The grp.h header file declares functions used to access group databases.
_POSIX_SOURCE
| getgrgid() | __getgrgid1() | getgrnam() | __getgrnam1() |
_OPEN_SYS
| initgroups() | setgroups() |
_XOPEN_SOURCE_EXTENDED 1
| setgrent() | endgrent() | getgrent() |
_XOPEN_SOURCE 500
| getgrgid_r() | getgrnam_r() |