Since 816614bd62, the service is set to use the exim user so that
systemd takes care of the credentials ownership. The executable is
still required to run as root, to then drop privileges. The prefix '+'
that was used however interfers with the use of privilege restrictions
and other sandboxing options. Since we only want to escape the "User"
setting, we can use the '!' prefix instead.
By settings User= to the actual Exim user, systemd will ensure that the
credentials directory will have the correct ownership, allowing users to
utilize LoadCredential=. Exim still gets started as root (and drops
privileges) to preserve the previous behavior.
the conversion procedure is simple:
- find all things that look like options, ie calls to either `mkOption`
or `lib.mkOption` that take an attrset. remember the attrset as the
option
- for all options, find a `description` attribute who's value is not a
call to `mdDoc` or `lib.mdDoc`
- textually convert the entire value of the attribute to MD with a few
simple regexes (the set from mdize-module.sh)
- if the change produced a change in the manual output, discard
- if the change kept the manual unchanged, add some text to the
description to make sure we've actually found an option. if the
manual changes this time, keep the converted description
this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.
Exim spawns a new queue runner every n minutes as configured by the
argument to -q; up to queue_run_max can be active at the same time.
Spawning a queue runner only every 30 mins means that a message that
failed delivery on the first attempt (e.g. due to greylisting) will only
be retried 30 minutes later.
A queue runner will immediately exit if the queue is empty, so it is
more a function on how quickly Exim will scale to mail load and how
quickly it will retry than something that is taxing on an otherwise
empty system.
This allows the definition of a custom derivation of Exim,
which can be used to enable custom features such as LDAP and PAM support.
The default behaviour remains unchanged (defaulting to pkgs.exim).
