id — print user identity
id [OPTION...] [USERNAME]
Print information for USERNAME, or the current user.
−aignore, for compatibility with other versions
−Z, −−contextprint only the security context of the current user
−g, −−groupprint only the effective group ID
−G, −−groupsprint all group IDs
−n, −−nameprint a name instead of a number, for −ugG
−r, −−realprint the real ID instead of the effective ID, with
−ugG
−u, −−userprint only the effective user ID
−−helpdisplay this help and exit
−−versionoutput version information and exit
Without any OPTION, print some useful set of identified information.