Display current user and group identity.
# To display current user's ID (UID), group ID (GID) and groups to which they belong:
id
# To display the current user identity:
id -un
# To display the current user identity as a number:
id -u
# To display the current primary group identity:
id -gn
# To display the current primary group identity as a number:
id -g
# To display an arbitrary user's ID (UID), group ID (GID) and groups to which they belong:
id <username>