Bug 1365297

Hey lvm team, any chance we could support storing this data in `/var/lib/lvm`?  For more information, see https://ostree.readthedocs.io/en/latest/manual/adapting-existing/

At some point we'll probably tweak the ostree process such that we only do the config merge before rebooting.  This would obviate this problem as well as the "config changes i make after preparing an upgrade are gone".

But there are other advantages of having lvm store state in /var - we don't copy it at all, and it's also not something administrators should edit with `vi` etc.

IIRC the important difference here is /etc is "guaranteed" to be on the / filesystem whereas /var is not.  For low-level facilities (like LVM) I can see an argument for wanting to possibly ease the pain for a (probably) small-number of cases where someone's important data is on the line.  

However, this problem is also likely reproducible using any tool/service that writes/changes/moves/locks files under /etc during an update.  Which is why I'm fine with a WONTFIX / "Don't do that" (i.e. docs) resolution.  I guess it depends how much low-level and manual-recovery options we want to enable/support on this platform.

Set LVM_SYSTEM_DIR:

       LVM_SYSTEM_DIR
              Directory containing lvm.conf(5) and other LVM system files.  
              Defaults to "/etc/lvm".

man 7 lvm.

Err, man *8* lvm..

I think NOTABUG is fine.

Maybe we should have a feature to configure LVM_SYSTEM_DIR in the atomic image to point at /var/... ?

Otherwise it's probably more practical to simply recommend not touching storage while you're running the os-tree update.  I'll see about getting this into the knowledge base in case a customer hits it.

Looks great, thanks Derrick.

I have this issue on 2 centos atomic nodes today.
The root partition has been extended lately because it was full:

-bash-4.2# lvs
  LV          VG   Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  docker-pool cah  twi-aot--- 64.60g             85.85  53.13
  root        cah  -wi-ao---- 10.00g
  swap        cah  -wi-ao----  5.00g

Now we have enough space:

-bash-4.2# df -h
Filesystem                                      Size  Used Avail Use% Mounted on
/dev/mapper/cah-root                             10G  7.0G  3.0G  71% /
devtmpfs                                        3.9G     0  3.9G   0% /dev
tmpfs                                           3.9G     0  3.9G   0% /dev/shm
tmpfs                                           3.9G  4.3M  3.9G   1% /run
tmpfs                                           3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/sda1                                       297M  146M  152M  49% /boot
[...]

and I'm NOT in the middle of a lvm expansion (or else I missed a command after `xfs_growfs /`):

-bash-4.2# atomic host upgrade -r
Updating from: centos-atomic-host:centos-atomic-host/7/x86_64/standard
1 metadata, 0 content objects fetched; 313 B transferred in 0 seconds
Copying /etc changes: 26 modified, 4 removed, 179400 added
error: During /etc merge: Failed to read modified config file 'lvm/archive/.lvm_atomic-test-node-2.priv.tech-angels.net_967_1993706434': No such file or directory

Thanks

Oh, now that is interesting!  Right, because the thin-pool auto-extends, so if that were to happen at the same time as the upgrade, you'd hit this.

The error is a TOCTOU race on the temp/lock file.  Probably the code just needs to catch that error and refresh / retry the copy.

So, clearly not as "corner-case" of a problem as I thought.  Okay, re-opening this for further investigation.

I think the correct component is probably 'ostree' for this.

This will be fixed by https://github.com/ostreedev/ostree/issues/545

This is related to /etc merge before reboot.

After evaluating this issue, there are no plans to address it further or fix it in an upcoming release.  Therefore, it is being closed.  If plans change such that this issue will be fixed in an upcoming release, then the bug can be reopened.