zfs-import-cache.service fails when using ZFS as root partition

[Daniel GALAMBOS]

When using ubuntu 18.04 with ZFS pool that used as the root filesystem is imported by initramfs, so the systemd job can't import that pool as it's already imported.

root@worker02:~# systemctl status zfs-import-cache.service
● zfs-import-cache.service - Import ZFS pools by cache file
   Loaded: loaded (/lib/systemd/system/zfs-import-cache.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Wed 2018-08-08 08:36:22 CEST; 2h 45min ago
     Docs: man:zpool(8)
  Process: 4044 ExecStart=/sbin/zpool import -c /etc/zfs/zpool.cache -aN (code=exited, status=1/FAILURE)
 Main PID: 4044 (code=exited, status=1/FAILURE)

aug 08 08:36:22 worker02 systemd[1]: Starting Import ZFS pools by cache file...
aug 08 08:36:22 worker02 zpool[4044]: cannot import 'rpool': pool already exists
aug 08 08:36:22 worker02 systemd[1]: zfs-import-cache.service: Main process exited, code=exited, status=1/FAILURE
aug 08 08:36:22 worker02 systemd[1]: zfs-import-cache.service: Failed with result 'exit-code'.
aug 08 08:36:22 worker02 systemd[1]: Failed to start Import ZFS pools by cache file.

[Andrea Righi (arighi)]

If I'm not wrong ZFS on root support has been introduced officially from 19.10 (eoan). I'm not sure if this one is still relevant, but with 20.04 I can't reproduce any errors/issues using ZFS as root and zfs-import-cache.service is working just fine.

If you are still experiencing this problem, can you provide more details? Did you configure ZFS as root filesystem manually? Which steps did you follow?

Otherwise I think we can close this one. Thanks.