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

[Harald Hoyer]

On 07/30/2013 09:14 PM, Vivek Goyal wrote:
> 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.
> 
> Right.
> 
> 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).
> 
> Thanks
> Vivek
> 

Why not install your own version of emergency.service in the kdump dracut
module, which parses rd.action_on_failure and acts accordingly. Or replace
emergency.service in the dracut cmdline hook according to rd.action_on_failure.