Stability of unionfs - general recommendation?

CyberLeo Kitsana cyberleo at
Sun Jun 8 18:16:03 UTC 2014

On 06/06/2014 03:35 AM, Matthias Petermann wrote:
> Hello,
> I'm planning a new server for the purpose of hosting multiple Jails.
> Each jail will get a dedicated UFS2 filesystem sourced from gvinum volumes.
> To make maintenance of the Jail base installation more efficient I consider
> to mount the dedicated filesystem(s) as an overlay above the base
> installation.
> Here is where unionfs comes into play as it provides these capabilities.
> My internet research yielded some questionable results on the stability of
> unionfs. I understood there was an "old" implementation and a "newer" one
> introduced in FreeBSD 6.3[1].
> Anyway - I'm curious if someone has a similiar setup running and can
> provide
> me some advice when to use unionfs and when not.
> Thanks in advance & kind regards,
> Matthias
> [1]

I use it extensively in jailed hosting on 9.x and 10.x, but only for
certain directories. It works perfectly fine for my use case.

To elaborate, I have a single prepared base tree null-mounted read-only
as root for each jail; upon this, things like /var, /home, and
/usr/local are null-mounted read-write from jail-specific directories,
as these are fully under control of the jail. I also have /etc mounted
from a jail-specific directory, as a union over the base /etc, because
the vast majority of the files in /etc will never be changed except upon
an upgrade, and everything else is changed solely by root.

To my knowledge, unionfs only seems to cause problems when permissions
come into play, or when you do things like running autotools on it, as
it does break certain critical expectations.

Fuzzy love,
Technical Administrator
CyberLeo.Net Webhosting
<CyberLeo at CyberLeo.Net>

Furry Peace! -

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