Zach Sheppard:
> Wietse:
> 
> I have not made any changes to rsyslog.conf. All it does it redirect all
> mail log messages to one log in /var/log/mail which I rotate with a cron
> script nightly. However, I do agree that it really could be the only other
> process that could be hanging the server.
> 
> I'm not able to determine what program is consuming the CPU because I can't
> login to the console when this occurs. The only way I can recover the
> machine is by forcibly powering off.

I suspect that heavy I/O from Postfix and syslog is too much for
your VM.

To diagnose the problem, run screen(1) on a stable machine, and
then open a login session into the VM while it still responsive.
Then come back to that screen session when things go bad. You're
likely to find that when the VM is very slow, all time is spent in
the VM's kernel, and the host's VMM.

Note that VMs, while fine for CPU-bound jobs, can introduce serious
CPU overhead for things that do massive amounts of I/O like Postfix
plus syslog.

If you can't get a better VM, you can reduce the impact from a
'large' mailing by reducing the number of concurrent Postfix SMTP
server and client processes.

# postconf default_process_limit=10 
# postfix reload

        Wietse

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