After some time without using a machine, I entered a snap source tree and:
$ snapcraft clean --use-lxd
internal error, please report: running "snapcraft" failed: cannot find installed snap "snapcraft" at revision 9542: missing file /snap/snapcraft/9542/meta/snap.yaml
So I tried reinstalling Snapcraft:
$ sudo snap refresh snapcraft
snap "snapcraft" has no updates available
$ sudo snap refresh --edge snapcraft
2023-09-14T14:03:38Z ERROR cannot remove snap file "snapcraft", will retry in 3 mins: umount: /snap/snapcraft/9510: not mounted.
2023-09-14T14:06:38Z ERROR cannot remove snap file "snapcraft", will retry in 3 mins: umount: /snap/snapcraft/9510: not mounted.
Of course the error would go on forever — I actually let the session sit and it ran for 15 h straight with the same error.
Snapd is from the stable channel.
==> /proc/self/mountinfo <==
23 28 0:21 / /sys rw,nosuid,nodev,noexec,relatime shared:7 - sysfs sysfs rw
24 28 0:22 / /proc rw,nosuid,nodev,noexec,relatime shared:12 - proc proc rw
25 28 0:5 / /dev rw,nosuid,relatime shared:2 - devtmpfs udev rw,size=8161852k,nr_inodes=2040463,mode=755,inode64
26 25 0:23 / /dev/pts rw,nosuid,noexec,relatime shared:3 - devpts devpts rw,gid=5,mode=620,ptmxmode=000
27 28 0:24 / /run rw,nosuid,nodev,noexec,relatime shared:5 - tmpfs tmpfs rw,size=1636684k,mode=755,inode64
28 1 252:1 / / rw,relatime shared:1 - ext4 /dev/vda1 rw,discard,errors=remount-ro,commit=30
29 23 0:6 / /sys/kernel/security rw,nosuid,nodev,noexec,relatime shared:8 - securityfs securityfs rw
30 25 0:25 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
31 27 0:26 / /run/lock rw,nosuid,nodev,noexec,relatime shared:6 - tmpfs tmpfs rw,size=5120k,inode64
32 23 0:27 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime shared:9 - cgroup2 cgroup2 rw
33 23 0:28 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime shared:10 - pstore pstore rw
34 23 0:29 / /sys/fs/bpf rw,nosuid,nodev,noexec,relatime shared:11 - bpf bpf rw,mode=700
36 24 0:30 / /proc/sys/fs/binfmt_misc rw,relatime shared:13 - autofs systemd-1 rw,fd=29,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=22511
37 25 0:31 / /dev/hugepages rw,relatime shared:14 - hugetlbfs hugetlbfs rw,pagesize=2M
38 25 0:19 / /dev/mqueue rw,nosuid,nodev,noexec,relatime shared:15 - mqueue mqueue rw
39 23 0:7 / /sys/kernel/debug rw,nosuid,nodev,noexec,relatime shared:16 - debugfs debugfs rw
40 23 0:12 / /sys/kernel/tracing rw,nosuid,nodev,noexec,relatime shared:17 - tracefs tracefs rw
41 23 0:32 / /sys/fs/fuse/connections rw,nosuid,nodev,noexec,relatime shared:18 - fusectl fusectl rw
42 23 0:20 / /sys/kernel/config rw,nosuid,nodev,noexec,relatime shared:19 - configfs configfs rw
65 27 0:33 / /run/credentials/systemd-sysctl.service ro,nosuid,nodev,noexec,relatime shared:20 - ramfs ramfs rw,mode=700
67 27 0:34 / /run/credentials/systemd-sysusers.service ro,nosuid,nodev,noexec,relatime shared:21 - ramfs ramfs rw,mode=700
69 27 0:35 / /run/credentials/systemd-tmpfiles-setup-dev.service ro,nosuid,nodev,noexec,relatime shared:22 - ramfs ramfs rw,mode=700
97 28 252:15 / /boot/efi rw,relatime shared:48 - vfat /dev/vda15 rw,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
100 28 7:1 / /snap/lxd/24918 ro,nodev,relatime shared:50 - squashfs /dev/loop1 ro,errors=continue,threads=single
135 27 0:36 / /run/credentials/systemd-tmpfiles-setup.service ro,nosuid,nodev,noexec,relatime shared:54 - ramfs ramfs rw,mode=700
106 36 0:37 / /proc/sys/fs/binfmt_misc rw,nosuid,nodev,noexec,relatime shared:56 - binfmt_misc binfmt_misc rw
313 27 0:24 /snapd/ns /run/snapd/ns rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,size=1636684k,mode=755,inode64
676 27 0:49 / /run/user/1000 rw,nosuid,nodev,relatime shared:189 - tmpfs tmpfs rw,size=1636680k,nr_inodes=409170,mode=700,uid=1000,gid=1000,inode64
548 28 7:3 / /snap/core20/1974 ro,nodev,relatime shared:188 - squashfs /dev/loop3 ro,errors=continue,threads=single
565 28 7:4 / /snap/snapcraft/9510 ro,nodev,relatime shared:295 - squashfs /dev/loop4 ro,errors=continue,threads=single
788 28 0:48 / /var/snap/lxd/common/ns rw,relatime - tmpfs tmpfs rw,size=1024k,mode=700,inode64
808 788 0:4 mnt:[4026532206] /var/snap/lxd/common/ns/shmounts rw - nsfs nsfs rw
767 788 0:4 mnt:[4026532258] /var/snap/lxd/common/ns/mntns rw - nsfs nsfs rw
1393 28 7:5 / /snap/snapd/19457 ro,nodev,relatime shared:378 - squashfs /dev/loop5 ro,errors=continue,threads=single
1494 28 7:6 / /snap/core22/817 ro,nodev,relatime shared:396 - squashfs /dev/loop6 ro,errors=continue,threads=single
314 28 7:7 / /snap/lxd/25112 ro,nodev,relatime shared:150 - squashfs /dev/loop7 ro,errors=continue,threads=single
365 313 0:4 mnt:[4026532203] /run/snapd/ns/lxd.mnt rw - nsfs nsfs rw
503 28 7:8 / /snap/core22/858 ro,nodev,relatime shared:184 - squashfs /dev/loop8 ro,errors=continue,threads=single
80 28 7:9 / /snap/snapcraft/9542 ro,nodev,relatime shared:32 - squashfs /dev/loop9 ro,errors=continue,threads=single
534 28 7:10 / /snap/core20/2015 ro,nodev,relatime shared:195 - squashfs /dev/loop10 ro,errors=continue,threads=single
714 28 7:11 / /snap/snapd/19993 ro,nodev,relatime shared:202 - squashfs /dev/loop11 ro,errors=continue,threads=single
111 27 0:38 / /run/credentials/systemd-resolved.service ro,nosuid,nodev,noexec,relatime shared:35 - ramfs ramfs rw,mode=700
47 28 252:1 /snap /snap rw,relatime shared:1 - ext4 /dev/vda1 rw,discard,errors=remount-ro,commit=30
60 47 7:12 / /snap/snapd/20092 ro,nodev,relatime shared:310 - squashfs /dev/loop12 ro,errors=continue,threads=single
63 28 7:12 / /snap/snapd/20092 ro,nodev,relatime shared:310 - squashfs /dev/loop12 ro,errors=continue,threads=single
How to proceed?