If you are a Linux system admin who administers Linux servers, you are very frequently asked to create users in Linux unless the organization uses LDAP. As a Linux administrator, you should be well versed with creating and removing users, assigning users to different groups in Linux.
This post explains to you how to create users in Linux using the useradd / adduser command.
Prerequisites
To be able to create a user account, you need to be logged in as a root user or a user with sudo privileges.
useradd command
In Linux, you can create user accounts with useradd / adduser command. The useradd command is a low-level utility which is used for creating user accounts in Linux and other Unix like operating systems.
The adduser command is just a symbolic link to useradd, so it will work similar to useradd command.
Syntax:
useradd [options] user_name
When then the useradd command is issued, the useradd command creates a new user account using options specified by you in the command line and default values specified in /etc/default/useradd file.
Also, the useradd command edits /etc/passwd, /etc/shadow and /etc/group to put an entry of user details and configurations (User and Group IDs, password policies, encryption method), by reading the contents of /etc/login.defs file.
Create a New User in Linux
To create a new user called user_name using the useradd command, run.
useradd user_name
The username must be unique. Otherwise, the system would go through an error that the user name already exists.
Set a password for the newly created account with passwd command to log in to the system with that user.
passwd user_name
You will now be prompted to enter and confirm the password.
Output:
[[email protected] ~]# passwd user_name Changing password for user user_name. New password: Retype new password: passwd: all authentication tokens updated successfully. [[email protected] ~]#
Create a User with Home Directory
As I said earlier, the home directory for a new user may or may not be created when we use the useradd command with no options.
Use the -m option to ensure the home directory for the user is created while creating a new user.
useradd -m user_name
The above command creates the home directory /home/user_name for user user_name and copies files from /etc/skel directory to the user’s home directory.
ls -al /home/user_name
Output:
total 12 drwx------. 2 user_name user_name 62 Apr 15 23:21 . drwxr-xr-x. 4 root root 37 Apr 15 23:21 .. -rw-r--r--. 1 user_name user_name 18 Apr 10 2018 .bash_logout -rw-r--r--. 1 user_name user_name 193 Apr 10 2018 .bash_profile -rw-r--r--. 1 user_name user_name 231 Apr 10 2018 .bashrc
Create a User with Specific Home Directory
When only -m is specified as an option for useradd command, it creates the user’s home directory under /home. If you want to create the user’s home in a different location, use the -d <path_to_homedirectory> along with -m option.
To create a home directory under /opt for user user_name, use.
useradd -m -d /opt/user_name user_name
Create a User with Specific User ID
In Linux, users are identified by UID (Unique Identification Number). By default, whenever the user is created in Linux, the system assigns the next available UID from the range of user IDs between UID_MIN and UID_MAX in the /etc/login.defs file.
Use the -u option to create a user with a specific UID. To create a user called user_name with UID of 9999, you need to use.
useradd -u 9999 user_name
Verify that the user’s UID is 9999 using the id command.
id user_name
Output:
uid=9999(user_name) gid=9999(user_name) groups=9999(user_name)
Create a User with Specific Group
Users are often grouped together with the Linux group. The Linux groups help us to define privileges like read, write or execute to all users within that group for a particular resource. Linux group has its own identification number GID.
When a useradd command is executed without any options, it creates a group with the same as the username and same GID as UID.
Use the -g option to create a user with a specific GID. You can either specify the group name or the GID.
GID
useradd -g 100 user_name
Group Name
useradd -g users user_name
Verify that the user’s GID is 500 using the id command.
id user_name
Output:
uid=1001(user_name) gid=100(users) groups=100(users)
Create a User and Add to Multiple Groups
In Linux, the user can be part of one primary group and multiple secondary groups (optional). The -G option is used to create a user and add to additional groups.
A comma must separate group names.
Syntax:
useradd -G group_name1 group_name2,group_name3 user_name
GID
useradd -G 100,74 user_name
Group Name
useradd -G users,sshd user_name
Verify the groups the user belongs to using the id command.
id user_name
Output:
uid=1001(user_name) gid=1002(user_name) groups=1002(user_name),100(users),74(sshd)
Create a User with an Expiry Date
This option is useful when you want to create a temporary user who will have access to the system only for a period of time. By default, when a useradd command issued without any options, the user will be created with account never expire value.
The -e option allows setting the expiry date for the user. The date must be specified in YYYY-MM-DD format.
To create a new user user_name with an expiry date set to May 1st, 2019, you can use.
useradd -e 2019-05-01 user_name
Verify the user’s expiration date using the chage command.
chage -l user_name
Output:
Last password change : Apr 16, 2019
Password expires : never
Password inactive : never
Account expires : May 01, 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
Create a User with Specific Login Shell
Login shell defines which shell to be invoked when the user logs in. There are lots of login shells are available, such as /bin/bash, /bin/sh, /bin/chsh etc.
By default, when a useradd command issued without any options, the user will be created with /bin/bash (RHEL) or /bin/sh (Debian / Ubuntu) shell.
The -s option allows specifying login shell for the user.
useradd -s /bin/bash user_name
Verify the user’s login shell by reading the /etc/passwd file.
grep -i user_name /etc/passwd
Output:
user_name:x:1001:1002::/home/user_name:/bin/bash
Create a User and Add Comment To User
The -c option allows to add comment in /etc/passwrd for informational purpose.
useradd -c "Demo User" user_name
Check the comment we added for this user.
grep -i user_name /etc/passwd
Output:
user_name:x:1001:1002:Demo User:/home/user_name:/bin/bash
Conclusion
I hope you have learned how to create users in Linux using useradd command. The post explained every single option you can use with the useradd command; however, you can combine options to get the desired results.
Please share your feedback in the comments section.
