Changing group of php-fpm

Question

I want to execute php-fpm (7.2) with another group while staying in the original groups.

Currently php-fpm runs with www-data as user and group. I've created a new group ( testgrp ) and added the user www-data to the group.

www-data has gid: 33
testgrp has gid: 144

For a spawned PHP-process, /proc/PID/status gives me:

Uid:    33  33  33  33
Gid:    33  33  33  33
Groups: 33 144 

which shows that php runs with www-data as user and main group, but is also in testgrp .

When I set group = testgrp in /etc/php/7.2/fpm/pool.d/www.conf , I get:

Uid:    33  33  33  33
Gid:    144 144 144 144
Groups: 144 

so php runs with testgrp as only group.

Is there a way to change the executing group without loosing the membership of www-data ?

Answer 1

So after looking into the source-code of php-fpm, I found the solution:

I had to add the user www-data to the www-data group (again).
Even though www-data is the primary group of user www-data , it has to be assigned in /etc/group , because php-fpm uses the groups from /etc/group + the provided group while ignoring the primary group.