Linux Pocket Guide, 2nd Edition

Name

id — stdin  stdout  - file  -- opt  --help  --version

Synopsis

id [options] [username]

Every user has a unique, numeric user ID, and a default group with a unique, numeric group ID. The id command prints these values along with their associated user and group names:

$ id
uid=500(smith) gid=500(smith)
groups=500(smith),6(disk),490(src),501(cdwrite)

Useful options

-u	Print the effective user ID and exit.
-g	Print the effective group ID and exit.
-G	Print the IDs of all other groups to which the user belongs.
-n	Print names (for users and groups) rather than numeric IDs. Must be combined with -u, -g, or -G. For example, id -Gn produces the same output as the groups command.
-r	Print login values instead of effective values. Must be combined with -u, -g, or -G.