(PHP 5 >= 5.2.0)
posix_initgroups — Calculate the group access list
$name
, int $base_group_id
)Calculates the group access list for the user specified in name.
name
The user to calculate the list for.
base_group_id
Typically the group number from the password file.
成功时返回 TRUE， 或者在失败时返回 FALSE。
victor dot kupiyanov at gmail dot com (2012-03-22 08:19:42)
The function does not calculate groups, it sets groups access list of the current process in accordance to user information in /etc/groups.
Quote from Unix manual page for initgroups:
NAME
initgroups - initialize the supplementary group access list
...
DESCRIPTION
The initgroups() function initializes the group access list by reading the
group database /etc/group and using all groups of which user is a member.
The additional group group is also added to the list.