Important btrfs subvolumes like /root and /opt are unmounted during boot

[karlmistelberger]

@hcvv

I am not sure there is a Problem at all. The OP only reports that he sees those subvolumes as not mounted and that he can mount them with mount -a.
He does NOT report that things are not working because of unmounted sub-volumes.
He reports that at least one of them (/home) is mounted automatic when someone logs in. Thus normaly one would not detect that it was unmounted before that log in. I am now waiting on his report if login in as root also results in automatic mounting of /root. He can also try of course to do something inside /opt to see if automounting happens.

To me it looks like the automounting that formerly was (and still is) supported by /etc/automounter, but that now can also be used as a systemd feature (configurated directly in /etc/fstab). To me it looks as if systemd has one more “only do this when needed” feature. I admit that it is a bit of guessing, but the fact that /home is mounted when needed is the trigger for me.
When this automounting takes place, there is no problem, except that he is seeing a systemd feature at work.

systemd mounts what I need:

erlangen:~ # journalctl -b -o short-monotonic | grep -i mount
    0.142493] erlangen kernel: Mount-cache hash table entries: 65536 (order: 7, 524288 bytes, linear)
    0.142532] erlangen kernel: Mountpoint-cache hash table entries: 65536 (order: 7, 524288 bytes, linear)
    1.917314] erlangen systemd[1]: Condition check resulted in dracut pre-mount hook being skipped.
    2.866338] erlangen systemd[1]: Mounting /sysroot...
    2.877360] erlangen systemd[1]: Mounted /sysroot.
    2.977661] erlangen systemd[1]: Condition check resulted in dracut mount hook being skipped.
    3.837189] erlangen kernel: FAT-fs (sdb1): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
    3.853239] erlangen kernel: EXT4-fs (nvme0n1p3): mounted filesystem with ordered data mode. Opts: data=ordered
    4.060798] erlangen kernel: EXT4-fs (sda4): mounted filesystem with ordered data mode. Opts: (null)
    4.113867] erlangen systemd[1]: Mounting /home-HDD...
    4.113975] erlangen systemd[1]: Mounted /home-HDD.
erlangen:~ # 

Some of the following do not show up in journal:

erlangen:~ # mount |grep sdb5
/dev/sdb5 on / type btrfs (rw,relatime,ssd,space_cache,subvolid=576,subvol=/@/.snapshots/277/snapshot)
/dev/sdb5 on /.snapshots type btrfs (rw,relatime,ssd,space_cache,subvolid=266,subvol=/@/.snapshots)
/dev/sdb5 on /boot/grub2/i386-pc type btrfs (rw,relatime,ssd,space_cache,subvolid=265,subvol=/@/boot/grub2/i386-pc)
/dev/sdb5 on /boot/grub2/x86_64-efi type btrfs (rw,relatime,ssd,space_cache,subvolid=264,subvol=/@/boot/grub2/x86_64-efi)
/dev/sdb5 on /opt type btrfs (rw,relatime,ssd,space_cache,subvolid=263,subvol=/@/opt)
/dev/sdb5 on /srv type btrfs (rw,relatime,ssd,space_cache,subvolid=261,subvol=/@/srv)
/dev/sdb5 on /root type btrfs (rw,relatime,ssd,space_cache,subvolid=262,subvol=/@/root)
/dev/sdb5 on /usr/local type btrfs (rw,relatime,ssd,space_cache,subvolid=259,subvol=/@/usr/local)
/dev/sdb5 on /tmp type btrfs (rw,relatime,ssd,space_cache,subvolid=260,subvol=/@/tmp)
/dev/sdb5 on /var type btrfs (rw,relatime,ssd,space_cache,subvolid=258,subvol=/@/var)
erlangen:~ #