INITGROUPS(3)              Library Functions Manual              INITGROUPS(3)

NAME
     initgroups – initialize group access list

LIBRARY
     Standard system libraries.

SYNOPSIS
     #include <unistd.h>

     int
     initgroups(const char *name, int basegid);

DESCRIPTION
     The initgroups() function calculates a group access list for the user
     specified in name.  This group list is then saved in the kernel
     credentials for the current process.  The basegid is included in the
     groups list.  Typically this value is given as the default group
     associated with the user's account record.

     This function sets at most 16 group IDs in the process credentials.  This
     list can be retrieved using the getgroups(2) function.  Note that OS X
     supports group membership in an unlimited number of groups.  The OS X
     kernel uses the group list stored in the process credentials only as an
     initial cache.  Additional group memberships are determined by
     communication between the operating system and the opendirectoryd daemon.

     Processes should not use the group ID numbers from getgroups(2) to
     determine a user's group membership.  The list obtained from getgroups()
     may only be a partial list of a user's group membership.  Membership
     checks should use the mbr_gid_to_uuid(3), mbr_uid_to_uuid(3), and
     mbr_check_membership(3) functions.

RETURN VALUES
     The initgroups() function returns 0 on success.  On failure, this
     function will return -1 and set errno to one of the following values:

     [EPERM]        The caller's effictive UID is not zero.

     [EINVAL]       Internal error, an invalid array size was supplied to the
                    kernel.

     [EFAULT]       Internal error, invalid data was supplied to the kernel.

SEE ALSO
     getgroups(2), getgrouplist(3), mbr_gid_to_uuid(3), mbr_uid_to_uuid(3),
     mbr_check_membership(3).

HISTORY
     The initgroups() function appeared in 4.2BSD.

macOS 15.2                       June 4, 1993                       macOS 15.2