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.