[systemd-devel] conditional start with external condition

[Markus Weißmann]

Hello systemd,

I've got an embedded system which can run in two configurations;
configuration 1 will run daemon A, B and C
configuration 2 will run daemon A and D
The configuration is chosen at boot-time with a hardware switch. The 
position of this switch is accessible with a userland tool (via serial 
interface).

I so far came up with two ways of solving this:

1.) start daemon A by default; have the userland tool execute 
"systemctl" to start either B&C or D depending on the position of the 
switch. (Bonus question: Is there a C-API to do that?)
2.) start daemon A by default; have the userland tool execute as a 
one-shot tool that creates files depending on the position of the 
switch. Then have B, C and D depend on the userland tool and use 
ConditionPathExists to only start B&C or D depending on the files 
created by the userland tool.

I'm not totally convinced about either solution, so I'd like an opinion 
on both or perhaps a third solution (perhaps I missed a better 
conditional-option of systemd?)

Bonus question: Will the ConditionPathExists be checked only once and 
if so when exactly? And does this interfere with setting Restart=always? 
(will it be re-evaluated if the daemon needs to be restarted, only once, 
..?)

Thanks a lot!

regards
Markus

-- 
Markus Weissmann, M.Sc.
Technische Universität München
Institut für Informatik
Boltzmannstr. 3
D-85748 Garching
Germany
http://wwwknoll.in.tum.de/