GETGROUPS(2) System Calls Manual GETGROUPS(2)

getgroups — get group access list

#include <unistd.h>

int
getgroups(int gidsetsize, gid_t grouplist[]);

() gets the current group access list of the current user process and stores it in the array grouplist[]. The parameter gidsetsize indicates the number of entries that may be placed in grouplist[]. getgroups() returns the actual number of groups returned in grouplist[]. However, no more than {NGROUPS_MAX} will be returned. If gidsetsize is 0, getgroups() returns the number of groups without modifying the grouplist[] array.

Calling initgroups(3) to opt-in for supplementary groups will cause () to return a single entry, the GID that was passed to initgroups(3).

To provide compatibility with applications that use () in environments where users may be in more than {NGROUPS_MAX} groups, a variant of getgroups(), obtained when compiling with either the macros _DARWIN_UNLIMITED_GETGROUPS or _DARWIN_C_SOURCE defined, can be used that is not limited to {NGROUPS_MAX} groups. However, this variant only returns the user's default group access list and not the group list modified by a call to setgroups(2) (either in the current process or an ancestor process). Use of setgroups(2) is highly discouraged, and there is no foolproof way to determine if it has been previously called.

A successful call returns the number of groups in the group set. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error.

The possible errors for getgroups() are:

[]
The argument grouplist specifies an invalid address.
[]
The argument gidsetsize, although non-zero, is smaller than the number of groups in the group set.

#include <sys/param.h> #include <sys/types.h> #include <unistd.h>

The include files <sys/param.h> and <sys/types.h> are necessary.

setgroups(2), initgroups(3), compat(5)

The getgroups() function call appeared in 4.2BSD.

October 28, 2011 BSD 4.2