Re: [HACKERS] pid file for postmaster?

You are quite correct. They assume that there will be one and only one
postmaster, which may be started or stopped at runlevel switch or
manually via /etc/rc.d/init.d/postmaster stop|start|restart

Similar systems have made PIDfiles like:

/var/run/postgres/5432

Which would get around the single-postmaster limitation and allow you to
make postgres own the PID directory. Whether this has traversal-rights
issues or not, I don't know. Red Hat control starts the postmaster as an
'su' process from root, and they may do the WRITING of the PIDfile from
that account.

Tom Lane wrote:
> 
> Tim Holloway <mtsinc@southeast.net> writes:
> > Red Hat ALREADY creates a file "postmaster.pid" in the /var/lock directory.
> 
> If they did it just like that, then they broke the ability to run more
> than one postmaster on the same machine.  Also, there is the question
> of what the permissions are on /var/lock.  If they're tight then postgres
> can't be an ordinary unprivileged user, which is bad.  If they're loose
> then anyone can come along and cause trouble by fiddling with the lock
> files.
> 
> There was considerable discussion of this whole area last year in
> pg-hackers (check the thread "flock patch breaks things here" and
> related threads starting in late Aug. 1998).  We were focusing mostly
> on the use of lockfiles to ensure that one didn't accidentally start
> two postmasters in the same database dir and/or with the same port
> number; but if the lockfiles contain PIDs then of course they can also
> serve as a contact point for a signal-sender.
> 
> Tatsuo, if you have forgotten that discussion you may want to go back
> and re-read it.
> 
>                         regards, tom lane