useradd

Overview

The useradd command creates new user accounts on Linux systems. It sets up the user’s home directory, shell, and initial group memberships according to system defaults or specified parameters.

Syntax

useradd [options] username

Common Options

Option Description
-m Create home directory
-d path Specify home directory path
-s shell Specify login shell
-g group Specify primary group
-G groups Specify supplementary groups
-c comment Add comment/full name
-e date Set account expiry date
-f days Set password expiry
-r Create system account

Key Use Cases

  1. Create new user accounts
  2. Set up system service accounts
  3. Batch user creation
  4. Create users with specific requirements
  5. Set up development environment accounts

Examples with Explanations

Example 1: Create Basic User

useradd -m -s /bin/bash username

Creates user with home directory and bash shell

Example 2: Create System User

useradd -r -s /sbin/nologin systemuser

Creates system user without login ability

Example 3: Create User with Groups

useradd -m -G wheel,developers username

Creates user and adds to specified groups

Understanding Output

  • No output on success
  • Error messages for:
    • Duplicate username
    • Invalid parameters
    • Insufficient permissions
    • Resource constraints

Common Usage Patterns

  1. Create standard user:

    useradd -m -s /bin/bash -c "Full Name" username

  2. Create service account:

    useradd -r -s /sbin/nologin -c "Service Account" svcuser

  3. Create user with specific UID:

    useradd -u 1500 -m username

Performance Analysis

  • Minimal system impact
  • Consider using batch creation for multiple users
  • Use templates (-k) for consistent setup
  • Monitor disk space for home directories

Additional Resources