Possible ? - clean install but preserve one filesystem ?

[Matthew Seaman]

On Sat, Sep 13, 2003 at 09:38:44PM +1200, Richard Shea wrote:
> Hi - I'm having problems upgrading 4.4 -> 4.8 but it's got to work by
> Monday so I'm looking at all my options.
> 
> Before things went bad I backed up off the machine /etc and
> /usr/local/etc. Also took notes about file systems etc.
> 
> I have one file system on its own IDE drive that I would like to preserve
> and have available after the upgrade.
> 
> My question is this : if I act as if the machine had never had FreeBSD on
> it at all will a normal install in some way go digging around on that IDE
> drive  and trash the contents ? 
> 
> It doesn't seem likely but it's important that it's safe. 
> 
> If not I guess I could re-install from scratch and only once the install
> was complete would I then tell FreeBSD about the IDE drive ? It's a long
> time since I did a clean install and I've sort of forgotten the degree to
> which FreeBSD probes for disks.

You can certainly re-install FreeBSD on top of your previous
installation, and you can tell sysinstall not to wipe out any previous
contents of a partition.  You just need to be careful in the
'disklabel' screen to toggle the flag that says "don't newfs this
partition".  Disklabel will pick up the previous partition layout of
the drive, although you will have to fill in the mount points by hand.
If you need to take space from one partition to enlarge another, you
can, so long as you don't change the length or position of any
partitions you want to preserve.  Chances are you will want to do that
sort of thing, as the root partition in recent 4.x-STABLE needs more
like 128Mb nowadays, when at one point you used to be able to get away
with 32Mb.

If the stuff you want to preserve is on a separate drive, that makes
avoiding scribbling all over it even easier: you just tell sysinstall
that you only want to install on the other drive.

Once you've re-installed you'll need to rebuild all of the
customizations and re-install any ports you had previously, merge the
password and group files with the updated default versions, re-add the
partitions from your 2nd drive back into /etc/fstab and so forth.
It's not something that you can just grind through mechanically: you
will have to think about precisely what you're trying to achieve and
know the consequences of the commands you run.

In short, the answer is "Yes, it is possible, but you need to be
careful to avoid mistakes".

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP: http://www.infracaninophile.co.uk/pgpkey         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
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