Ramdisk question

Patrick Ben Koetter p at sys4.de
Sun Mar 21 21:15:50 CET 2021


* Simon Wilson <simon at simonandkate.net>:
> I've configured a 2GB ramdisk and mounted it at /var/spool/amavisd/tmp,
> owned by amavis user. Amavis is using this, I see folders appearing as
> amavisd runs. With a maximum email size of 25M, I'm assuming this is big
> enough, but is there a definitive measure? And will amavisd use it for
> unpacking called scans - e.g. clam?

there is no definite measure. In general the formula would be

    max. message size x max. concurrent amavis processes = max. required space

but there are a few unknown factors to tell if that is sufficient, because

- attachments are usually base64 encoded. When they become base64-decoded and
  written as files to disk, their size *decreases* about by 1/3rd.
- when extracted, file sizes in archives *increase*. How much depends on the
  file type and the packers efficiency that packed file in the first.
- if you have $preserve_evidence enabled amavis will not remove a message and
  all of its parts after a failed scan attempt to allow for inspection. The
  files will remain there until you remove them manually.

Personally I think you are best off, if you double the RAM disk the size of
the formula I mentioned in the first. Enable $preserve_evidence for debugging
purposes only and monitor the RAM discs size and create an alarm if size
shrinks too much.

As for you question regardings "unpacking called scans": Amavis will unpack a
message into a subdirectory of /var/spool/amavisd/tmp. It will create a
separate file for each (MIME) message part contained in the mail message.
Additionally – and only if you've configured amavis to put a copy of the whole
message into the subdirectory using @keep_decoded_original_maps – it will also
put the complete message in there. Only after it has prepared the message for
inspection it will call other scanners, such as clamd, to inspect the message
and its parts.


p at rick

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