Error: pid file is invalid, please manually kill the stale server process.

Hi all,

I am using postgres on Ubuntu 12.04 64 bit server. The version is 9.1.10
and I used the stock postgres from Ubuntu repos.

I have a weird problem. Sometimes when the machine is restarted, there
is no $PGDATA/postmaster.pid file. So when I try to restart postgres
(service postgresql restart) I get the following error:

Error: pid file is invalid, please manually kill the stale server process.

An even scarier side-effect of this is that the data, when this happens,
are older than the most recent data in the database.

It may be important to know that postgres runs under monit non sysv init
or upstart.

Also postgres is installed on a customer appliance that may experience
frequent reboots and even abrupt poweroffs! Is postgres in general ideal
for this situation? Is there an optimal configuration for this scenario?

Regards

theo