useradd

The Basics of useradd

At its core, useradd creates a new user account. The simplest form is:

sudo useradd username

Replace username with the desired username. This command creates a new user with a home directory in /home/username and a default shell (/bin/bash usually). The sudo prefix is essential, as only the root user or users with sudo privileges can create new accounts.

Let’s create a user named “newuser”:

sudo useradd newuser

Verify the user’s creation:

cat /etc/passwd | grep newuser

This command searches the /etc/passwd file (which contains user account information) for the “newuser” entry.

Specifying the Home Directory

You can specify a custom home directory using the -d or --home-directory option:

sudo useradd -d /home/users/newuser2 newuser2

This creates newuser2 with a home directory located at /home/users/newuser2. Note that the directory must exist before running the command, or you’ll encounter an error. You can create it beforehand using mkdir -p /home/users/newuser2.

Setting the User’s Shell

The default shell is usually Bash (/bin/bash), but you can change it using the -s or --shell option:

sudo useradd -s /bin/zsh newuser3

This creates newuser3 with Zsh as their default shell.

Assigning a User ID (UID) and Group ID (GID)

Each user and group has a unique ID. You can specify these using -u (UID) and -g (GID):

sudo useradd -u 1001 -g 1001 newuser4

This creates newuser4 with UID and GID both set to 1001. Be cautious when manually setting UIDs and GIDs to avoid conflicts.

Creating a User with a Specific Group

You can add the user to a specific group using the -g option:

sudo useradd -g sudoers newuser5

This adds newuser5 to the sudoers group, granting them sudo privileges (assuming sudo is configured correctly). Note that simply adding a user to the sudoers group doesn’t automatically grant sudo privileges; you’ll typically need to edit /etc/sudoers using visudo.

Adding the User to Supplementary Groups

To add a user to multiple groups, use the -G option multiple times or list them comma separated:

sudo useradd -G audio,video newuser6

This adds newuser6 to both the audio and video groups.

Creating a System Account

System accounts are typically used for services and don’t have a home directory. Use the -M option to prevent home directory creation:

sudo useradd -M -s /sbin/nologin systemuser

This creates systemuser without a home directory and with /sbin/nologin as the shell, preventing login.

Using a User Creation Template

You can create a user based on a template account using the -k option:

sudo useradd -k /etc/skel/template newuser7

This will copy the contents of the /etc/skel/template directory (assuming it exists and contains files and settings for new users) to the newuser7’s home directory.

These examples illustrate the power and flexibility of the useradd command. Remember always to use sudo and exercise caution when modifying system settings. Further exploration of the man useradd page is highly recommended for a complete understanding of all available options.