[systemd-devel] I want to ask you a fundamental question to you about dependency and starting sequence among units.

[Tony Seo]

 Hello.

 As I'm a starter in systemd, I want to ask you a fundamental question.

 That is how to understand existing relation from dependent and starting
perspective.

 If you check a image file I attached, it' more clear.

 Actually, I have studied systemd structure to add my processes in systemd
structure.

 Although I have read many manpage whicn is on freedesktop.org,  I thought
that I might not yet understand dependency and boot sequence among units
after comparing results from systemd-analyze plot and dot tool.

 So, I want to get clear conception of dependency and boot sequence.





 When I first read a manpage which explains [Unit] option, I find a
"Wants=".

 For example, I make a "A.service" which has an "Want = B.service".

 If A.service is started by systemd, I think that B.service will be started
after A.service is totally completed.
( Is it right to use a words "totally completed to explain execution of
A.sevice?
  And I'm confused words which explain some parts of "Wants=", I couldn't
understand the expression "start-up".
 Does it mean that a unit listed in "Want=" option will be started after
the configuring unit is finished? )

 if so, I think this relationship like below

1. B.service is a dependency of A.service.
2. A.service is started before B.service is started in sequential
perspective of boot sequence among units.
3. if B.service is in A.service.want folder, a implicit dependency is made
between A.service and B.service( result will be same as No.1)


In my view, this is a critical time to develop the knowledge of systemd.

I wait someone who explains those things more definite than before.

Thanks


Tony Seo
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