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Date: Mon, 22 Sep 2008 09:23:08 +0200 (CEST)
From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Matt Fioravante <fmatthew5876@gmail.com>
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Cc: freebsd-questions@freebsd.org
Subject: Re: Shared /usr in jails
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> I want to implement a number of jails for different services on a single
> box.
>
> Since /usr is the same everywhere I'd like to just mount one copy of it
> read-only to all the jails and then have them each have their own /usr/local

well - i already do this, but both /usr and /usr/local are common

simply install in /usr/local everything all jail users needs.


> Someone recommended keeping the main system's /usr separate. This would mean
> building a /usr for the main system and then making a copy of it
> to be shared by the jails.
>
> Aesthetics and philosophy aside, are there any real security holes in just
> using the systems /usr everywhere if it is mounted read only in the jails?

no it works fine AND saves memory, all binaries are shared

use mount_nullfs -o readonly for this.

link /usr/local/etc to for example /etc/local so configs can be different 
in every jail