[systemd-devel] What's the best way to generate .conf files on startup?

[Sean McKay]

Hi all,

I've been looking to dynamically create .conf files at boot depending on
the hardware that I'm running on (to set MemoryMax, if it's relevant). I'd
assumed that the proper way to do this would be by using a generator, since
the .conf file won't automatically be loaded and would require triggering
the system manager to reload all configuration. And it didn't seem prudent
to call that *during* boot.

Then I ran across this little snippet in the man page for
systemd.generator, which seems to imply the opposite:
Generators should only be used to generate unit files and symlinks to them,
not any other kind of configuration. Due to the lifecycle logic mentioned
above, generators are not a good fit to generate dynamic configuration for
other services. If you need to generate dynamic configuration for other
services, do so in normal services you order before the service in question.

What I'm not clear on is whether this refers solely to configuration used
by the daemon itself (to use sshd as a well known example - eg:
/etc/ssh/sshd_config) or if it also refers to drop in .conf files (ie:
something in /run/systemd/system/ssh.service.d/)
Put differently, is a drop in considered to be a unit file or to be
configuration (for the purposes of the above helptext)?

Would the recommended solution in this case be for me to use a generator to
create the relevant .conf file(s) for MemoryMax? Or would it be better to
use a normal service (with proper ordering against the ones it's modifying)
to generate those .conf files and call daemon-reload during boot? If the
latter, are there any expected risks associated with calling daemon-reload
during boot?

Thanks!

-- 
~Sean McKay
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