Summary of 4 ways to add users to groups in Linux

Preface

Linux groups are organizational units used to manage user accounts in Linux. For every user and group in a Linux system, it has a unique digital identification number. It is called User ID (UID) and Group ID (GID). The main purpose of a group is to define a set of privileges for the members of the group. They can all perform specific actions, but not others.

There are two types of default groups in Linux. Each user should have only one primary group and any number of secondary groups.

• Primary Group: When a user account is created, a primary group is added to the user. This is usually the user's name. The primary group is applied to the user while performing any operation like creating a new file (or directory), modifying a file or executing a command. The user's primary group information is stored in the /etc/passwd file.

• Secondary Group: It is called as Secondary Group. It allows a user group to perform specific actions within the same group membership file. For example, it would be ideal if you wanted to allow a few users to run the Apache (httpd) service command.

You may be interested in the following articles related to user management.

• Three ways to create user accounts in Linux?

• How to create batch users in Linux?

• How to update/change user password in Linux using different methods?

This can be achieved using the following four methods.

• usermod: Modifies system account files to reflect changes specified on the command line.

• gpasswd: used to manage /etc/group and /etc/gshadow. Each group can have administrators, members, and passwords.

• Shell Scripts: Allow administrators to automate required tasks.

• Manual way: We can manually add user to any group by editing /etc/group file.

I assume that you already have the required groups and users for this operation. In this example, we will use the following users and groups: user1, user2, user3, and the additional groups are mygroup and mygroup1.

Before making changes, I want to review the user and group information. See below for details.

I can see that the users below are associated with their own group and not with other groups.

# id user1
uid=1008(user1)gid=1008(user1) groups=1008(user1)
 
# id user2
uid=1009(user2)gid=1009(user2) groups=1009(user2)
 
# id user3
uid=1010(user3)gid=1010(user3) groups=1010(user3)

I can see that there are no users associated in this group.

#getent group mygroup
mygroup:x:1012:
 
#getent group mygroup1
mygroup1:x:1013:

Method 1: Using the usermod command

The usermod command modifies system account files to reflect changes specified on the command line.

How to add an existing user to a secondary or additional group using the usermod command?

To add an existing user to a secondary group, use the usermod command with the -g option and the group name.

grammar:

# usermod [-G] [GroupName] [UserName]

If the given user or group does not exist in the system, you will receive an error message. If you don’t get any errors, then the user has been added to the corresponding group.

# usermod -aG mygroup user1

Let me see the output using the id command. Yes, it was added successfully.

# id user1
uid=1008(user1)gid=1008(user1) groups=1008(user1),1012(mygroup)

How to add an existing user to multiple secondary or additional groups using the usermod command?

To add an existing user to multiple secondary groups, use the usermod command with the -G option and the group names separated by commas.

grammar:

# usermod [-G] [GroupName1,GroupName2] [UserName]

In this example, we will add user2 to mygroup and mygroup1.

# usermod -aG mygroup,mygroup1 user2

Let me see the output using the id command. Yes, user2 has been successfully added to myGroup and myGroup1.

# id user2
uid=1009(user2)gid=1009(user2) groups=1009(user2),1012(mygroup),1013(mygroup1)

How to change the primary group of a user?

To change a user's primary group, use the usermod command with the -g option and the group name.

grammar:

# usermod [-g] [GroupName] [UserName]

We have to use -g to change the primary group of the user.

# usermod -g mygroup user3

Let's see the output. Yes, it was changed successfully. Now, the primary group of user3 is shown as mygroup instead of user3.

# id user3
uid=1010(user3)gid=1012(mygroup) groups=1012(mygroup)

Method 2: Using gpasswd Command

The gpasswd command is used to manage /etc/group and /etc/gshadow. Each group can have administrators, members, and passwords.

How to add an existing user to a secondary or additional group using gpasswd command?

To add an existing user to a secondary group, use the gpasswd command with the -M option and the group name.

grammar:

#gpasswd[-M] [UserName] [GroupName]

In this example, we will add user1 to mygroup.

#gpasswd -M user1 mygroup

Let me see the output using the id command. Yes, user1 has been successfully added to mygroup.

# id user1
uid=1008(user1)gid=1008(user1) groups=1008(user1),1012(mygroup)

How to add multiple users to secondary or additional groups using gpasswd command?

To add multiple users to a secondary group, use the gpasswd command with the -M option and the group name.

grammar:

#gpasswd[-M] [UserName1,UserName2] [GroupName]

In this example, we will add user2 and user3 to mygroup1.

#gpasswd -M user2,user3 mygroup1

Let me see the output using the getent command. Yes, user2 and user3 have been successfully added to myGroup1.

#getent group mygroup1
mygroup1:x:1013:user2,user3

How to remove a user from a group using gpasswd command?

To remove a user from a group, use the gpasswd command with the -d option and the name of the user and group.

grammar:

#gpasswd[-d] [UserName] [GroupName]

In this example, we will remove user1 from mygroup.

#gpasswd -d user1 mygroup
Removing user user1from group mygroup

Method 3: Using Shell Script

Based on the above example, I know that the usermod command does not have the ability to add multiple users to a group, which can be done through the gpasswd command. However, it will overwrite existing users currently associated with the group.

For example, user1 is already associated with mygroup. If you were to add user2 and user3 to mygroup using the gpasswd command, it would not work as expected and would instead modify the group.

If I want to add multiple users to multiple groups, what is the solution?

There is no default option in either command to achieve this.

Therefore, we need to write a small shell script to achieve this.

How to add multiple users to a secondary or additional group using gpasswd command?

If you want to add multiple users to secondary or supplementary groups using the gpasswd command, create the following shell script.

Create a user list. Each user should be on a separate row.

$ cat user-lists.txt
user1
user2
user3

Use the following shell script to add multiple users to a single secondary group.

vi group-update.sh
 
#!/bin/bash
for user in `cat user-lists.txt`
do
usermod -aG mygroup $user
done

Set the executable permission for the group-update.sh file.

# chmod +group-update.sh

Finally run the script to implement it.

#sh group-update.sh

Let me see the output using the getent command. Yes, user1, user2, and user3 have been successfully added to mygroup.

#getent group mygroup
mygroup:x:1012:user1,user2,user3

How to add multiple users to multiple secondary or additional groups using gpasswd command?

If you want to add multiple users to multiple secondary or supplementary groups using the gpasswd command, create the following shell script.

Create a user list. Each user should be on a separate row.

$ cat user-lists.txt
user1
user2
user3

Create a group list. Each group should be on a separate row.

$ cat group-lists.txt
mygroup
mygroup1

Use the following shell script to add multiple users to multiple secondary groups.

#!/bin/sh
for user in `more user-lists.txt`
do
for group in `more group-lists.txt`
do
usermod -a -G $group $user
done

Set the executable permission for the group-update-1.sh file.

# chmod +x group-update-1.sh

Finally run the script to implement it.

#sh group-update-1.sh

Let me see the output using the getent command. Yes, user1, user2, and user3 have been successfully added to mygroup.

#getent group mygroup
mygroup:x:1012:user1,user2,user3

Additionally, user1, user2, and user3 are successfully added to mygroup1.

#getent group mygroup1
mygroup1:x:1013:user1,user2,user3

Method 4: Manual method to add user to group in Linux

We can manually add a user to any group by editing the /etc/group file.

Open the /etc/group file and search for the group name of the user you want to update. Finally update the user to the corresponding group.

# vi /etc/group

Summarize

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