could not create semaphores : No space left on device = FreeBSD port install error!

I'm posting this here for search-engine's sake, so future people
having this same problem can find the solution here.

After installing PostgreSQL from FreeBSD's ports, and running su -
pgsql -c initdb for the first time, I got this common error:

could not create semaphores : No space left on device

This page: http://www.postgresql.org/docs/current/static/postmaster-start.html
... and many others tell you to recompile your kernel with different
System V semaphores limits.

I knew this couldn't be it, because I had installed PostgreSQL
successfully on many FreeBSD laptops and desktops.

I tried uninstalling and re-installing. No luck. Same error when
running initdb.

Then I went into "top" and made sure to entirely kill all active
postgresql processes.

Then I ran initdb again and everything was fine.

So --- I think if you install PostgreSQL from FreeBSD ports, and start
the server, and THEN run initdb, it will give you this error.

If you make sure that ALL PostgreSQL processes are stopped (see ps aux
or top) -- then it should work fine.