id – Print real & effective UIDs and GIDs
Summary :
It prints the user’s info like user id, group id, user name, etc.,
Example:
$ id — Print UID, GID, Groups.
$ id -r — Print only the real user ID.
$ id -u — print only the effective user ID
$ id -nu — Print only user name.
$ id -g — print only the effective group ID.
$ id -ng — Print only group name.
$ id -G — Print all group IDs
$ id -nG — Print all groups name.
$ id user1 — Print info abt user1.
NOTE:
Real UID is the UID of the user, who created. Effective UID is used to evaluate privileges of the process to perform a particular action.
Read : man id