`useradd`

The useradd command (often symlinked or aliased to adduser in some distributions) is a low-level utility used to create a new user account on a Linux system. It modifies system files like /etc/passwd, /etc/shadow, and /etc/group, and optionally creates a home directory for the user.

Note: You typically need root or sudo privileges to run this command.

Basic Syntax

useradd [OPTIONS] USERNAME

Common Flags/Options

Option	Description
`-m`, `--create-home`	Create the user's home directory.
`-d`, `--home-dir HOME_DIR`	Specify a custom home directory path.
`-s`, `--shell SHELL`	Specify the user's login shell (e.g., `/bin/bash`).
`-g`, `--gid GROUP`	Specify the name or ID of the user's primary group.
`-G`, `--groups GROUPS`	Specify a comma-separated list of supplementary groups.
`-e`, `--expiredate EXPIRE_DATE`	Set the date on which the user account will be disabled (Format: YYYY-MM-DD).

Real-world Examples

1. Create a basic user with a home directory

By default, useradd might not create a home directory depending on the Linux distribution's configuration. Use -m to ensure it is created.

sudo useradd -m alice

2. Create a user with a specific shell and supplementary groups

Create a developer user who needs a bash shell and access to the docker and sudo groups.

sudo useradd -m -s /bin/bash -G docker,sudo bob

3. Create a temporary user with an expiration date

Useful for contractors or temporary access.

sudo useradd -m -e 2024-12-31 tempuser

System users are typically used for running services and do not need a login shell or home directory.

sudo useradd -r -s /usr/sbin/nologin nginx_worker

(The -r flag indicates a system account, assigning a UID below 1000).

Basic Syntax​

Common Flags/Options​

Real-world Examples​

1. Create a basic user with a home directory​

2. Create a user with a specific shell and supplementary groups​

3. Create a temporary user with an expiration date​

4. Create a system user (no login)​