To know which users exist: cat /etc/passwd | grep -i home
Delete a user: userdel [username]
Add a user: useradd -m [username] (the "-m" flag creates the home directory)
Set the user's password: passwd [username]
Assign a user to a group: usermod -a -G [groupname] [username] (make the user re-login to activate the changes) (for a user to be able to "su" to another one, it has to be in the group "wheel")
View to which groups a user was assigned: groups [username]
Remove a group from a user: usermod -G [all_groups_the_user_is_supposed_to_have-comma_separated] [username] Here I practically reassign to the user only the groups listed and the rest gets deleted. (make the user re-login to activate the changes)
Change the owner of a file: chown [newowner] [filename]
Change the assigned group of a file: chgrp [newgroup] [filename]
Create a group: groupadd [newgroup] Now you can assign files and users to the new group.
