freebsd man page for getgroups

GETGROUPS(2)						      BSD System Calls Manual						      GETGROUPS(2)

NAME
     getgroups -- get group access list

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     getgroups(int gidsetlen, gid_t *gidset);

DESCRIPTION
     The getgroups() system call gets the current group access list of the user process and stores it in the array gidset.  The gidsetlen argument
     indicates the number of entries that may be placed in gidset.  The getgroups() system call returns the actual number of groups returned in
     gidset.  At least one and as many as {NGROUPS_MAX}+1 values may be returned.  If gidsetlen is zero, getgroups() returns the number of supple-
     mentary group IDs associated with the calling process without modifying the array pointed to by gidset.

     The value of {NGROUPS_MAX} should be obtained using sysconf(3) to avoid hard-coding it into the executable.

RETURN VALUES
     A successful call returns the number of groups in the group set.  A value of -1 indicates that an error occurred, and the error code is
     stored in the global variable errno.

ERRORS
     The possible errors for getgroups() are:

     [EINVAL]		The argument gidsetlen is smaller than the number of groups in the group set.

     [EFAULT]		The argument gidset specifies an invalid address.

SEE ALSO
     setgroups(2), initgroups(3), sysconf(3)

STANDARDS
     The getgroups() system call conforms to IEEE Std 1003.1-2008 (``POSIX.1'').

HISTORY
     The getgroups() system call appeared in 4.2BSD.

BSD
								 January 21, 2011							       BSD