10 practical examples to use USERADD command in linux

Q: How do you know what default values would be assigned to a user when created using useradd command?

A: These are the two files which contain the default values to be assigned to a user when created using useradd

# less /etc/default/useradd  
 GROUP=100  
 HOME=/home  
 INACTIVE=-1  
 EXPIRE=  
 SHELL=/bin/bash  
 SKEL=/etc/skel  
 CREATE_MAIL_SPOOL=yes

You can also view the default parameters set for new user to be created using

# useradd -D  
 GROUP=100  
 HOME=/home  
 INACTIVE=-1  
 EXPIRE=  
 SHELL=/bin/bash  
 SKEL=/etc/skel  
 CREATE_MAIL_SPOOL=yes

The second file containing values used by useradd command for UID, GID, password encryption method and expiry related information

# less /etc/login.defs  
 MAIL_DIR        /var/spool/mail

 PASS_MAX_DAYS   99999  
 PASS_MIN_DAYS   0  
 PASS_MIN_LEN    5  
 PASS_WARN_AGE   7

 UID_MIN                   500  
 UID_MAX                 60000

 GID_MIN                   500  
 GID_MAX                 60000

 CREATE_HOME     yes  
 UMASK           077

 USERGROUPS_ENAB yes  
 ENCRYPT_METHOD SHA512

1. How to change default values of useradd command?

Either you can open /etc/default/useradd file and edit the file or you can also do the same using CLI as shown below

To change the default home directory location for all new users

# useradd -D -b /opt/users   
# useradd -D | grep HOME  
 HOME=/opt/users

To change the default login shell

# useradd -D -s /bin/sh   
# useradd -D | grep -i shell  
 SHELL=/bin/sh

Now what if you want to add custom arguments to your user while creating them. let us discuss in detail the different options which you can use along with useradd command

2. Create multiple users with same UID

 # useradd -o deepak -u 501  
 # useradd -o deep -u 501  
 # useradd -o user -u 501

Verify the UID of the newly create users

# grep 501 /etc/passwd  
 deepak:x:501:501::/home/deepak:/bin/sh  
 deep:x:501:504::/home/deep:/bin/sh  
 user:x:501:505::/home/user:/bin/sh

3. Manually assign a UID to the user

By default a user automatically gets any free uid more than 500 when you run the useradd command. But what if you manually want to assign a uid to your user

# useradd -u 550 deepak

Let us verify the assigned uid to deepak

# id deepak  
 uid=550(deepak) gid=550(deepak) groups=550(deepak)

4. Create user without home directory

# useradd -M test   
# su - test  
 su: warning: cannot change directory to /home/test: No such file or directory

-bash-4.1$ pwd  
 /root

5. Create user with custom defined home directory

# useradd -d /home/users/test test   
# su - test

$ pwd  
 /home/users/test

6. Add user to different primary group

By default when you run useradd command, a group with the same name is created inside /etc/group but what if you donot want a group to be created with the same name instead add the user to some different already existing group.

Here we will create a user "deep" and add him to group "admin" without creating another "deep" group

# useradd -g admin deep

Verify the groups of user "deep"

# groups deep  
 deep : admin

7. Add user to different secondary group

In the above command you saw if we are mentioning a different primary group while using useradd command then a default group with the name of user is NOT created. Now what if you want a group with username's to be created but instead you want the user to add some secondary group.

Here user deepak is created along with group deepak but also in the same command we are adding deepak to dba group

# useradd  -G dba deepak

Verify groups of deepak

# groups deepak  
 deepak : deepak dba

8. Add user to multiple groups

You can add the user to multiple secondary groups using single command

# useradd -G admin,dba deepak

Verify

# groups deepak  
 deepak : deepak admin dba

9. Manually assign a shell to user

Be default when you create a user in Red Hat Linux the user gets /bin/bash shell. But in case you want to give them some other shell for login use the below command

# useradd -s /bin/sh  deepak   
# su - deepak

-sh-4.1$ echo $SHELL  
 /bin/sh  
 -sh-4.1$

10. Creating a user along with encrypted password

Now you can create a user with pre-defined password, but the condition is the password used should be encrypted which you can do with various methods. Here I will show you one method to do so

Encrypt your password using below command

# [openssl](https://www.golinuxcloud.com/tutorial-pki-certificates-authority-ocsp/) passwd -crypt mypassw0rd  
 Warning: truncating password to 8 characters  
 TuUFdiN1KaCHQ

Now you can use the encrypted password for your new user

# useradd -p TuUFdiN1KaCHQ deepak

Try to login to the user, for which the password would be "mypassw0rd"