Re: systemd controversy

[Alexis <flexibeast@gmail.com>]

Lawrence D'Oliveiro <ldo@nz.invalid> writes:

> systemd service definitions let you state dependencies between services. 
> Furthermore, it separates them into ordering dependencies versus 
> requirement dependencies.
>
> E.g. an application that uses a MariaDB database requires MariaDB to be 
> running before it can be started (ordering + requirement dependency).
>
> An application that can (but doesn’t have to) make use of network services 
> should be started after the network stack is up (ordering dependency).
>
> I’m not aware of any other service-management system that provides this 
> level of control.

s6 supports both dependency management and readiness notification:

  https://skarnet.org/software/s6/overview.html

s6 is the basis for 66, used for service management by Obarun, an
Arch-based distro:

  https://wiki.obarun.org/doku.php?id=66intro

When i was running Void as my daily driver, i was using 66 for service
management. (And not runit, which doesn't have true support for
dependencies; kludges are required.)

The s6 site has a page discussing "socket activation":

  https://skarnet.org/software/s6/socket-activation.html

OpenRC supports integration with s6, and OpenRC itself provides
dependency management; cf. this excerpt from the openrc-run(8) man
page:

> You should define a depend function for the service so that openrc-run
> will start and stop it in the right order in relation to other
> services. As it's a function it can be very flexible, see the example
> below.  Here is a list of the functions you can use in a depend
> function. You simply pass the names of the services you want to add to
> that dependency type to the function, or prefix the names with ! to
> remove them from the dependencies.
>
> need
> The service will attempt to start any services it needs regardless of
> whether they have been added to the runlevel. It will refuse to start
> until all services it needs have started, and it will refuse to stop
> until all services that need it have stopped.
>
> use
> The service will attempt to start any services it uses that have been
> added to the runlevel.
>
> want
> The service will attempt to start any services it wants, regardless of
> whether they have been added to the runlevel.
>
> after
> The service will start after these services and stop before these services.
>
> before
> The service will start before these services and stop
> after these services.
>
> provide
> The service provides this virtual service. For example, named provides
> dns.  Note that it is not legal to have a virtual and real service
> with the same name. If you do this, you will receive an error message,
> and you must rename either the real or virtual service.

There's also dinit, which i don't have any direct experience of; here's
a page by the author, comparing it to other systems:

  https://github.com/davmac314/dinit/blob/master/doc/COMPARISON

(And of course, since cgroups is distinct from systemd, it can be
utilised by any init / supervision / service management system.)


Alexis.