Re: [systemd-devel] systemd kills mdmon if it was started manually by user

[Lennart Poettering <lennart@poettering.net>]

On Tue, 08.02.11 16:54, Andrey Borzenkov (arvidjaar@mail.ru) wrote:

> >> a) mdmon is perfectly capable of restarting, it is already used to
> >> take over mdmon launched in initrd. The problem is to know when to
> >> restart - i.e. when respective libraries are changed. This is a job
> >> for package management in distribution. It is already employed for
> >> glibc, systemd and some others and can just as well be employed for
> >> mdmon. And this is totally unrelated to systemd :)
> >
> > Really, you are sying there is a synchronous way to make mdmon reexec
> > itself? How does that work?
> >
> 
> I am not sure whether it qualifies as synchronous, but "mdmon
> --takeover" will kill any existing mdmon for this and start monitoring
> itself.

I wonder if this is really fully synchronous, i.e. that a) there is no
point in time where mdmon is not running during this restart and b) the
mdmom --takeover command returns when the new daemon is fully up, and
not right-away.

> > Well, the root file systems cannot be unmounted, only remounted.
> >
> > So, is there a way to invoke mdmon so that it flushes all metadata
> > changes to disk and immediately terminates then this should be all we
> > need for a clean solution. We'd then shutdown the normal instances of
> > mdmon down like any other daemon and simply invoke this metadata
> > flushing command as part of late shutdown.
> 
> 
> Hmm ... it looks like you just need to
> 
> start mdmon
> do mdadm --wait-clean
> 
> After this you can kill mdmon again (assuming decide is no more in
> use).


Well, it would be nice if the md utils would offer something doing this
without spawning multiple processes and killing them again. 

Lennart

-- 
Lennart Poettering - Red Hat, Inc.