On 1/9/19 11:00 AM, Simon Matter via CentOS wrote:
On Wed, Jan 09, 2019 at 10:43:38AM -0500, Steve Clark wrote:
I am trying to understand what After= means in a unit file. Does it
mean after the specified target is up and operational or only that
the target has been started?
I have something that needs postgres but postgres needs to be
operational not just started. Sometimes it can take a bit for
postgres to become operational.
I believe that the postgresql service has Type=notify in it's service
definition, which means that it will notify systemd when it is
operational. This means that if you have a service that has
After=postgresql.service, systemd should wait until after the
postgresql service notifies systemd that it is operational before your
service will be started.
If your service is starting and unable to connect to postgresql, then
I would say that's a bug in postgresql -- it shouldn't be notifying
systemd that it is operational until it actually is.
This is, in fact, one of the points why I'm very unhappy with systemd and
the way it is implemented here and most likely in most distributions.
Maybe things _could_ be done the right way with systemd, but it doesn't
happen because it quickly starts to be very complex and it's a lot of work
to do it for a complete distribution. It just doesn't happen - or at least
did not happen in all the years since its introduction.
Yes, introduction of systemd earned Linuxes a lot of refugees. I in my
worst times feel maybe that was the goal of it. But then I think about a
split of refugees from Linux to UNIX descendants (FreeBSD, NettBSD etc.)
vs to MS products, and I am not quite certain if that was a goal (though
I do remember MS alliance with RedHat...), but if it was the goal I
doubt refugee split was in MS favor (though one says something is better
than nothing).
I hope, this didn't come as a rant, I should probably have used rant
tags ;-)
Valeri
In this example, PG gets just started with "pg_ctl start" and that's it.
Regards,
Simon
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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
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