useradd

Overview

The useradd command creates new users or updates default new user information. It is a low-level utility for adding users.

Syntax

useradd [options] login

Common Options

Option Description
-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
-m Create home
-M No home directory
-N No user group
-p password Encrypted password
-r System account
-s shell Login shell
-u uid User ID

Configuration Files

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

Key Use Cases

  1. User creation
  2. Account setup
  3. System accounts
  4. Group management
  5. Security setup

Examples with Explanations

Example 1: Basic User

useradd username

Create basic user

Example 2: Full Setup

useradd -m -G wheel -s /bin/bash username

Create with home and group

Example 3: System User

useradd -r -s /sbin/nologin sysuser

Create system account

Common Usage Patterns

  1. Standard user:

    useradd -m -s /bin/bash user

  2. System account:

    useradd -r service

  3. Group member:

    useradd -G group1,group2 user

Security Considerations

  1. Password policy
  2. Group access
  3. Shell restrictions
  4. Home directory
  5. File permissions

Additional Resources

Best Practices

  1. Strong passwords
  2. Proper groups
  3. Shell security
  4. Directory permissions
  5. Documentation

User Management

  1. Account creation
  2. Group assignment
  3. Home directories
  4. Shell setup
  5. Password policy

Troubleshooting

  1. Permission denied
  2. Group issues
  3. Home directory
  4. Shell problems
  5. Password errors

Common Issues

  1. UID conflicts
  2. Group access
  3. Directory rights
  4. Shell access
  5. Password setup