How do I manage users and groups in Linux?

How do I manage users and groups in Linux? 

These operations are performed using the following commands:
  1. adduser : add a user to the system.
  2. userdel : delete a user account and related files.
  3. addgroup : add a group to the system.
  4. delgroup : remove a group from the system.
  5. usermod : modify a user account.
  6. chage : change user password expiry information.

How do I add a user in Linux? How to Create a New User in Linux. To create a new user account, invoke the useradd command followed by the name of the user. When executed without any option, useradd creates a new user account using the default settings specified in the /etc/default/useradd file.

How do I edit a group in Linux? To modify an existing group in Linux, the groupmod command is used. Using this command you can change the GID of a group, set the group password and change the name of a group. Interestingly enough, you can’t use the groupmod command to add a user to a group. Instead, the usermod command with the -G option is used.

How does groups work in Linux? 

How do groups work on Linux?
  1. Every process belongs to a user (like julia )
  2. When a process tries to read a file owned by a group, Linux a) checks if the user julia can access the file, and b) checks which groups julia belongs to, and whether any of those groups owns & can access that file.