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Re: Systemd dependencies




Am 26.02.2018 um 10:29 schrieb Bastian Blank:
> Hi Michael
> 
> On Mon, Feb 26, 2018 at 09:46:22AM +0100, Michael Meskes wrote:
>> do we have something like virtual entities for systemd service files? In SysV
>> we could require that mail-transport-agent was started before starting a
>> service. But how is this supposed to be handled with systemd?
> 
> You can have aliases, like there exists one in form of syslog.service.
> For such aliases you just define normal After/Wants/Requires entries.

Such abstract entities / synchronization points are usually defined
using targets.
See man systemd.target and systemd.special

> However I really would start one step before.  What exactly do you think
> a service dependency on "mail-transport-agent" does provide you?
> 
> The virtual package "mail-transport-agent" provides you with
> /usr/sbin/sendmail to send mails.  However to use this interface you
> don't need a service running (and several implementations of this
> interface don't have any service apart from cron).

I agree. Such synchronization points are best avoided if possible.

As a side note: In the past, the systemd package shipped a
mail-transport-agent.target but this was dropped in 229-6

https://salsa.debian.org/systemd-team/systemd/commit/e50c3295026fda0aa67d0c5d8f7a22c6f2e56efa

I would prefer if mail-transport-agent.target was not re-introduced.

Michael
-- 
Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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