Vacuum problem.

I got this messages while I'm trying to vacuum.

Any idea?

I'm running postgresql-6.3.1 on linux 2.0.27
----------------------------------------------------------------------------
---
bbskorea=> vacuum;
PQexec() -- Request was sent to backend, but backend closed the channel
before r
esponding.
This probably means the backend terminated abnormally before or
while pr
ocessing the request.
bbskorea=> vacuum;
PQexec() -- There is no connection to the backend.
bbskorea=> \q

$ psql bbskorea

bbskorea=> vacuum;
ERROR: can't create lock file -- another vacuum cleaner running?

Do I have to reboot or rerunning postmaster?

Thanks in advance.
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