adduser command in Linux

adduser command is used to create a new user in Linux. It is a front-end tool that simplifies the low-level useradd command. It is more user-friendly and interactive. In the backend, it uses a Perl script to provide a nice interactive high-level tool. It uses the configuration information in /etc/adduser.conf to perform actions.

Basic Syntax

adduser [options] username

Common options are:

• -b, --base-dir BASE_DIR: Set default base directory.
• -c, --comment COMMENT: Add user's description (typically full name).
• -d, --home HOME_DIR: Set user's home directory.
• -D: Allows you to view or modify default values used when creating new user accounts. Supported options to use with -D are --base-dir BASE_DIR, ---expiredate EXPIRE_DATE, --inactive INACTIVE, --gid GROUP, --shell SHELL.
• -e, --expiredate EXPIRE_DATE: Set account expiration date.
• -f, --inactive INACTIVE: Set days after password expiry until account disablement.
• -g, --gid GROUP: Set user's primary group.
• -G, --groups GROUP1[,GROUP2,...[,GROUPN]]]: Add user to additional groups.
• -k, --skel SKEL_DIR: Set skeleton directory for user's home.
• -K, --key KEY=VALUE: Override default values.
• -m, --create-home: Create user's home directory.
• -M: Do not create user's home directory.
• -N, --no-user-group: Skip creating group with the same name as user.
• -o, --non-unique: Allow non-unique user IDs.
• -p, --password PASSWORD: Set user's password (not recommended).
• -r, --system: Create a system account.
• -s, --shell SHELL: Set user's login shell.
• -u, --uid UID: Set user's numerical ID.
• -U, --user-group: Create group with the same name as user.
• -Z, --selinux-user SEUSER: Set SELinux user.

Remember some options are specific to Distros. For example -D option is not supported on Debian-based distros.

Using adduser Command

Let's look into some of the most common use cases of the adduser command.

1. Add a new normal user

By default, adduser command adds a normal user to the system. To add a new user simply type adduser followed by the name of the user.

Syntax:

adduser [username]

For example to add a normal user with name bob, type:

sudo adduser bob

adduser command does the following by default when adding a new user:

• Creates a user using the username provided. Choose the first available UID from the range specified in the configuration file.
• Creates a group having the same name as the user. Choose available GID.
• Adds user to the group created.
• Creates a home directory for the user (/home/<username>).
• Starts passwd command to set up the user's password.
• Asks for additional user details.

To add an organizational user account ie system account use --system option. The difference between a normal user is it has no expiry date and uid is below 999.

2. Add a user with a different home directory

By default adduser command creates user's home directory under /home. You can add --home or -d option to create a new user account with a different directory.

Syntax:

adduser [username] --home [directory-path]

For example to create a user named tom with home directory /mnt/data/tom, type:

sudo adduser tom --home /mnt/data/tom

3. Adding a new user to a group

Using adduser command you can easily add an existing user to an existing group.

Syntax:

sudo adduser [existing-username] [exiting-group-name]

For example to add a user named john to the group named developers, type:

sudo adduser tom developers

Make sure the user name and group already exist in the system.

4. Add a User with no password

The adduser with --disabled-login allows to you to add a user with no password. Until the password is set the user won't be able to login.

Syntax:

sudo adduser --disabled-login [username]

For example to add a user named bobs with no password, type:

This command doesn't prompt for a password. Later if you want the user to login, create a password using passwd command.

5. Add a user with disabled password

The adduser command with --disabled-password option allows you to add a user account with no password. But the user can still possible to login the system using SSH keys.

Syntax:

sudo adduser --disabled-password [username]

For example to add a user named john with no password, type:

This is useful when you need a user with only ssh key login for secure authentication.

You can use --gecos option with empty string to avoid asking for finger information such as Full Name, Room Number, Work Phone, Home Phone, and Other. Example:

sudo adduser --disabled-password --gecos "" bob

6. Use a different config file

Instead of using the default configuration file, we can instruct adduser command to use a custom config file. Use adduser command with --conf option for this.

Syntax:

sudo adduser [username] --conf [custom-config.conf]

Example:

sudo adduser thomas --conf custom-config.conf

7. Add a user with a different shell

Instead of the default shell, you can manually specify the users login shell using --shell option. The default shell is specified in the /etc/adduser.conf configuration file - normally /bin/bash or /bin/sh is used.

You can use cat /etc/shells to list all your available shells in your Linux system. From the list choose your desired shell.

For example, to add a user named tomas with login shell zsh, type:

sudo adduser tomas --shell /bin/zsh

You can verify the login shell of the user by listing passwd file as follows:

grep -i tomas /etc/passwd

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About The Author

Bobbin Zachariah

Bobbin Zachariah is an experienced Linux engineer who has been supporting infrastructure for many companies. He specializes in Shell scripting, AWS Cloud, JavaScript, and Nodejs. He has qualified Master’s degree in computer science. He holds Red Hat Certified Engineer (RHCE) certification and RedHat Enable Sysadmin.

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