By default, it prints the real user ID, real group ID, effective user
ID if different from the real user ID, effective group ID if different
from the real group ID, and supplemental group IDs. In addition, if
SELinux is enabled and the 'POSIXLY_CORRECT' environment variable is not
set, then print 'context=C', where C is the security context.
groups
列出用户所属的所有组,而不仅仅是所有其他组。来自
man id
: