I'm trying to send input to a screen session from php. So far I have followed the steps explained here
Is running GNU Screen suid root the only way to make multiuser mode work?

And I have set "multiuser on" and "acladd www-data" in the screenrc file (or well, no. in another file that I use by the -c option but still)

My problem now is that whenever i try to acess screen by php

exec('screen -S user/session -p 0 -X stuff "test"'."\n", $ret);  

I get the error:

Cannot opendir /var/run/screen/S-user: Permission denied