Support setting supervisor=start-stop-daemon in service files

[meoovv]

...ensuring that it doesnt cause a warning.
closes #1064

[navi-desu]

is there any reason to set supervisor to start-stop-daemon? it's the default (for better or for worse), and well, it's really not a supervisor

removing the warning could be okay, but i don't think it should be documented as a supervisor

[meoovv]

ive described rationale here: #1064 (comment)

permitting start-stop-daemon to be set would be best, i guess, as this would allow explicitly indicating that the service needs s-s-d.

im not sure if its supervisor either 🤔
in my view, parent process is always a supervisor, as its the one who starts and sets process's parameters/permissions.
wikipedia's definition fits well:

A supervisor, or lead, (also known as foreman, boss, overseer, facilitator, monitor, area coordinator, line-manager or sometimes gaffer) is the job title of a lower-level management position and role that is primarily based on authority over workers or a workplace.[

https://en.wikipedia.org/wiki/Supervisor

[navi-desu]

in service managers, supervisor is a software that actively supervises a daemon, with things like auto-restart being expected

start-stop-daemon is more like, an environment setup toolbox and not much more

a service that needs s-s-d is odd though fair, but fwiw end goal is to phase out direct s-s-d usage in favor of supervise-daemon, using things like subreapers on linux to manage double-forking daemons

[meoovv]

end goal is to phase out direct s-s-d

and that would be great! but when will it become a reality? If its likely to happen by the end of next year for example, there might be a reason not to fix the non-critical behavior related to S-S-D and instead move toward marking it as deprecated. but for now, supervise-daemon isn’t even the default, and tbh ive expected it to be by 2024 at least 😅

in service managers, supervisor is a software that actively supervises a daemon, with things like auto-restart being expected

really not sure whether this is a standard definition, rather than just a cognitive distortion shared by many people or maybe a collective image

[meoovv]

not to mention that allowing s-s-d to be set would be the first step toward deprecation!

[navi-desu]

and that would be great! but when will it become a reality? If its likely to happen by the end of next year for example

it really depends on if my life continuing to stabilize, but if so, having all the necessary tools for it end of next year is realistic i think

i'm okay merging the code, but i think docs shouldn't bunch it with the other supervisors, instead, should mention it's an option but also say supervise-daemon is preferred

[meoovv]

done. word "leagcy" could be added, though:
supervisor=start-stop-daemon to use start-stop-daemon
=>
supervisor=start-stop-daemon to use legacy start-stop-daemon

[meoovv]

service-writing guide also needs to be updated to at least mention supervisor option, i guess?

[navi-desu]

service-writing guide needs a full overhaul, and i'm already working on one

it'll become a manpage that'll be installed, plus rendered to html for hosting web docs