getgroups(2) -- Linux man page
NAMEgetgroups, setgroups - get/set list of supplementary group IDs
int getgroups(int size, gid_t list);
- Up to size supplementary group IDs are returned in list. It is unspecified whether the effective group ID of the calling process is included in the returned list. (Thus, an application should also call getegid(2) and add or remove the resulting value.) If size is zero, list is not modified, but the total number of supplementary group IDs for the process is returned.
- Sets the supplementary group IDs for the process. Only the super-user may use this function.
- On success, the number of supplementary group IDs is returned. On error, -1 is returned, and errno is set appropriately.
- On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- list has an invalid address.
- For setgroups, the user is not the super-user.
- For setgroups, size is greater than NGROUPS (32 for Linux 2.0.32). For getgroups, size is less than the number of supplementary group IDs, but is not zero.
NOTESA process can have up to at least NGROUPS_MAX supplementary group IDs in addition to the effective group ID. The set of supplementary group IDs is inherited from the parent process and may be changed using setgroups. The maximum number of supplementary group IDs can be found using sysconf(3):
long ngroups_max; ngroups_max = sysconf(_SC_NGROUPS_MAX);The maximal return value of getgroups cannot be larger than one more than the value obtained this way.
CONFORMING TOSVr4, SVID (issue 4 only; these calls were not present in SVr3), X/OPEN, 4.3BSD. The getgroups function is in POSIX.1. Since setgroups requires privilege, it is not covered by POSIX.1.
SEE ALSOinitgroups(3), getgid(2), setgid(2)