Re: canmount=noauto not behaving as expected

Am Thu, 27 Apr 2023 15:54:49 +0200
schrieb Gerrit Kühn <gerrit.kuehn@aei.mpg.de>:

> However, I still don't get any of the nested filesystems mounted on
> "zpool import", they all stay unmounted there. So canmount is (quite
> unexpectedly to me) treated differently for "zpool import" and "zfs
> mount -a".

More precisely:

---
root@crest:/etc # zfs get canmount data/syncoid/pt-vault
NAME                   PROPERTY  VALUE     SOURCE
data/syncoid/pt-vault  canmount  on        default

root@crest:/etc # zfs get canmount data/syncoid/pt-vault/home
NAME                        PROPERTY  VALUE     SOURCE
data/syncoid/pt-vault/home  canmount  noauto    local

root@crest:/etc # zfs get canmount data/syncoid/pt-vault/home/archives
NAME                                 PROPERTY  VALUE     SOURCE
data/syncoid/pt-vault/home/archives  canmount  on        default
---

So canmount=noauto is just set for one filesystem "in the middle", not for
the one above, nor for the one below.

---
root@crest:/etc # zfs mount -a

root@crest:/etc # zfs get mounted data/syncoid/pt-vault
NAME                   PROPERTY  VALUE    SOURCE
data/syncoid/pt-vault  mounted   yes      -

root@crest:/etc # zfs get mounted data/syncoid/pt-vault/home
NAME                        PROPERTY  VALUE    SOURCE
data/syncoid/pt-vault/home  mounted   no       -

root@crest:/etc # zfs get mounted data/syncoid/pt-vault/home/archives
NAME                                 PROPERTY  VALUE    SOURCE
data/syncoid/pt-vault/home/archives  mounted   yes      -
---


After a "zfs mount -a" only the filesystem that is explicitely set to
"noauto" will be left out, the ones below will still mount. I didn't
really expect this, but so be it.

However, what I find really strange now is that "zpool import" behaves
differently:

---
root@crest:/etc # zpool export data
root@crest:/etc # zpool import data
root@crest:/etc # zfs get mounted data/syncoid/pt-vault/home/archives
NAME                                 PROPERTY  VALUE    SOURCE
data/syncoid/pt-vault/home/archives  mounted   no       -
root@crest:/etc # zfs get mounted data/syncoid/pt-vault/home
NAME                        PROPERTY  VALUE    SOURCE
data/syncoid/pt-vault/home  mounted   no       -
---


Importing appears to stop right at the level where canmount=noauto is set
and does not consider the filesystems below. The zfsprops manpage doesn't
comment on this situation explicitely, but from this I would have expected
that import and mount are treated the same way:

---
       When set to noauto, a dataset can only be mounted and unmounted
       explicitly.  The dataset is not mounted automatically when the
       dataset is created or imported, nor is it mounted by the zfs mount
       -a command or unmounted by the zfs unmount -a command.
---


Maybe the manpage could be improved here to mention this? The manpage for
zpool-import also doesn't mention which filesystems are mounted
automatically and which ones aren't (it just features the -N flag that
prevents any filesystems from being mounted).


cu
  Gerrit