut command to only extract and output the group_name field from the /etc/group file entries.

• -d tells the cut command to use field delimiters as TABs replacement.
• -f1 tells the cut command to print the content of the first field (field 1) inside the /etc/group file.

2. Using getent Command

As per its manual page, the getent command is effective in accessing Name Service Switch libraries’ entries. The entries in the /etc/group file are supported by databases easily read by the getent command.

The getent command’s reference syntax is as follows:

$ getent [option]. database key.

In our case, its implementation in listing all groups in Linux is straightforward and simple as depicted below:

The first entry in each line represents the group names.

Listing All Groups of a Specific User in Linux

We can now comfortably identify and audit the existence of all groups in our Linux OS environment. What if we wanted to list all groups associated with a particular Linux user?

For the currently logged-in user, all you need to do is execute the following single command:

If you want to audit the groups assigned to other Linux users on the system, reference the following syntax:

For example, we can implement the above command syntax in the following manner:

Have any other ideas on listing all groups in Linux? Feel free to leave a comment or feedback.

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How to check if a group exists and add if it doesn’t in Linux Shell Script

I am using the Ubuntu virtual machine but all of the results i have found on similar sites do not work.

8 Answers 8

The grep statement in the solution of rups has some flaws:

E.g. grepping for a group admin may return true («group exists») when there is a group lpadmin .

Either fix the grep -query

if [ $(getent group admin) ]; then echo "group exists." else echo "group does not exist." fi 

You can chain getent to create the group if it doesn’t exist thusly: getent group admin || groupadd [options] admin You can further chain that with && useradd -G admin someuser to make a one-liner that should create the group if needed and then add the user to it.

The use of getent seems like the most direct answer to the question. It seems to avoid text-parsing corner cases and just returns a 0 or 2 exit code which is what we should be after in a function anyway.

Grepping /etc/group works, but only on a machine where /etc/nsswitch.conf has:

meaning that only /etc/group is consulted when determining available groups. Use either of these (by name or by gid):

getent group getent group

for a more generic solution, checking the exit status: 0 means «exists», non-zero means «does not exist». For example, to check to see if group ‘postgres’ exists, and create it if it does not (assuming bash shell, running as a user able to create new groups) run:

/usr/bin/getent group postgres 2>&1 > /dev/null || /usr/sbin/groupadd postgres 

getent isn’t available on macOS (and possibly all BSD) so it’s not exactly more generic — but it might be ok if you fall back to grep: getent group postgres || grep -q postgres /etc/group

 read -p "enter group name: " group if grep -q $group /etc/group then echo "group exists" else echo "group does not exist" fi 

This is pretty much what i started with that didnt work.. i will attach screenshots of the code and what happens when it runs edit i cant attach pictures edit

I’ve found it more useful, to compose andiba’s solution into a proper function:

This can for e.g be invoked into your environment by including this function in your /etc/bash.bashrc* , such that you can then check for the existence of a group, using the following spell:

Which should then return one of:

group group_name does not exist.

Single line:

Here are 3 commands which should work:

group=sudo grep -qw ^$group /etc/group || groupadd $group usermod -aG $group $USER 

Or one, when you use -f / —force (exit successfully if the group already exists):

groupadd -f mygroup && usermod -aG mygroup $USER 

For completeness, if the group fails to be added, there should be some error handling. E.g., sudo groupadd -f » && echo «success» || echo «fail»

$ groupadd --help Usage: groupadd [options] GROUP Options: -f, --force exit successfully if the group already exists, and cancel -g if the GID is already used 

Geeks great solutions and guidance, thanks for sharing here are my 2 cents to make our lives simpler or lazier 🙂 I could use to complement an useradd script I have to add several users at once. I’m wondering how it would look like inside a for in loop for several groups: group1, group2, group3. group6 Then useradd to the system something like this?

for g in $( cat fewgroups.txt ); do groupadd $g echo «Group:» $g «Exist not added moving on» else echo «Group:» $g «added successfully!» # Then create the users for u in $( cat 100sofusers.txt ); do useradd -m -g group1 -G group2,wheel -d /home/$u -c «Just anothe SiFiGeek» -s /bin/bash $u echo «userID:» $u «added successfully!» echo $u:$randompw | chpasswd echo «Password for userID:» $u «changed successfully» done

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