The getgrouplist function reads through the group file and calculates the group access list for the user specified in name. The basegid is automatically included in the groups list. Typically this value is given as the group number from the password file.
The resulting group list is returned in the array pointed to by groups. The caller specifies the size of the groups array in the integer pointed to by ngroups; the actual number of groups found is returned in ngroups.
The getgrouplist function returns -1 if the size of the group list is too small to hold all the users groups. Here, the group array will be filled with as many groups as will fit.