[tor-relays] Changing ulimit for debian-tor

The limit to open files is set to 1024 by default in my system. So it is for the "debian-tor" user, too. It seems to me a bit low. I tried to rise it a whit through "sudo" and getting a shell for debian-tor, but it doesn't work. Can I use PAM-LIMIT with tor ? If not, how can I set ulimit for debian-tor when booting ? And when restarting tor ? BTW, may the open files ulimit preclude a relay to get the "guard" flag ? thanks in advance, Lluís Spain