usermod

Overview

The usermod command modifies a user account. It changes various attributes of user accounts including group membership, home directory, and shell.

Syntax

usermod [options] login

Common Options

Option Description
-a Add to groups
-c comment Comment field
-d home_dir Home directory
-e expire_date Account expiry
-f inactive Inactivity period
-g group Primary group
-G groups Secondary groups
-l login_name New username
-L Lock account
-m Move home
-s shell Login shell
-u uid User ID
-U Unlock account

Configuration Files

File Description
/etc/passwd User accounts
/etc/shadow Secure accounts
/etc/group Group accounts
/etc/login.defs System defaults
/etc/skel/ Skeleton files

Key Use Cases

  1. Account modification
  2. Group management
  3. Security control
  4. Shell changes
  5. Directory management

Examples with Explanations

Example 1: Add Group

usermod -aG wheel username

Add to wheel group

Example 2: Change Shell

usermod -s /bin/bash username

Change login shell

Example 3: Lock Account

usermod -L username

Lock user account

Common Usage Patterns

  1. Group addition:

    usermod -aG group user

  2. Home directory:

    usermod -d /new/home -m user

  3. Account lock:

    usermod -L user

Security Considerations

  1. Account access
  2. Group permissions
  3. Shell security
  4. Directory rights
  5. Password policy

Additional Resources

Best Practices

  1. Backup before changes
  2. Check permissions
  3. Verify groups
  4. Document changes
  5. Test access

User Management

  1. Account updates
  2. Group changes
  3. Security controls
  4. Shell management
  5. Directory handling

Troubleshooting

  1. Permission denied
  2. Group issues
  3. Directory problems
  4. Shell errors
  5. Lock/unlock issues

Common Issues

  1. Group conflicts
  2. Home directory
  3. Shell access
  4. Account locks
  5. Permission errors