Re: Creating/restoring snapshots in early userspace

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Dne 08. 08. 22 v 20:14 cd napsal(a):


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


Yep - I think there was a similar issue with Dracut.
It's the side-effect result of making most of default settings as 'commented' - then this scripts stopped to work in such case.

Regards

Zdenek

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