The initgroups() function reads the group database to get the group membership for the user specified by name, and initializes the supplementary group access list of the calling process (see getgrnam(3C) and getgroups(2)). The basegid group ID is also included in the supplementary group access list. This is typically the real group ID from the user database.

While scanning the group database, if the number of groups, including the basegid entry, exceeds NGROUPS_MAX, subsequent group entries are ignored.

Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.

The initgroups() function will fail and not change the supplementary group access list if:

EPERM

The effective user ID is not super-user.

See attributes(5) for descriptions of the following attributes:

getgroups(2), getgrnam(3C), attributes(5)