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Date:      Wed, 9 Feb 2000 09:40:06 +0100 (CET)
From:      Oliver Fromme <olli@dorifer.heim3.tu-clausthal.de>
To:        freebsd-questions@FreeBSD.ORG
Subject:   Re: memory filesystem
Message-ID:  <200002090840.JAA49968@dorifer.heim3.tu-clausthal.de>
In-Reply-To: <877803$2ot7$1@atlantis.rz.tu-clausthal.de>

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Chad David <davidc@guild.ab.ca> wrote in list.freebsd-questions:
 > I have a need to create a memory filesystem
 > on a system that boots from a CD.  That means
 > that besides a floppy, I have no writable media,
 > and therefore, no swap.
 > [...]
 > and MFS seems to require a writable block device.

Such as /dev/zero.  :-)

The only thing mfs_mount needs a device for is to find out the
disk type and size of the partition.  If you specify the size
with -s and the disk type with -T (which can be any entry from
your /etc/disktab, such as "minimum" which is always present),
then you can simply use /dev/zero as device.  It will simply
be ignored by mount_mfs.

So, for example, your /etc/fstab entry could look like this:

/dev/zero  /tmp  mfs  rw,nosuid,-s=64000,-m=0,-T=minimum  0  0

We're using the above entry on our diskless websurf terminals,
which mount the whole system read-only via NFS, so we need a
small writable MFS for a few things, too.  Works great.

Regards
   Oliver

-- 
Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany
(Info: finger userinfo:olli@dorifer.heim3.tu-clausthal.de)

"In jedem Stück Kohle wartet ein Diamant auf seine Geburt"
                                         (Terry Pratchett)


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