[systemd-devel] Complex supervision structures/delegating watchdog?

[Mantas Mikulėnas]

On Mon, Feb 16, 2015 at 10:36 PM, Holger Hans Peter Freyther <
holger at freyther.de> wrote:

> On Mon, Feb 16, 2015 at 11:21:53AM +0100, Lennart Poettering wrote:
> >
> > Is your pppd daemon itself also a systemd service?
> >
> > What precisely does "monitor" consist of for this case?
>
> Yes, the pppd is invoked by systemd as a service. What I am
> doing right now is:
>
> link.service:
> ExecStart=pppd call uplink ... nodetach
>
> /etc/ppp/ip-up.d/NN-linkmon:
> linkmon -i $PPP_IFACE -d 8.8.8.8 -p `cat /run/${PPP_IFACE}.pid` &
>
>
> The monitoring right now involves simple ICMP request and
> depending on the outcome I change the metric of one of the
> default routes. So in case some amount of packet loss is
> reached the linkmon will SIGKILL the pid provided.
>
> > We have watchdog support already, with sd_notify(0, "WATCHDOG=1"), and
> > WatchdogSec=. But that requires you to run your pppd as a service of
> > its own, to be useful.
>
> I thought the sd_notify is only possible by the "main"
> application that got started? E.g. in the above case the
> linkmon would be a child of pppd. My application wouldn't
> run until pppd has setup the link. This means I would need
> to configure a high enough timeout to cope with a potential
> bigger set-up time.
>

NotifyAccess=


> One nice thing for an external watchdog started by the
> NN-linkmon script would be that it would be under pid1
> control (e.g. if it is crashing, the other service would
> be taken down by systemd), I could have different privileges
> for the monitoring system (currently at least one part of
> it must be able to send a kill to a parent process).
>

You can ask systemd to stop or reload a service.


> Another neat feature would be if applications could
> communicate some extra (custom) status to systemd. E.g.
> in the case of pppd to indicate the state of the link-setup,
> for something like our BTS process to indicate if it is
> currently broadcasting or muted.
>

sd_notify("STATUS=Reticulating splines");

sd_notify("READY=1\nSTATUS=Connected.");

-- 
Mantas Mikulėnas <grawity at gmail.com>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/systemd-devel/attachments/20150216/4f9c31ca/attachment.html>