useradd - Linux

Overview

The useradd command in Linux is used to create new user accounts. It sets up a new user with default settings and configurations based on the system’s user creation policies. This command is essential for systems administrators managing user accounts in multi-user environments or on servers.

Syntax

The basic syntax for useradd is as follows:

useradd [options] USERNAME

Where USERNAME is the name of the new user account to be created.

Options/Flags

Here are some commonly used options and flags for useradd:

  • -d, --home-dir HOME_DIR: Specifies the new user’s login directory.
  • -e, --expiredate EXPIRE_DATE: Sets the date on which the user account will be disabled.
  • -g, --gid GROUP: Specifies the primary group ID or name for the user account.
  • -G, --groups GROUPS: List of supplementary groups for the user.
  • -m, --create-home: Automatically create the user’s home directory if it does not exist.
  • -s, --shell SHELL: Path to the login shell for the user.
  • -u, --uid UID: Set the user’s unique ID. Using this option without specifying a UID will generate an appropriate one automatically.
  • -M: Do not create the user’s home directory, overriding system defaults.
  • -k, --skel SKEL_DIR: When creating a home directory, use files from SKEL_DIR.

The default behavior (if no options are provided) is to create a new user without a home directory, using system defaults for all other parameters.

Examples

  1. Create a new user with default settings: 
    useradd jdoe
  2. Create a new user with a home directory: 
    useradd -m jdoe
  3. Create a new user with a home directory and custom login shell: 
    useradd -m -s /bin/zsh jdoe
  4. Add a new user with a specific UID and multiple supplementary groups: 
    useradd -u 1100 -G staff,developers jdoe

Common Issues

  • Permission Denied: Ensure you have sufficient permissions (usually root) to add a new user.
  • Home Directory already exists: If specifying -m and the home directory exists, the command may fail unless -M is also used.
  • Invalid User ID: Specifying a user ID (-u) that is already taken can result in a conflict. Check existing IDs with id USERNAME.

Integration

useradd can be integrated with other commands for complex scripts. For example, creating a user and setting a password:

useradd newuser && echo "newpassword" | passwd --stdin newuser

This sequence creates a new user and immediately sets a password for them, which can be useful in automated deployment scripts.

  • usermod: Modify a user account.
  • userdel: Delete a user account.
  • passwd: Change user password.
  • groupadd: Add a new group.

For more detailed information or updates on useradd, visit the Linux man page for useradd.