usermod (Modify User Account Information)
The usermod (USER MODify) command is used to modify the user profile. The user profile includes Primary Group, Secondary Groups, user ID, user comment, and home directory path, etc.
Check the user status
When you change your user profile, you need to check the status. The /etc/passwd file contains most user profile data but it doesn't include the Secondary Groups that the user belongs to. To have a comprehensive view, you need to run the groups or id command or check the /etc/group file.
1. check user information
There are several ways to check the /etc/passwd file.
grep [user name] /etc/passwdgetent passwd [user name]cat /etc/passwd
As the cat command shows all data contained in the document, the grep or getent commands are more efficient.
For example, to check user_a's user information, you can run one of the commands below.
Or
You'll get the information shown below.
user_a:x:1001:1001::/home/user_a:/bin/sh
This result shows the following
- User ID:
1001 - Primary Group ID:
1001 - User comment: n/a
- Home Directory Path:
/home/user_a - Default Shell:
/bin/sh
2. check group information
There are several ways to check all groups the user is belongs to.
groups [user name]id [user name]- check /etc/group file by the
grep,getentorcatcommand
Running the groups or id command is a quicker way to get the necessary information.
For example, to check user_a's group information, you can run the groups command as shown below.
This result shows that user_a only belongs to its Private Group.
Change User Primary Group (-g option)
To change the user's Primary Group, run the usermod -g [group ID or name] [user name] command as the superuser. For example, to change user_a's primary group to group_a, run the command below.
To check the primary group status, run the command below.
You can see that the Primary Group ID became 1003, which is group_a's group ID.
Add to a Secondary Group (-aG option)
To add a new group, run the command of usermod -aG [group ID or name] [user name] as the superuser. For example, to add a sudo group to user_a's Secondary Group, run the command below.
To check the group status, run the groups command.
You can see that a sudo group is added to user_a's Secondary Group.
IMPORTANT
If you use only the -G option, you'll overwrite the existing group setting. This means that you may mistakenly erase the existing setting and override it. Unless you want to list all groups for the user, use the -aG option.
To list all groups in the -G option, you can connect group names with, (comma) shown below.
By running the groups command, you can see that group_a, group_b, and group_c are added while the sudo group is removed.
user_a : group_a group_b group_c
Change User ID (-u option)
To change the user ID, run the usermod -u [user ID] [user name] command as the superuser. For example, to change user_a's user ID to 2001, run the command below.
To check user_a's user ID, check the /etc/passwd file. You can see that the user ID has changed to 2001.
Change User Comment (-c option)
To change the user comment, run the usermod -c ["Comment"] [User name] command as the superuser. For example, to change user_a's comment to "comment for user_a", run the command below.
To check user_a's user comment, check the /etc/passwd file. You can see that the new comment has been added to the file.
Note: comment is usually used for the user’s full name or other additional information relating to the user.
Change User Home Directory (-d option)
To change the user's home directory, run the usermod -d [directory path] [user name] command as the superuser. For example, to change user_a's home directory to /home/normal_users/user_a, run the command below.
To check user_a's home directory path, switch to user_a and run the cd and pwd command. You can see that the home directory path has changed.
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