usermod

Overview

The usermod command modifies user account settings. It allows system administrators to modify various attributes of existing user accounts.

Syntax

usermod [options] LOGIN

Common Options

Option Description
-a, --append Add to supplementary groups
-c, --comment Change comment field
-d, --home Change home directory
-e, --expiredate Set account expiration date
-g, --gid Change primary group
-G, --groups Set supplementary groups
-l, --login Change login name
-L, --lock Lock password
-m, --move-home Move home directory
-s, --shell Change login shell
-U, --unlock Unlock password
-u, --uid Change user ID

Key Use Cases

  1. User management
  2. Access control
  3. Security maintenance
  4. Account modification
  5. Group management

Examples with Explanations

Example 1: Change Shell

usermod -s /bin/bash username

Change user’s login shell

Example 2: Add to Group

usermod -aG sudo username

Add user to sudo group

Example 3: Lock Account

usermod -L username

Lock user account

Understanding Output

  • No output on success
  • Error messages for:
    • Invalid options
    • User not found
    • Permission denied
    • Resource conflicts

Common Usage Patterns

  1. Group management:

    usermod -aG group1,group2 user

  2. Home directory:

    usermod -d /newhome -m user

  3. Account expiry:

    usermod -e 2024-12-31 user

Security Considerations

  1. Password management
  2. Group permissions
  3. Shell restrictions
  4. Account locking
  5. Access control

Additional Resources

Best Practices

  1. Backup before changes
  2. Document modifications
  3. Check permissions
  4. Verify changes
  5. Regular audits

Common Tasks

  1. Group management
  2. Shell changes
  3. Home directory moves
  4. Account locking
  5. Permission updates