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From: Arthur Chance <freebsd@qeng-ho.org>
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To: Victor Sudakov <vas@mpeks.tomsk.su>, freebsd-questions@freebsd.org
Subject: Re: /etc on a separate filesystem ?
References: <20140904150739.GA42707@admin.sibptus.tomsk.ru>
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On 04/09/2014 16:07, Victor Sudakov wrote:
> Colleagues,
>
> Is it possible to keep /etc on a separate filesystem?
>

Lots of people have already pointed out that /etc/fstab is need to mount 
all file systems other than /.

However, the answer is actually yes, if you are prepared to do a bit of 
work, and you can do it within the standard FBSD framework. nanobsd is 
an example of this, as is pfSense (or at least the embedded version I run).

The magic happens by creating /etc/diskless, which causes /etc/rc to 
source /etc/initdiskless before doing any other rc work. This was 
intended for diskless machines which mount their file systems via NFS, 
but can be (ab)used for other purposes.

I suggest you take a look at /etc/initdiskless, which has documentation 
as a comment near the beginning, and possibly 
/usr/src/tools/tools/nanobsd/nanobsd.sh which builds FBSD for appliances.

Be warned that this isn't something for the inexperienced user.