Linux is a multi-user system which means that more than one person can interact with the same system at the same time. As a system administrator, you have the responsibility to manage the system’s users and groups by creating and removing users and assign them to different groups.
In Linux, you can create a user account and assign the user to different groups using the useradd
command. useradd
is a low-level utility, Debian and Ubuntu users will more likely use the friendlier adduser command instead.
In this article, we will talk about how to use the useradd
command and explore its options.
useradd
Command
The general syntax for the useradd
command is as follows:
useradd [OPTIONS] USERNAME
To be able to use the useradd
command and create new users you need to be logged in as root or a user with sudo access.
When invoked, useradd
creates a new user account using the options specified on the command line plus the default values specified in the /etc/default/useradd
file.
The variables defined in this file differs from distribution to distribution which causes the useradd
command to produce different results on different systems.
The command also reads the content of the /etc/login.defs
file. This file contains configuration for the shadow password suite such as password expiration policy, ranges of user IDs used when creating system and regular users and more.
How to Create a New User in Linux
To create a new user account type useradd
followed by the username.
For example to create a new user named username
you would run:
sudo useradd username
In its simplest form when used without any option, useradd will create a new user account with the default settings specified in the /etc/default/useradd
file.
The command adds an entry to the /etc/passwd
, /etc/shadow,
/etc/group
and /etc/gshadow
files.
To be able to log in as the newly created user, you need to set the user password. To do that run the passwd
command followed by the username:
sudo passwd username
You will be prompted to enter and confirm the password. Make sure you use a strong password.
Changing password for user username.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
How to Add a New User and Create Home Directory
In most Linux distros, when creating a new user account with the useradd
command the user home directory is not created.
Use the -m
(--create-home
) option to create the user home directory as /home/username
:
sudo useradd -m username
The command above creates the new user’s home directory and copies files from /etc/skel
directory to the user’s home directory. If you list the files in the /home/username
directory, you will see the initialization files:
ls -la /home/username/
drwxr-xr-x 2 username username 4096 Dec 11 11:23 .
drwxr-xr-x 4 root root 4096 Dec 11 11:23 ..
-rw-r--r-- 1 username username 220 Apr 4 2018 .bash_logout
-rw-r--r-- 1 username username 3771 Apr 4 2018 .bashrc
-rw-r--r-- 1 username username 807 Apr 4 2018 .profile
Within the home directory, the user can write, edit and delete files and directories.
Creating a User with Specific Home Directory
If you want to create the user’s home directory in other location then the default /home
directory use the d
(--home
) option.
For example, to create a new user named username
with a home directory of /opt/username
you’ll need to run the following command:
sudo useradd -m -d /opt/username username
Creating a User with Specific User ID
In Linux and Unix-like operating systems, users are identified by unique UID and username.
User identifier (UID) is a unique positive integer assigned by the Linux system to each user. The UID along with other access control policies is used to determine the types of actions a user can perform on system resources.
By default when a new user is created the system assigns the next available UID from the range of user IDs specified in the login.defs
file.
Use the -u
(--uid
) option to create a user with a specific UID. For example to create a new user named username
with UID of 1500
you would type:
sudo useradd -u 1500 username
You can verify the user’s UID, using the id
command:
id -u username
1500
Creating a User with Specific Group ID
Linux groups are organization units which are used to organize and administer user accounts in Linux. The main purpose of groups is to define a set of privileges such as reading, writing, or executing permission for a given resource that can be shared among the users within the group.
When creating a new user the default behavior of the useradd
command is to create a group with the same name as the username, and same GID as UID.
Use the -g
(--gid
) option to create a user with a specific initial login group. You can specify either the group name or the GID number. The group name or GID must already exist.
For example to create a new user named username
and set the login group to users
type:
sudo useradd -g users username
To verify the user’s GID, use the id
command:
id -gn username
users
Creating a User and Assign Multiple Groups
There are two types of groups in Linux operating systems Primary group and Secondary or supplementary group. Each user can belong to exactly one primary group and zero or more secondary groups.
The -G
(--groups
) option allows you to specify a list of supplementary groups which the user will be a member of.
The following command will create a new user named username
with primary group users
and secondary groups wheel
and docker
.
sudo useradd -g users -G wheel,developers username
You can check the user groups by typing
id username
uid=1002(username) gid=100(users) groups=100(users),10(wheel),993(docker)
Creating a User with Specific Login Shell
By default, the new user’s login shell is set to the one specified in the /etc/default/useradd
file. In some Linux distributions such as Ubuntu 18.04 the default shell is set to /bin/sh
while in others it is set to /bin/bash
.
The -s
(--shell
) option allows you to specify the new user’s login shell.
For example to create a new user named username
with /usr/bin/zsh
as a login shell type:
sudo useradd -s /usr/bin/zsh username
Check the user entry in the /etc/passwd
file to verify the user’s login shell:
grep username /etc/passwd
username:x :1001:1001::/home/username:/usr/bin/zsh
The -c
(--comment
) option allows you to add a short description for the new user. Typically the user’s full name or the contact information are added as a comment.
In the following example we are creating a new user named username
with text string Test User Account
as a comment:
sudo useradd -c "Test User Account" username
The comment is saved in /etc/passwd
file:
grep username /etc/passwd
username:x :1001:1001:Test User Account:/home/username:/bin/sh
The comment field is also known as GECOS
.
Creating a User with an Expiry Date
The -e
(--expiredate
) option allows you to define a time at which the new user accounts will expire. This option is useful for creating temporary accounts. The date must be specified using the YYYY-MM-DD
format.
For example to create a new user account named username
with expiry time set to January 22 2019 you would run:
sudo useradd -e 2019-01-22 username
You can use the chage
command to verify the user account expiry date:
sudo chage -l username
The output will look something like this:
Last password change : Dec 11, 2018
Password expires : never
Password inactive : never
Account expires : Jan 22, 2019
Minimum number of days between password change : 0
Maximum number of days between password change : 99999
Number of days of warning before password expires : 7
Creating a System User
There is no real technical difference between the system and regular (normal) users. Typically system users are created when installing the OS and new packages.
In some situations, you may need to create a system user that will be used by some application.
Use the -r
(--system
) option to create a system user account. For example, to create a new system user named username
you would run:
sudo useradd -r username
System users are created with no expiry date. Their UIDs are chosen from the range of system user IDs specified in the login.defs
file which is different than the range used for normal users.
Changing the Default useradd Values
The default useradd options can be viewed and changed using the -D
, --defaults
option or by manually editing the values in the /etc/default/useradd
file.
To view the current default options type:
useradd -D
The output will look something like this:
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/sh
SKEL=/etc/skel
CREATE_MAIL_SPOOL=no
Let’s say you want to change the default login shell from /bin/sh
to /bin/bash
. To do that specify the new shell as shown below:
sudo useradd -D -s /bin/bash
You can verify that the default shell value is changed by running the following command:
sudo useradd -D | grep -i shell
SHELL=/bin/bash
Conclusion
In this tutorial, we have shown you how to create new user accounts using the useradd
command. The same instructions apply for any Linux distribution, including Ubuntu, CentOS, RHEL, Debian, Fedora and Arch Linux.
Feel free to leave a comment if you have any questions.