Snap install failing; empty /tmp directories

While performing do-release-update from ubuntu-server 18.04 -> 20.04 I encountered an error as shown in the console image attached.

After the upgrade and a reboot I now have the following situation:

$ sudo snap install lxd
error: cannot perform the following tasks:
- Run install hook of "lxd" snap if present (run hook "install": cannot perform operation: mount -- rbind /run/netns /tmp/snap.rootfs_MydTzh//run/netns: No such file or directory)

A symptom that seems to be relevant:

$ sudo ls -l /tmp/snap.rootfs_*
total 0

total 0

total 0

total 0

total 0

Does /run/netns exist in the system?

Only as a broken symlink:

$ ls /run/netns -l
lrwxrwxrwx 1 root root 21 Feb  1 12:59 /run/netns -> /rootfs/var/run/netns
$ ls /rootfs
ls: cannot access '/rootfs': No such file or directory

Is this some sort of container?

No, it is quite a beefy physical server.

Not sure if this df -houtput will provide some clues:

$ df -h
Filesystem                               Size  Used Avail Use% Mounted on
udev                                     126G     0  126G   0% /dev
tmpfs                                     26G  3.3M   26G   1% /run
/dev/mapper/jerry--vg-root                11T  7.3T  2.8T  73% /
tmpfs                                    126G     0  126G   0% /dev/shm
tmpfs                                    5.0M  4.0K  5.0M   1% /run/lock
tmpfs                                    126G     0  126G   0% /sys/fs/cgroup
/dev/loop1                                65M   65M     0 100% /snap/gtk-common-themes/1514
/dev/loop2                                32M   32M     0 100% /snap/snapd/10707
/dev/sda2                                473M  141M  308M  32% /boot
/dev/loop0                               219M  219M     0 100% /snap/gnome-3-34-1804/66
/dev/loop4                                56M   56M     0 100% /snap/core18/1944
/dev/loop3                                98M   98M     0 100% /snap/core/10583
tmpfs                                     26G  4.0K   26G   1% /run/user/1000

Then it’s probably best to remove /run/netns, since it points to a nonexistent location anyway, and then try to update the lxd package (or snap in this case) again.

That worked:

$ sudo rm /run/netns
$ ls /run/netns
ls: cannot access '/run/netns': No such file or directory
$ sudo snap install lxd
lxd 4.10 from Canonical✓ installed