[systemd-devel] Merging journal logs from btrfs snapshots

[Kai Krakow]

Chris Murphy <lists at colorremedies.com> schrieb:

> I tend to keep the original boot, root, home subvolumes as primary. So I
> think it's a bit weird having <FS_TREE>/root/var/log/journal as a
> subvolume that is then mounted on top of itself most of the time - as
> that's the way it would be in order for the fstab of subsequent root
> snapshots to mount the journal subvolume. Otherwise I'd have to change the
> fstab for each snapshot = annoying. So I think I'd put the journal
> subvolume in top level 5, or maybe in some other tree for persistent
> subvolumes to mount.

You understood me wrong but I think we tend to mean the same. ;-)

But it won't get mounted on top of itself. If this is your structure:

<FS_TREE>
  var-log-journal  <-- this is your journal subvolume
  rootfs           <-- rw snapshot aka subvolume
    var
      log
        journal    <-- this is an empty directory
    ...
  home             <-- subvolume

Then you would have in <FS_TREE>/rootfs/etc/fstab always the same mount 
point for the journal:

LABEL=btrfs-pool / subvol=rootfs
LABEL=btrfs-pool /home subvol=home
LABEL=btrfs-pool /var/log/journal subvol=var-log-journal,x-systemd.automount

I understood you that it was all about having the journal independent of 
snapshots taken of "rootfs".

You are right about taking snapshots ro, then rollback by snapshotting rw. 
These are implementation details which would make this even more complicate 
to follow.

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