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 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"