groupadd command in Linux with examples

Groups in Linux refer to the user groups. In Linux, there can be many users of a single system, (a normal user can take uid from 1000 to 60000, and one root user (uid 0) and 999 system users (uid 1 to 999)). In a scenario where there are many users, there might be some privileges that some users have and some don’t, and it becomes difficult to manage all the permissions at the individual user level. So, using groups, we can group together a number of users, and set privileges and permissions for the entire group. 

To create a new group, `groupadd` command is used.

Syntax:

groupadd [option] group_name 

Example:  

If we want to create a group named “developers”, we can use the following command.

sudo groupadd developers 

Note: Every new group created is registered in the file “/etc/group“. To verify that the group has been created, enter the command. 

sudo tail /etc/group

sudo tail /etc/group

The file shows group information in the following format:  

group_name : password : group-id : list-of-members

Options Available in `groupadd` command

Options	Description
-f, –force	This option forces the command to silently abort if the group with the given name already exists. If used with the -g or –gid option and the specified group id already exists, the command forcefully ignores the given group id and assigns a new and unique group id.
-g GID, –gid GID	This option assigns a specific numeric group id to the newly created group. The group id (GID) should be non-negative and unique, unless explicitly created to be non-unique using the -o or –non-unique option. If not specified, the command assigns a default group id greater than any existing group id.
-h, –help	Displays a help message, providing information about the groupadd command and its available options. Useful for quickly accessing command documentation.
-K KEY=VALUE, –key KEY=VALUE	Overrides the default values set in the /etc/login.defs file. Multiple -K options can be specified. Parameters like GID_MIN and GID_MAX, defined in /etc/login.defs, can be modified using this option.
-o, –non-unique	Permits adding a group with a non-unique group id (GID). Useful when you want to create groups with duplicate GIDs.
-p PASSWORD, –password PASSWORD	Sets an encrypted password for the group. The password, returned by crypt(3), is visible to users and is stored in the /etc/gshadow file. By default, the password is disabled, and it is crucial to ensure it adheres to the system’s password policy.
-r, –system	Creates a system group. System groups have numeric identifiers chosen within the SYS_GID_MIN-SYS_GID_MAX range, as defined in the /etc/login.defs file, instead of GID_MIN and GID_MAX.
-R CHROOT_DIR, –root CHROOT_DIR	Applies changes in the specified CHROOT_DIR directory and uses the configuration files from that directory. Useful when managing groups within a chroot environment.

Examples

Use of `-f, –force` option in `groupadd` command.

Syntax:

groupadd -f developers

groupadd -f developers

Specifying a Group ID

If we want to assign a specific group id to the newly created group, use the -g option. 

Syntax:

sudo groupadd -g 1001 developers

This command will create a new group named “developer” with a GID of 1001. Specifying group ID is useful in case where we need to maintain consistency across systems.

Setting a Group Password

We can set an encrypted password for a group using the -p option.

Syntax:

sudo groupadd -p somepassword finance

This command creates a new group named “finance” and sets the password for the group as “somepassword”

Overriding Default Values

Suppose we want to modify the GID_MIN and GID_MAX values for a group creation. We can achieve this using the -K option

Syntax:

 groupadd -K GID_MIN=500 -K GID_MAX=700 tester

 groupadd -K GID_MIN=500 -K GID_MAX=700 tester

This command will create a new group named “tester” and set the minimum GID to 500 and the maximum GID to 700. This allows us to have finer control over the range of valid group IDs for the created group.

To add a new user into the group, the group is mentioned using -g option in the command useradd. 

Syntax:

sudo useradd -g developers new_user 

To add an existing user to a group, use the usermod command  

Syntax:

usermod -g developers existing_user  

usermod -g developers existing_user  

Conclusion

In this article we have discussed `groupadd` command. By understanding and utilizing the options we have discussed in the `groupadd` command, we can effectively manage group IDs, create system groups, set group passwords, and customize default value according to our specific requirements and security policies.