Users and groups
Linux is a multi-user system.
All users have a unique user id UID (greater than 1000). THis is used to identify them in the system.
Groups:
- are used to organize users and give a shared set of permission and accesses.
/etc/groupshows groups and their members.- Groups also have GID group ids.
Typing id gives information about users and groups they belong to
Current user
To identify who is currently using the terminal, whoami is used.
To see all users currently logged in who or who -a for more details.
Adding and removing Users
Users can be added and deleted in the command line, only by a root user.
To add, sudo useradd benito. This will - create a user - set its home directory in /home/benito - populate it with the files from /etc/skel/ - Set the default shell to bash - All according to /etc/default/useradd
To delete sudo userdel benito - This will leave the home directory (temporal inactivation) - To remove everything userdel -r benito
Modifying Groups
Groups can also be created, modified and removed.
To create a new group use groupadd name.
To delete it groupdel name.
To add an user to an existing group use usermod -aG group_name username - -a Is used to append, and not delete other group memberships - -G is used to list all groups that the user belongs to - Information can be verified with groups username or id username
To delete an user from a group, the usermod command is used in a trick: usermod -G username username makes that the user only has a membership in his default group
Root user
In linux, the root user is also called the superuser.Has access to everything in the system
Is very dangerous and often not justified to grant root access to a user
One can use sudo to execute some tasks with root permissions on a temporary basis - Granted in a peruser basis - Configuration is stored in /etc/sudoers file and /etc/sudoers.d directory - Recommended is to use the visudo tool
Other less recommended option is to use su which allows to substitute another user (in this case the root)