vacuum problem

I wonder if vacuum runs as a separate process and where does it have it's
lock file. I'd like to know it because everytime I try to issue a vacuum
command, it says:
elmu=> vacuum analyze ns_log;
ERROR: can't create lock file -- another vacuum cleaner running?

--------------------------------------------------------------------------------
Sebestyén Zoltán <szoli(at)netvisor(dot)hu> I'm believing that the Holy Spirit is
gonna allow the hand, and the foot, and
MAKE INSTALL NOT WAR the mouth, just to begin to speak, and
to minister, and to heal coordinated by
the head.

I use UNIX because reboots are for hardware upgrades.

-- Eagerly waiting for FreeBSD 2.2.8 --