Mount order for ZFS, jails, and nullfs

krad kraduk at
Fri Sep 24 18:15:43 UTC 2010

On 24 September 2010 17:03, Torbjorn Granlund <tg at> wrote:

> In jails, I'd like a local ZFS /, a read-only nullfs-mounted /usr, and a
> local /usr/local.  (I'd also have read-only nullfs-mounted /bin, /lib,
> /libexec, but let's forget about that for now.)
> This way, I can upgrade the master /usr once, in one place, and have all
> jails inherit it.  And my dear jail inmates can install anything in
> /usr/local (such as their favourite packages/ports).
> I.e., things should look like this:
> /myjail/                zfs
> /myjail/usr             nullfs ro
> /myjail/usr/local       zfs
> There is no problem to make this happen by issuing a handful of commands
> manually after boot, but I cannot seem to get it to work automatically,
> with existing boot mechanism.  The problem is that the mount of /usr
> will be attempted before ZFS has mounted /myjail, the jail's root.
> ZFS maintains its own mount table.  It is possible to disable the
> automated mounting in ZFS by specifying the pseudo mountpoint "legacy",
> and then--according to the FreeBSD manual--mount it with mount(8).
> Unfortunately, FreeBSD's mount seems unable to perform mounts of ZFS
> volumes.
> How can I achieve the result I want after a reboot?
> (The reply "use ezjail!" is not the right one.  :-) It does not do what
> I want to do.  I dislike its symlink forest, and that it creates just
> one ZFS filesystem for the entire jail.)
> --
> Torbjörn
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use zfs mount/imount

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