Carlos E. R. wrote:
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The Wednesday 2006-11-15 at 22:08 +0100, Sandy Drobic wrote:
Sigh, I am just typing this the second time due to power outage. Well, at
least I know that my ups is cleanly shutting down all my systems.
...
...
Nice explanation :-)
The first time all my pc were shutting down, I was at work, couldn't
connect to my servers at home anymore and came back to a dark house
without power.
Some workers were busy digging out the earth in the neighbarhood and
destroyed the main power cable for our side of the street. So the ups kept
providing currency for a few minutes, then apcupsd told all server to shut
down. That part worked flawlessly.
After two hours the power returned, they used a temporary workaround, so
people were not left in the dark.
Unfortunately they needed to cut power again to swith back to the repaired
normal power cable, and my ups didn't have to time to recharge
sufficiently, so my workstation was shutting down almost at once again...
I wasn't fast enough to save the draft I was writing on. :-/
One of the things I miss in documentations is an explanation of how things
work, not the usual extensive options explanations, like in
<http://www.postfix.org/documentation.html>. So reading your explanation
is a welcome change.
It's the usual difference between a reference and an in-depth explaining
book designed to teach you WHY things work the way they do.
Though I have to say that Wietse takes great pain to keep the
documentation accurate, up-to-date and even transparent for users of
different versions (most settings available in Postfix have a remark for
which versions of Postfix they have been introduced).
A frequent reply from Wietse is "If it is not documented, it is not
implemented".
A mailinglist server is a special case. If a mailing list has a lot of
subscribers, then a few incoming mails are sufficient to generate many
thousands of outgoing emails.
So Postfix will per default use a max of 100 smtp processes. 5 emails are
submitted to the mailing list manager, 10000 emails are generated, and Postfix
is using all 100 smtp processes to send mails out. If you are using
amavisd-new to first filter the mail, that mail might have to wait for a smtp
process to be free to be delivered to amavisd-new.
Amavis can use "lmtp" instead. But I'm too sleepy to know if it is postfix
to amavis or viceversa O:-)
Bothe amavis and Postfix can use lmtp to transfer mails. The recommended
way though is to define additional transports with the settings you need
for that transport. One example is "relay", another frequently used is
"amavis" or "amavis-smtp". That transport is used to restrict the number
of concurrent processes at a limit the server can handle.
master.cf:
smtp inet n - n - 100 smtpd
-o content_filter=smtp-amavis:[127.0.0.1]:10024
smtp-amavis unix - - n - 2 smtp
-o content_filter=
-o smtpd_recipient_restrictions=permit_mynetworks,reject
-o mynetworks=127.0.0.0/8
That way there are 100 smtpd processes that accept mails but only two smtp
processes are allowed to transfer mails to the expensive content_filter.
If necessary, Mails will pile up in front of the content_filter, but the
server will eventually process them (provided mails don't come in faster
than Amavis can scan them in a reasonable time).
Sandy
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