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When to use after and requires in systemd?
It is perfectly fine to use both After= and Requires=. They have different purposes. Requires= sets up a start dependency. systemd makes sure that if any body is trying to start foo.service, it should start bar.service too. Should bar.service fails at some point, then foo.service is taken down too. After= is putting a start order between services.
Why does systemd not start foo.service without after =?
If one of the other units fails to activate, and an ordering dependency After= on the failing unit is set, this unit will not be started. Essentially, this means that without After=, both services will be started if foo.service is started (because of Requires= ), but systemd will not stop foo.service if bar.service does not start successfully.
Can you specify more than one requirement in systemd?
This option may be specified more than once or multiple space-separated units may be specified in one option in which case requirement dependencies for all listed names will be created. Note that requirement dependencies do not influence the order in which services are started or stopped.
How to use after stack in Linux systemd?
This directive lists any units upon which this unit essentially depends. If the current unit is activated, the units listed here must successfully activate as well, else this unit will fail. These units are started in parallel with the current unit by default. The units listed in this directive will be started before starting the current unit.
What is the difference between ” wants ” and ” requires ” in systemd?
We have developed a very succinct systemd configuration, and have discovered an obscure nuance between the “wants” and “requires” section options.
What happens when systemd encounters an unknown option?
If systemd encounters an unknown option, it will write a warning log message but continue loading the unit. If an option or section name is prefixed with X-, it is ignored completely by systemd. Options within an ignored section do not need the prefix.
What does the suffix requires mean in systemd?
Similar functionality exists for Requires= type dependencies as well, the directory suffix is .requires/ in this case. This functionality is useful to hook units into the start-up of other units, without having to modify their unit files.