[systemd-devel] [PATCH] fstab-generator: introduce rd.weak_sysroot to bypass failures in sysroot.mount

Vivek Goyal vgoyal at redhat.com
Tue Jul 30 12:14:13 PDT 2013

On Wed, Jul 31, 2013 at 12:46:22AM +0800, WANG Chao wrote:
> On 07/31/13 at 12:32am, WANG Chao wrote:
> > On 07/30/13 at 03:46pm, Zbigniew Jędrzejewski-Szmek wrote:
> > > On Tue, Jul 30, 2013 at 09:43:16AM -0400, Vivek Goyal wrote:
> > > > [CC harald]
> > > > 
> > > > Not sure if this is right way to do or not but I will give more
> > > > background about the issue.
> > > > 
> > > > This assumption seems to be built into initramfs and systemd that root
> > > > should always be mountable. If one can't mount root, it is a fatal
> > > > failure.
> > > > 
> > > > But in case of kdump initramfs, this assumption is no more valid. Core
> > > > might be being saved to a target which is not root (say over ssh). And
> > > > even if mounting root fails, it is ok.
> > > > 
> > > > So we kind of need a mode (possibly driven by command line option) where
> > > > if mouting root failed, it is ok and continue with mouting other targets
> > > > and kdump module will then handle errors.
> > > Maybe rootfsflags=nofail could do be used as this flag?
> > 
> > rootflags=nofail works. Thanks.
> > 
> > Although it results in a little difference between my approach, I prefer
> > use this one than adding another cmdline param.
> I just find nofail option only works when mnt device doesn't exists.
> What if the filesytem is corrupted? sysroot.mount will and
> initrd-root-fs.target will never reach.


In kdump environment, for most of the users default of dropping into a
shell does not make sense. If some server crashes some where and we are
not able to take dump due to some failure, most of the users will like that
system reboots automatically and services are back up online.

I see that right now rd.action_on_fail is parsed by emergency.service and
service does not start if this parameter is specified.

Can't we interpret this parameter little differently. That is this
parameter modifies the OnFailure= behavior.

So by default OnFailure= is emergency.service which is equivalent to
a shell.

A user can force change of behavior by specifying command line.

rd.action_on_failure=shell (OnFailure=emergency.service)
rd.action_on_failure=reboot (OnFailure=reboot)
rd.action_on_failure=continue (OnFailure=continue)

Now action_on_failure=continue will effectively pretend that unit start
was successful and go ahead with starting next unit. This might be little
contentious though as other dependent units will fail in unknown ways.

Now by default kdump can use rd.acton_on_failure=continue and try to
save dump. If it can't due to previous failures, then it will anyway
reboot the system.

Also if emergency.service stops parsing rd.action_on_failure, then kdump
module will be able to start emergency.service too when it sees there
is a problem. Right now when kdump module tries to start emergency.service
it fails because it looks at acton_on_fail parameter (Another issue Bao is
trying to solve).


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