How to Create and remove users on ubuntu server 18.04
Creating users in Ubuntu can be done with one of either of two commands: adduser and useradd
Step 1 : First, Creating a User with specific home directory
sudo useradd -d /home/username -m username
Step 2 : If you list the storage of /home, you should see a folder listed there for our new user:
ls -l /home
Step 3 : To create a password for the user, we can use the passwd command.
sudo passwd username
Step 4 : Execute adduser along with a username for a user you wish to create.
sudo adduser username1
I was asked for the password (twice), Full Name, Room Number, Work Phone, Home Phone and Other
Step 5 : To remove a user account, we'll use the userdel command.
sudo userdel username1
The userdel command does not remove the contents of the user's home directory.
Step 6 : We can see that the files for the username1 user still exist
ls -l /home
Step 7 : If you do actually want to remove a user's home directory at the same time you remove an account, just add the -r option
sudo userdel -r username
Understanding the /etc/passwd file
Step 8 : First, let's go over the /etc/passwd file.
Each line within this file corresponds to a user account on the system.
1 : Username
2 : Password (encrypted)
3 : UID (User ID)
4 : GID (Group ID)
5 : User ID Info
6 : Home directory
7 : User's shell
Understanding the /etc/shadow file
Step 9 : Let's take a look at the /etc/shadow file. We can use cat to display the contents
sudo cat /etc/shadow
Step 10: Execute the following command to see the root user account entry in /etc/shadow:
sudo cat /etc/shadow | grep root
Whenever you create a user account on a modern Linux system, the user's password is encrypted (an x is placed in the second column of /etc/passwd for the user), and the actual password hash is stored in the second column of /etc/shadow
Step 10 : The following command will allow you to switch to root from a user account that has sudo access:
sudo su -
Step 11 : Switching to another user account
sudo su - <username>