Re: [linux-lvm] Creating/restoring snapshots in early userspace

[cd <cd@terminal.space>]

>
>
> Dne 07. 08. 22 v 22:38 cd napsal(a):
>
> > Hello,
> >
> > I have created some scripts which runs in the initramfs during the boot process. Very specifically, it's an initcpio runtime hook https://man.archlinux.org/man/mkinitcpio.8#ABOUT_RUNTIME_HOOKS
> > Question: Is this a supported environment which to create/restore snapshots?
> >
> > When my script runs lvm lvconvert --merge testvg/lvmautosnap-root-1659902622-good
> > it appears to succeed (exit code is 0, and the restore appears to work properly). However, the following warnings appear in stderr as part of the restore process:
> >
> > /usr/bin/dmeventd: stat failed: No such file or directory
> > WARNING: Failed to unmonitor testvg/lvmautosnap-root-1659902622-good.
> > /usr/bin/dmeventd: stat failed: No such file or directory
>
>
> Hi
>
> Your initramfs likely needs to contain 'modified' version of your system's
> lvm.conf where 'monitoring' will be disabled (set to 0) - as you do not want
> to start your monitoring while you are operating in your ramdisk.
>
> Once you flip to your rootfs with your regular /etc/lvm/lvm.conf - you need
> to start monitoring of you activated LVs (vgchange --monitor y)
>
> > Merging of volume testvg/lvmautosnap-root-1659902622-good started.
> > /run/lvm/lvmpolld.socket: connect failed: No such file or directory
>
>
> Again a thing you do not want to run in your ramdisk - lvmpolld is another
> service/daemon you should run while you are in your rootfs.
>
> fully removed.
>
> > And I get similar errors when trying to create new volumes with lvm lvcreate --permission=r --snapshot --monitor n --name my_snapshot
> > /usr/bin/dmeventd: stat failed: No such file or directory
> >
> > In summary, I'm happy to just ignore the warning messages. I just want to make sure I'm not risking the integrity of the lvm volumes by modifying them during this part of the boot process.
>
>
> It looks like you are trying to do something in your ramdisk you really should
> be doing once you flip to your rootfs - ramdisk is purely meant to be used
> to get things 'booting' and flip to rootfs ASAP - doing things in your
> ramdisk which is really not a 'working environment' sounds like you are
> asking yourself for some big troubles with resolving error paths (i.e. using
> unmonitored devices like 'snapshot/mirror/raids/thin...' for longer period of
> time is simply 'bad design/plan' - switch to rootfs should happen quickly
> after you initiate things in your initramdfs...
>
> Regards
>
> Zdenek

Thanks for the insightful response. Indeed, setting monitoring = 0 in lvm.conf makes the warning messages go away. Interestingly, on arch, the initcpio hook for lvm2 _does_ attempt to set this setting:
with sed -i '/^\smonitoring =/s/1/0/' "${BUILDROOT}/etc/lvm/lvm.conf"
https://github.com/archlinux/svntogit-packages/blob/packages/lvm2/trunk/lvm2_install#L38

However, the sed pattern fails to match because the line is commented out in lvm.conf.
I've filed a bug with arch to address this: https://bugs.archlinux.org/task/75552?project=1&string=lvm2

Thanks again!
Anil

_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/