On Wed, Sep 10, 2014 at 09:55:16AM -0700, Michael Fox wrote:
> Hmmm. O.K. Thanks to both of you. It will take me some time to think this
> through.
>
> The level of indirection between main.cf and master.cf sure adds
> flexibility. But, as someone who doesn't work in postfix every day or even
> every week, it also leaves my head spinning. ;-)
The easiest way to understand this is that main.cf is just a lookup
table that preempts built-in defaults and is loaded at the start
of each Postfix daemon process. This lookup table is in turn
preempted by "-o" command-line switches.
However, both on the command-line and in main.cf itself, parameters
can be recursively defined in terms of other parameters or just
ad-hoc made up "macros".
Since the master.cf file is does not support white-space in argument
values, and is not a good place for maintaining complex parameter
settings, the best practice approach to master.cf overrides is to
define them indirectly in terms of sensibly named "macros" that
are actually defined in main.cf.
main.cf:
some_override =
... too complex to specify directly in master.cf ...
master.cf
service type ... daemon-program
-o some_parameter=$some_override
...
Even if the override value is very simple, it may be better to use
indirection via main.cf, so that someone reading just main.cf can
infer that there are likely master.cf overrides and it may be wise
to look there also.
--
Viktor.
