I noticed this the other day, and thought it was interesting.
When the jailed property is set on a ZFS fileset, it affects the mountpoint within the jail.
If your jail uses allow.mount.zfs (known as allow_mount_zfs when using iocage), the mountpoints become relative to the jail.
For example, in my poudriere jail, this is what I see the main dataset:
[dan@pkg01:~] $ zfs list tank_fast/poudriere NAME USED AVAIL REFER MOUNTPOINT tank_fast/poudriere 51.1G 452G 88K /usr/local/poudriere [dan@pkg01:~] $
From the host, this is what I see:
[dan@r720-01:~] $ zfs list tank_fast/poudriere NAME USED AVAIL REFER MOUNTPOINT tank_fast/poudriere 51.1G 452G 88K /usr/local/poudriere [dan@r720-01:~] $
That is exactly the same thing.
Let’s look at the mountpoint within the jail:
[dan@pkg01:~] $ zfs get mountpoint tank_fast/poudriere NAME PROPERTY VALUE SOURCE tank_fast/poudriere mountpoint /usr/local/poudriere local
Yep, that is where is should be.
I expected the host to show the same thing, and that some magic was occurring under the hood.
Yeah, precisely the same thing on the host:
[dan@r720-01:~] $ zfs get mountpoint tank_fast/poudriere NAME PROPERTY VALUE SOURCE tank_fast/poudriere mountpoint /usr/local/poudriere local
So where is the magic? Something has to be mounting the filesets into the jail?
The magic isn’t in the definde mountpoints, it’s what zfs does when it performs the mount.
It can be seen here, on the host:
[dan@r720-01:~] $ zfs mount | grep tank_fast/poudriere tank_fast/poudriere /iocage/jails/pkg01/root/usr/local/poudriere
I have trimmed the output to include only the top level.
The path to the jail has been prepended to the mountpoint.
You can find the path with this command:
[dan@r720-01:~] $ jls -n -j 11 path path=/iocage/jails/pkg01/root
Where 13 is the jail id of your jail.
