After shutting down a container, backup.yaml appears in the mount directory

Can you confirm you have done:
sudo snap set lxd daemon.debug=true
sudo systemctl reload snap.lxd.daemon

Yes. I actually rebooted once I saw that the logs were not being generated. The output of sudo snap get lxd daemon.debug is true

Here is the latest snap info in case it matters:
lxd 4.0.1 14954 latest/stable canonical✓ -

Here is the output of journalctl -u snap.lxd.daemon -n 300. The container that just failed is called dev-dwk:

-- Logs begin at Tue 2019-12-24 17:44:54 -03, end at Thu 2020-05-07 11:10:55 -04. --
May 01 09:16:57 cobalt lxd.daemon[3396]: t=2020-05-01T09:16:57-0400 lvl=eror msg="Failed starting container" action=start created=2020-02-10T08:08:03-0300 ephemeral=false name=applications project=default stateful=false used=2020-05-01T09:15:06-0400
May 01 09:16:57 cobalt lxd.daemon[3396]: t=2020-05-01T09:16:57-0400 lvl=eror msg="The stop hook failed" container=applications err="Failed to run: zfs unmount default/containers/applications: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/applications: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/applications': umount failed"
May 01 09:17:09 cobalt lxd.daemon[3396]: t=2020-05-01T09:17:09-0400 lvl=eror msg="Failed starting container" action=start created=2020-02-10T08:08:03-0300 ephemeral=false name=applications project=default stateful=false used=2020-05-01T09:16:56-0400
May 01 09:17:09 cobalt lxd.daemon[3396]: t=2020-05-01T09:17:09-0400 lvl=eror msg="The stop hook failed" container=applications err="Failed to run: zfs unmount default/containers/applications: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/applications: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/applications': umount failed"
May 01 09:17:21 cobalt lxd.daemon[3396]: t=2020-05-01T09:17:21-0400 lvl=eror msg="Failed starting container" action=start created=2020-02-10T08:08:03-0300 ephemeral=false name=applications project=default stateful=false used=2020-05-01T09:17:08-0400
May 01 09:17:21 cobalt lxd.daemon[3396]: t=2020-05-01T09:17:21-0400 lvl=eror msg="The stop hook failed" container=applications err="Failed to run: zfs unmount default/containers/applications: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/applications: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/applications': umount failed"
May 01 09:17:28 cobalt lxd.daemon[3396]: t=2020-05-01T09:17:28-0400 lvl=eror msg="Failed starting container" action=start created=2020-01-19T10:43:11-0300 ephemeral=false name=dev-dwk project=default stateful=false used=2020-05-01T09:10:20-0400
May 01 09:17:29 cobalt lxd.daemon[3396]: t=2020-05-01T09:17:29-0400 lvl=eror msg="The stop hook failed" container=dev-dwk err="Failed to run: zfs unmount default/containers/dev-dwk: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk': umount failed"
May 01 09:18:46 cobalt systemd[1]: Stopping Service for snap application lxd.daemon...
May 01 09:18:47 cobalt lxd.daemon[21064]: => Stop reason is: host shutdown
May 01 09:18:47 cobalt lxd.daemon[21064]: => Stopping LXD (with container shutdown)
May 01 09:18:47 cobalt lxd.daemon[3396]: => LXD exited cleanly
May 01 09:18:48 cobalt lxd.daemon[21064]: ==> Stopped LXD
May 01 09:18:48 cobalt lxd.daemon[21064]: => Stopping LXCFS
May 01 09:18:48 cobalt lxd.daemon[2301]: Running destructor lxcfs_exit
May 01 09:18:49 cobalt lxd.daemon[21064]: ==> Stopped LXCFS
May 01 09:18:49 cobalt lxd.daemon[21064]: => Cleaning up PID files
May 01 09:18:49 cobalt lxd.daemon[21064]: => Cleaning up namespaces
May 01 09:18:49 cobalt lxd.daemon[21064]: => All done
May 01 09:18:49 cobalt systemd[1]: snap.lxd.daemon.service: Succeeded.
May 01 09:18:49 cobalt systemd[1]: Stopped Service for snap application lxd.daemon.
-- Reboot --
May 01 09:20:45 cobalt systemd[1]: Started Service for snap application lxd.daemon.
May 01 09:20:45 cobalt lxd.daemon[3612]: => Preparing the system (14890)
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Loading snap configuration
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up mntns symlink (mnt:[4026532795])
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up mount propagation on /var/snap/lxd/common/lxd/storage-pools
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up mount propagation on /var/snap/lxd/common/lxd/devices
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up persistent shmounts path
May 01 09:20:45 cobalt lxd.daemon[3612]: ====> Making LXD shmounts use the persistent path
May 01 09:20:45 cobalt lxd.daemon[3612]: ====> Making LXCFS use the persistent path
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up kmod wrapper
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Preparing /boot
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Preparing a clean copy of /run
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Preparing a clean copy of /etc
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Preparing a clean copy of /usr/share/misc
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up ceph configuration
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up LVM configuration
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Rotating logs
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Setting up ZFS (0.8)
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Escaping the systemd cgroups
May 01 09:20:45 cobalt lxd.daemon[3612]: ====> Detected cgroup V1
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Escaping the systemd process resource limits
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Increasing the number of inotify user instances
May 01 09:20:45 cobalt lxd.daemon[3612]: ==> Disabling shiftfs on this kernel (auto)
May 01 09:20:45 cobalt lxd.daemon[3612]: => Starting LXCFS
May 01 09:20:45 cobalt lxd.daemon[3612]: Running constructor lxcfs_init to reload liblxcfs
May 01 09:20:45 cobalt lxd.daemon[3612]: mount namespace: 4
May 01 09:20:45 cobalt lxd.daemon[3612]: hierarchies:
May 01 09:20:45 cobalt lxd.daemon[3612]:   0: fd:   5:
May 01 09:20:45 cobalt lxd.daemon[3612]:   1: fd:   6: name=systemd
May 01 09:20:45 cobalt lxd.daemon[3612]:   2: fd:   7: rdma
May 01 09:20:45 cobalt lxd.daemon[3612]:   3: fd:   8: cpu,cpuacct
May 01 09:20:45 cobalt lxd.daemon[3612]:   4: fd:   9: memory
May 01 09:20:45 cobalt lxd.daemon[3612]:   5: fd:  10: devices
May 01 09:20:45 cobalt lxd.daemon[3612]:   6: fd:  11: freezer
May 01 09:20:45 cobalt lxd.daemon[3612]:   7: fd:  12: net_cls,net_prio
May 01 09:20:45 cobalt lxd.daemon[3612]:   8: fd:  13: blkio
May 01 09:20:45 cobalt lxd.daemon[3612]:   9: fd:  14: cpuset
May 01 09:20:45 cobalt lxd.daemon[3612]:  10: fd:  15: perf_event
May 01 09:20:45 cobalt lxd.daemon[3612]:  11: fd:  16: pids
May 01 09:20:45 cobalt lxd.daemon[3612]:  12: fd:  17: hugetlb
May 01 09:20:45 cobalt lxd.daemon[3612]: Kernel supports pidfds
May 01 09:20:45 cobalt lxd.daemon[3612]: api_extensions:
May 01 09:20:45 cobalt lxd.daemon[3612]: - cgroups
May 01 09:20:45 cobalt lxd.daemon[3612]: - sys_cpu_online
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_cpuinfo
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_diskstats
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_loadavg
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_meminfo
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_stat
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_swaps
May 01 09:20:45 cobalt lxd.daemon[3612]: - proc_uptime
May 01 09:20:45 cobalt lxd.daemon[3612]: - shared_pidns
May 01 09:20:45 cobalt lxd.daemon[3612]: - cpuview_daemon
May 01 09:20:45 cobalt lxd.daemon[3612]: - loadavg_daemon
May 01 09:20:45 cobalt lxd.daemon[3612]: - pidfds
May 01 09:20:46 cobalt lxd.daemon[3612]: => Starting LXD
May 01 09:20:47 cobalt lxd.daemon[3612]: t=2020-05-01T09:20:47-0400 lvl=warn msg=" - Couldn't find the CGroup blkio.weight, I/O weight limits will be ignored"
May 01 09:20:47 cobalt lxd.daemon[3612]: t=2020-05-01T09:20:47-0400 lvl=warn msg=" - Couldn't find the CGroup memory swap accounting, swap limits will be ignored"
May 01 09:20:47 cobalt lxd.daemon[3612]: t=2020-05-01T09:20:47-0400 lvl=eror msg="Firewall nftables unable to parse existing ruleset: invalid character '^' looking for beginning of value"
May 01 09:20:49 cobalt lxd.daemon[3612]: => LXD is ready
May 01 09:28:33 cobalt lxd.daemon[3612]: t=2020-05-01T09:28:33-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 02 07:19:08 cobalt lxd.daemon[3612]: proc_fuse.c: 877: proc_stat_read: cpu1 from /lxc.payload.dev-dwk has unexpected cpu time: 1127694 in /proc/stat, 1128451 in cpuacct.usage_all; unable to determine idle time
May 02 07:19:08 cobalt lxd.daemon[3612]: proc_fuse.c: 877: proc_stat_read: cpu2 from /lxc.payload.dev-dwk has unexpected cpu time: 1112896 in /proc/stat, 1172677 in cpuacct.usage_all; unable to determine idle time
May 05 10:47:42 cobalt lxd.daemon[3612]: t=2020-05-05T10:47:42-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 10:48:48 cobalt lxd.daemon[3612]: t=2020-05-05T10:48:48-0400 lvl=eror msg="Failed shutting down container" action=shutdown created=2020-04-21T12:04:33-0400 ephemeral=false name=dev-ppe project=default timeout=15s used=2020-05-02T10:53:41-0400
May 05 10:54:19 cobalt systemd[1]: Stopping Service for snap application lxd.daemon...
May 05 10:54:19 cobalt lxd.daemon[23601]: => Stop reason is: host shutdown
May 05 10:54:19 cobalt lxd.daemon[23601]: => Stopping LXD (with container shutdown)
May 05 10:54:20 cobalt lxd.daemon[3612]: => LXD exited cleanly
May 05 10:54:20 cobalt lxd.daemon[23601]: ==> Stopped LXD
May 05 10:54:20 cobalt lxd.daemon[23601]: => Stopping LXCFS
May 05 10:54:20 cobalt lxd.daemon[3612]: Running destructor lxcfs_exit
May 05 10:54:21 cobalt lxd.daemon[23601]: ==> Stopped LXCFS
May 05 10:54:21 cobalt lxd.daemon[23601]: => Cleaning up PID files
May 05 10:54:21 cobalt lxd.daemon[23601]: => Cleaning up namespaces
May 05 10:54:21 cobalt lxd.daemon[23601]: => All done
May 05 10:54:21 cobalt systemd[1]: snap.lxd.daemon.service: Succeeded.
May 05 10:54:21 cobalt systemd[1]: Stopped Service for snap application lxd.daemon.
-- Reboot --
May 05 10:55:49 cobalt systemd[1]: Started Service for snap application lxd.daemon.
May 05 10:55:49 cobalt lxd.daemon[3442]: => Preparing the system (14890)
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Loading snap configuration
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up mntns symlink (mnt:[4026532805])
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up mount propagation on /var/snap/lxd/common/lxd/storage-pools
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up mount propagation on /var/snap/lxd/common/lxd/devices
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up persistent shmounts path
May 05 10:55:49 cobalt lxd.daemon[3442]: ====> Making LXD shmounts use the persistent path
May 05 10:55:49 cobalt lxd.daemon[3442]: ====> Making LXCFS use the persistent path
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up kmod wrapper
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Preparing /boot
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Preparing a clean copy of /run
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Preparing a clean copy of /etc
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Preparing a clean copy of /usr/share/misc
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up ceph configuration
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up LVM configuration
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Rotating logs
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Setting up ZFS (0.8)
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Escaping the systemd cgroups
May 05 10:55:49 cobalt lxd.daemon[3442]: ====> Detected cgroup V1
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Escaping the systemd process resource limits
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Increasing the number of inotify user instances
May 05 10:55:49 cobalt lxd.daemon[3442]: ==> Disabling shiftfs on this kernel (auto)
May 05 10:55:49 cobalt lxd.daemon[3442]: => Starting LXCFS
May 05 10:55:49 cobalt lxd.daemon[3442]: Running constructor lxcfs_init to reload liblxcfs
May 05 10:55:49 cobalt lxd.daemon[3442]: mount namespace: 4
May 05 10:55:49 cobalt lxd.daemon[3442]: hierarchies:
May 05 10:55:49 cobalt lxd.daemon[3442]:   0: fd:   5:
May 05 10:55:49 cobalt lxd.daemon[3442]:   1: fd:   6: name=systemd
May 05 10:55:49 cobalt lxd.daemon[3442]:   2: fd:   7: pids
May 05 10:55:49 cobalt lxd.daemon[3442]:   3: fd:   8: devices
May 05 10:55:49 cobalt lxd.daemon[3442]:   4: fd:   9: blkio
May 05 10:55:49 cobalt lxd.daemon[3442]:   5: fd:  10: perf_event
May 05 10:55:49 cobalt lxd.daemon[3442]:   6: fd:  11: memory
May 05 10:55:49 cobalt lxd.daemon[3442]:   7: fd:  12: net_cls,net_prio
May 05 10:55:49 cobalt lxd.daemon[3442]:   8: fd:  13: rdma
May 05 10:55:49 cobalt lxd.daemon[3442]:   9: fd:  14: hugetlb
May 05 10:55:49 cobalt lxd.daemon[3442]:  10: fd:  15: cpu,cpuacct
May 05 10:55:49 cobalt lxd.daemon[3442]:  11: fd:  16: freezer
May 05 10:55:49 cobalt lxd.daemon[3442]:  12: fd:  17: cpuset
May 05 10:55:49 cobalt lxd.daemon[3442]: Kernel supports pidfds
May 05 10:55:49 cobalt lxd.daemon[3442]: api_extensions:
May 05 10:55:49 cobalt lxd.daemon[3442]: - cgroups
May 05 10:55:49 cobalt lxd.daemon[3442]: - sys_cpu_online
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_cpuinfo
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_diskstats
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_loadavg
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_meminfo
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_stat
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_swaps
May 05 10:55:49 cobalt lxd.daemon[3442]: - proc_uptime
May 05 10:55:49 cobalt lxd.daemon[3442]: - shared_pidns
May 05 10:55:49 cobalt lxd.daemon[3442]: - cpuview_daemon
May 05 10:55:49 cobalt lxd.daemon[3442]: - loadavg_daemon
May 05 10:55:49 cobalt lxd.daemon[3442]: - pidfds
May 05 10:55:50 cobalt lxd.daemon[3442]: => Starting LXD
May 05 10:55:50 cobalt lxd.daemon[3442]: t=2020-05-05T10:55:50-0400 lvl=warn msg=" - Couldn't find the CGroup blkio.weight, I/O weight limits will be ignored"
May 05 10:55:50 cobalt lxd.daemon[3442]: t=2020-05-05T10:55:50-0400 lvl=warn msg=" - Couldn't find the CGroup memory swap accounting, swap limits will be ignored"
May 05 10:55:51 cobalt lxd.daemon[3442]: t=2020-05-05T10:55:51-0400 lvl=eror msg="Firewall nftables unable to parse existing ruleset: invalid character '^' looking for beginning of value"
May 05 10:55:53 cobalt lxd.daemon[3442]: => LXD is ready
May 05 11:00:28 cobalt lxd.daemon[3442]: t=2020-05-05T11:00:28-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:21:49 cobalt lxd.daemon[3442]: t=2020-05-05T11:21:49-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:25:13 cobalt lxd.daemon[3442]: t=2020-05-05T11:25:13-0400 lvl=eror msg="Error getting source image" err="No such object" fp=d158b6b8ddb791e2efa66c9c623c479388d6b01b32a11785b251c4daad723146
May 05 11:25:26 cobalt lxd.daemon[3442]: t=2020-05-05T11:25:26-0400 lvl=eror msg="Error getting source image" err="No such object" fp=d158b6b8ddb791e2efa66c9c623c479388d6b01b32a11785b251c4daad723146
May 05 11:25:30 cobalt lxd.daemon[3442]: t=2020-05-05T11:25:30-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 05 11:27:36 cobalt lxd.daemon[3442]: t=2020-05-05T11:27:36-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:27:36 cobalt lxd.daemon[3442]: t=2020-05-05T11:27:36-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:27:49 cobalt lxd.daemon[3442]: t=2020-05-05T11:27:49-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:27:49 cobalt lxd.daemon[3442]: t=2020-05-05T11:27:49-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:30:30 cobalt lxd.daemon[3442]: t=2020-05-05T11:30:30-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:30:44 cobalt lxd.daemon[3442]: t=2020-05-05T11:30:44-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:30:44 cobalt lxd.daemon[3442]: t=2020-05-05T11:30:44-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:32:55 cobalt lxd.daemon[3442]: t=2020-05-05T11:32:55-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:33:11 cobalt lxd.daemon[3442]: t=2020-05-05T11:33:11-0400 lvl=eror msg="Failed shutting down container" action=shutdown created=2020-05-05T11:30:25-0400 ephemeral=false name=test project=default timeout=15s used=2020-05-05T11:32:50-0400
May 05 11:33:55 cobalt lxd.daemon[3442]: t=2020-05-05T11:33:55-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 11:33:55 cobalt lxd.daemon[3442]: t=2020-05-05T11:33:55-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:10:37 cobalt lxd.daemon[3442]: t=2020-05-05T14:10:37-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:10:37 cobalt lxd.daemon[3442]: t=2020-05-05T14:10:37-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:12:08 cobalt lxd.daemon[3442]: t=2020-05-05T14:12:08-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:14:26 cobalt lxd.daemon[3442]: t=2020-05-05T14:14:26-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:24:34 cobalt lxd.daemon[3442]: t=2020-05-05T14:24:34-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:24:55 cobalt lxd.daemon[3442]: t=2020-05-05T14:24:55-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:29:06 cobalt lxd.daemon[3442]: t=2020-05-05T14:29:06-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:29:48 cobalt lxd.daemon[3442]: t=2020-05-05T14:29:48-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:32:32 cobalt lxd.daemon[3442]: t=2020-05-05T14:32:32-0400 lvl=warn msg="Detected poll(POLLNVAL) event: exiting."
May 05 14:33:03 cobalt lxd.daemon[3442]: t=2020-05-05T14:33:03-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:36:59 cobalt lxd.daemon[3442]: t=2020-05-05T14:36:59-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:37:09 cobalt lxd.daemon[3442]: t=2020-05-05T14:37:09-0400 lvl=eror msg="Error getting disk usage" err="Failed to run: zfs get -H -p -o value used default/containers/dev-xnerds: cannot open 'default/containers/dev-xnerds': dataset does not exist" instance=dev-xnerds project=default
May 05 14:38:33 cobalt lxd.daemon[3442]: t=2020-05-05T14:38:33-0400 lvl=warn msg="Detected poll(POLLNVAL) event: exiting."
May 05 14:42:06 cobalt lxd.daemon[3442]: t=2020-05-05T14:42:06-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:42:06 cobalt lxd.daemon[3442]: t=2020-05-05T14:42:06-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:42:24 cobalt lxd.daemon[3442]: t=2020-05-05T14:42:24-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:42:24 cobalt lxd.daemon[3442]: t=2020-05-05T14:42:24-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:45:21 cobalt lxd.daemon[3442]: t=2020-05-05T14:45:21-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:46:21 cobalt lxd.daemon[3442]: t=2020-05-05T14:46:21-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:47:50 cobalt lxd.daemon[3442]: t=2020-05-05T14:47:50-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:47:50 cobalt lxd.daemon[3442]: t=2020-05-05T14:47:50-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:51:56 cobalt lxd.daemon[3442]: t=2020-05-05T14:51:56-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:53:55 cobalt lxd.daemon[3442]: t=2020-05-05T14:53:55-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 14:54:19 cobalt lxd.daemon[3442]: t=2020-05-05T14:54:19-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:06:09 cobalt lxd.daemon[3442]: t=2020-05-05T15:06:09-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:07:05 cobalt lxd.daemon[3442]: t=2020-05-05T15:07:05-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:07:08 cobalt lxd.daemon[3442]: t=2020-05-05T15:07:08-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:07:14 cobalt lxd.daemon[3442]: t=2020-05-05T15:07:14-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:07:14 cobalt lxd.daemon[3442]: t=2020-05-05T15:07:14-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:07:34 cobalt lxd.daemon[3442]: t=2020-05-05T15:07:34-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:19:39 cobalt lxd.daemon[3442]: t=2020-05-05T15:19:39-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:21:36 cobalt lxd.daemon[3442]: t=2020-05-05T15:21:36-0400 lvl=warn msg="Detected poll(POLLNVAL) event: exiting."
May 05 15:26:31 cobalt lxd.daemon[3442]: t=2020-05-05T15:26:31-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:29:50 cobalt lxd.daemon[3442]: t=2020-05-05T15:29:50-0400 lvl=warn msg="Detected poll(POLLNVAL) event: exiting."
May 05 15:30:28 cobalt lxd.daemon[3442]: t=2020-05-05T15:30:28-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:31:21 cobalt lxd.daemon[3442]: t=2020-05-05T15:31:21-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:33:48 cobalt lxd.daemon[3442]: t=2020-05-05T15:33:48-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 15:36:52 cobalt lxd.daemon[3442]: t=2020-05-05T15:36:52-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 05 16:55:52 cobalt lxd.daemon[3442]: t=2020-05-05T16:55:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 05 20:30:32 cobalt systemd[1]: Stopping Service for snap application lxd.daemon...
May 05 20:30:32 cobalt lxd.daemon[18100]: => Stop reason is: snap refresh
May 05 20:30:32 cobalt lxd.daemon[18100]: => Stopping LXD
May 05 20:30:32 cobalt lxd.daemon[3442]: => LXD exited cleanly
May 05 20:30:33 cobalt systemd[1]: snap.lxd.daemon.service: Succeeded.
May 05 20:30:33 cobalt systemd[1]: Stopped Service for snap application lxd.daemon.
May 05 20:30:50 cobalt systemd[1]: Started Service for snap application lxd.daemon.
May 05 20:30:50 cobalt lxd.daemon[18863]: => Preparing the system (14954)
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Loading snap configuration
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up mntns symlink (mnt:[4026532805])
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up mount propagation on /var/snap/lxd/common/lxd/storage-pools
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up mount propagation on /var/snap/lxd/common/lxd/devices
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up kmod wrapper
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Preparing /boot
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Preparing a clean copy of /run
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Preparing a clean copy of /etc
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Preparing a clean copy of /usr/share/misc
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up ceph configuration
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up LVM configuration
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Rotating logs
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Setting up ZFS (0.8)
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Escaping the systemd cgroups
May 05 20:30:50 cobalt lxd.daemon[18863]: ====> Detected cgroup V1
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Escaping the systemd process resource limits
May 05 20:30:50 cobalt lxd.daemon[18863]: ==> Disabling shiftfs on this kernel (auto)
May 05 20:30:50 cobalt lxd.daemon[18863]: => Re-using existing LXCFS
May 05 20:30:50 cobalt lxd.daemon[18863]: => Starting LXD
May 05 20:30:50 cobalt lxd.daemon[18863]: t=2020-05-05T20:30:50-0400 lvl=warn msg=" - Couldn't find the CGroup blkio.weight, I/O weight limits will be ignored"
May 05 20:30:50 cobalt lxd.daemon[18863]: t=2020-05-05T20:30:50-0400 lvl=warn msg=" - Couldn't find the CGroup memory swap accounting, swap limits will be ignored"
May 05 20:30:51 cobalt lxd.daemon[18863]: t=2020-05-05T20:30:51-0400 lvl=eror msg="Firewall nftables unable to parse existing ruleset: invalid character '^' looking for beginning of value"
May 05 20:30:52 cobalt lxd.daemon[18863]: t=2020-05-05T20:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 05 20:30:52 cobalt lxd.daemon[18863]: => LXD is ready
May 05 20:31:47 cobalt lxd.daemon[3442]: Closed liblxcfs.so
May 05 20:31:47 cobalt lxd.daemon[3442]: Running destructor lxcfs_exit
May 05 20:31:47 cobalt lxd.daemon[3442]: Running constructor lxcfs_init to reload liblxcfs
May 05 20:31:47 cobalt lxd.daemon[3442]: mount namespace: 5
May 05 20:31:47 cobalt lxd.daemon[3442]: hierarchies:
May 05 20:31:47 cobalt lxd.daemon[3442]:   0: fd:   6:
May 05 20:31:47 cobalt lxd.daemon[3442]:   1: fd:   7: name=systemd
May 05 20:31:47 cobalt lxd.daemon[3442]:   2: fd:   8: pids
May 05 20:31:47 cobalt lxd.daemon[3442]:   3: fd:   9: devices
May 05 20:31:47 cobalt lxd.daemon[3442]:   4: fd:  10: blkio
May 05 20:31:47 cobalt lxd.daemon[3442]:   5: fd:  11: perf_event
May 05 20:31:47 cobalt lxd.daemon[3442]:   6: fd:  12: memory
May 05 20:31:47 cobalt lxd.daemon[3442]:   7: fd:  13: net_cls,net_prio
May 05 20:31:47 cobalt lxd.daemon[3442]:   8: fd:  14: rdma
May 05 20:31:47 cobalt lxd.daemon[3442]:   9: fd:  15: hugetlb
May 05 20:31:47 cobalt lxd.daemon[3442]:  10: fd:  16: cpu,cpuacct
May 05 20:31:47 cobalt lxd.daemon[3442]:  11: fd:  17: freezer
May 05 20:31:47 cobalt lxd.daemon[3442]:  12: fd:  19: cpuset
May 05 20:31:47 cobalt lxd.daemon[3442]: Kernel supports pidfds
May 05 20:31:47 cobalt lxd.daemon[3442]: api_extensions:
May 05 20:31:47 cobalt lxd.daemon[3442]: - cgroups
May 05 20:31:47 cobalt lxd.daemon[3442]: - sys_cpu_online
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_cpuinfo
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_diskstats
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_loadavg
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_meminfo
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_stat
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_swaps
May 05 20:31:47 cobalt lxd.daemon[3442]: - proc_uptime
May 05 20:31:47 cobalt lxd.daemon[3442]: - shared_pidns
May 05 20:31:47 cobalt lxd.daemon[3442]: - cpuview_daemon
May 05 20:31:47 cobalt lxd.daemon[3442]: - loadavg_daemon
May 05 20:31:47 cobalt lxd.daemon[3442]: - pidfds
May 05 20:31:47 cobalt lxd.daemon[3442]: Reloaded LXCFS
May 05 21:57:40 cobalt lxd.daemon[18863]: t=2020-05-05T21:57:40-0400 lvl=warn msg="Detected poll(POLLNVAL) event: exiting."
May 06 02:30:52 cobalt lxd.daemon[18863]: t=2020-05-06T02:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 06 08:30:52 cobalt lxd.daemon[18863]: t=2020-05-06T08:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 06 10:41:09 cobalt lxd.daemon[18863]: t=2020-05-06T10:41:09-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 06 14:30:52 cobalt lxd.daemon[18863]: t=2020-05-06T14:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 06 20:30:52 cobalt lxd.daemon[18863]: t=2020-05-06T20:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 07 02:30:52 cobalt lxd.daemon[18863]: t=2020-05-07T02:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 07 08:30:52 cobalt lxd.daemon[18863]: t=2020-05-07T08:30:52-0400 lvl=eror msg="Error getting source image" err="No such object" fp=db68e16f19f5b6e54300949335c35c3037a0bb07866633ae3835c733a9bac11d
May 07 09:31:00 cobalt lxd.daemon[18863]: t=2020-05-07T09:31:00-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 07 10:36:00 cobalt lxd.daemon[18863]: t=2020-05-07T10:36:00-0400 lvl=warn msg="Detected poll(POLLNVAL) event: exiting."
May 07 10:36:00 cobalt lxd.daemon[18863]: t=2020-05-07T10:36:00-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 07 10:42:07 cobalt lxd.daemon[18863]: t=2020-05-07T10:42:07-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 07 11:05:24 cobalt lxd.daemon[18863]: t=2020-05-07T11:05:24-0400 lvl=warn msg="Detected poll(POLLNVAL) event."
May 07 11:05:33 cobalt lxd.daemon[18863]: t=2020-05-07T11:05:33-0400 lvl=eror msg="The stop hook failed" container=dev-dwk err="Failed to run: zfs unmount default/containers/dev-dwk: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk': umount failed"
May 07 11:05:34 cobalt lxd.daemon[18863]: t=2020-05-07T11:05:34-0400 lvl=eror msg="Failed starting container" action=start created=2020-01-19T10:43:11-0300 ephemeral=false name=dev-dwk project=default stateful=false used=2020-05-05T15:35:48-0400
May 07 11:05:34 cobalt lxd.daemon[18863]: t=2020-05-07T11:05:34-0400 lvl=eror msg="The stop hook failed" container=dev-dwk err="Failed to run: zfs unmount default/containers/dev-dwk: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk': umount failed"
May 07 11:10:05 cobalt lxd.daemon[18863]: t=2020-05-07T11:10:05-0400 lvl=eror msg="Failed starting container" action=start created=2020-01-19T10:43:11-0300 ephemeral=false name=dev-dwk project=default stateful=false used=2020-05-07T11:05:34-0400
May 07 11:10:06 cobalt lxd.daemon[18863]: t=2020-05-07T11:10:06-0400 lvl=eror msg="The stop hook failed" container=dev-dwk err="Failed to run: zfs unmount default/containers/dev-dwk: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk': umount failed"
May 07 11:10:54 cobalt lxd.daemon[18863]: t=2020-05-07T11:10:54-0400 lvl=eror msg="Failed starting container" action=start created=2020-01-19T10:43:11-0300 ephemeral=false name=dev-dwk project=default stateful=false used=2020-05-07T11:10:05-0400
May 07 11:10:55 cobalt lxd.daemon[18863]: t=2020-05-07T11:10:55-0400 lvl=eror msg="The stop hook failed" container=dev-dwk err="Failed to run: zfs unmount default/containers/dev-dwk: umount: /home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk: not mounted.\ncannot unmount '/home/snap/lxd/common/lxd/storage-pools/default/containers/dev-dwk': umount failed"

Thanks.

Its strange you’re still not seeing debug messages. @stgraber any ideas on where these debug messages may be going?

Anyway, I think we can certainly see an issue here with the ZFS unmount failing.

@stgraber maybe your commit https://github.com/lxc/lxd/commit/7de16487fb69bd3c4895a76627e2302829433151 from the other day may help this situation? Perhaps it is still busy.

Regarding the debug messages, I suspect that for some weird reason, sudo snap set ... seems to not convey the values to the snap on my system. I say that because I tried to enable CRIU before, following the directions to run sudo snap set lxd criu.enable=true and the snap never recoginzed it as enabled. It feels like the same thing is happening here.

I’m on Pop OS, which (as you probably know) is a lightly modified derivative of Ubuntu, in case it makes a difference (which I doubt).

I’m not sure if because of recent code changes or some other reason, but this seems to have stabilized recently. I’m not seeing it like I used to. If it continues good for a while longer, I’ll close the thread.

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