Mastering User Management on Linux

User management is a fundamental skill for Linux administrators. This article covers essential commands for creating, modifying, and deleting user accounts, managing groups, and monitoring user activities in Linux systems.

In the examples below, sai is used as the username for demonstration purposes.

usermod Command

The usermod command modifies existing user account attributes. It allows administrators to change user properties without recreating the account.

To get help information about usermod −

$ usermod --help

Key options include −

-c, --comment COMMENT        new value of the GECOS field
-d, --home HOME_DIR          new home directory for the user account
-e, --expiredate EXPIRE_DATE set account expiration date to EXPIRE_DATE
-f, --inactive INACTIVE      set password inactive after expiration
-g, --gid GROUP              force use GROUP as new primary group
-G, --groups GROUPS          new list of supplementary GROUPS
-a, --append                 append user to supplemental GROUPS
-l, --login NEW_LOGIN        new value of the login name
-L, --lock                   lock the user account
-U, --unlock                 unlock the user account

Basic Usage

$ sudo usermod [options] [username]

Common usermod Operations

Change home directory −

$ sudo usermod --home /home/newpath sai

Set account expiration date −

$ sudo usermod --expiredate 2024-12-31 sai

Lock user account −

$ sudo usermod --lock sai

Unlock user account −

$ sudo usermod --unlock sai

Add user to additional groups −

$ sudo usermod --append --groups wheel,sudo sai

useradd Command

The useradd command creates new user accounts. It is a low-level utility that directly modifies system files like /etc/passwd and /etc/shadow.

To view useradd options −

$ sudo useradd --help

Common options include −

-b, --base-dir BASE_DIR      base directory for the home directory
-c, --comment COMMENT        GECOS field of the new account
-d, --home-dir HOME_DIR      home directory of the new account
-e, --expiredate EXPIRE_DATE expiration date of the new account
-g, --gid GROUP              name or ID of the primary group
-G, --groups GROUPS          list of supplementary groups
-m, --create-home            create the user's home directory
-s, --shell SHELL            login shell of the new account

Basic Usage

$ sudo useradd [options] [username]

Common useradd Operations

Create user with home directory −

$ sudo useradd --create-home --shell /bin/bash sai

Create user with specific home directory −

$ sudo useradd --home-dir /home/custom sai

Create user with expiration date −

$ sudo useradd --expiredate 2024-12-31 sai

Add user to specific groups during creation −

$ sudo useradd --groups wheel,users sai

userdel Command

The userdel command removes user accounts from the system. It can optionally remove the user's home directory and mail spool.

$ userdel --help

Available options −

-f, --force    force removal of files, even if not owned by user
-r, --remove   remove home directory and mail spool
-Z, --selinux-user  remove any SELinux user mapping for the user

Basic Usage

$ sudo userdel [options] [username]

Common userdel Operations

Delete user account only −

$ sudo userdel sai

Delete user with home directory −

$ sudo userdel --remove sai

Force delete user and files −

$ sudo userdel --force sai

Password and Account Management

Change password aging information −

$ sudo chage sai

Interactive output example −

Changing the aging information for sai
Enter the new value, or press ENTER for the default

    Minimum Password Age [0]: 7
    Maximum Password Age [99999]: 90
    Last Password Change (YYYY-MM-DD) [2024-01-15]:
    Password Expiration Warning [7]: 7
    Password Inactive [-1]: -1
    Account Expiration Date (YYYY-MM-DD) [-1]: 2024-12-31

Change user information −

$ sudo chfn sai

Change file ownership −

$ sudo chown sai:sai /path/to/file

Group Management

Command	Purpose	Example
groupadd	Create new group	sudo groupadd developers
groupdel	Delete group	sudo groupdel developers
groups	Show user's groups	groups sai
grpck	Verify group files integrity	sudo grpck

User Monitoring and Information

Display current users and activities −

$ w

Show logged-in users −

$ who

Display current username −

$ whoami

Show user and group IDs −

$ id sai

Example output −

uid=1001(sai) gid=1001(sai) groups=1001(sai),27(sudo),1000(users)

View login history −

$ last

View failed login attempts −

$ sudo lastb

Check login failures by user −

$ sudo faillog -u sai

Conclusion

Effective user management in Linux involves understanding the useradd, usermod, and userdel commands for account lifecycle management, along with group management and monitoring tools. These commands provide comprehensive control over user accounts, permissions, and system security in Linux environments.