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Date:      Tue, 2 Sep 1997 11:01:07 +0930
From:      Greg Lehey <grog@lemis.com>
To:        Sara Gronim <sgronim@panix.com>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: Kernel question
Message-ID:  <19970902110107.09113@lemis.com>
In-Reply-To: <Pine.SUN.3.94.970901205500.27230C-100000@panix.com>; from Sara Gronim on Mon, Sep 01, 1997 at 08:56:42PM -0400
References:  <Pine.SUN.3.94.970901205500.27230C-100000@panix.com>

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On Mon, Sep 01, 1997 at 08:56:42PM -0400, Sara Gronim wrote:
> Hi, this is my first time writing to this service.
>
> Can i leave my generice kernel in place, build a new custom kernel and
> then implemenet the new kernel at the boot prompt? 

Yes.

> Is this possible, smart or in any way less risky than implementing
> the new kernel and keeping a copy of the old one?

No.  It's pretty much the same thing.

To understand why, you need to understand what the Boot: prompt does.
When, it appears, it gives you about 5 seconds to enter something.  If
you don't, it'll try to boot the file /kernel from its default
partition, normally /dev/sd0a (SCSI) or /dev/wd0a (IDE).

If you install a custom kernel, you have the choice of renaming the
old one, say, /kernel.GENERIC, and installing the new kernel as
/kernel.  Or you can leave the generic kernel where it is, and install
the new kernel as, say, /kernel.ALLMINE.  In either case, if you want
to boot the kernel not called /kernel, you just enter its name at the
Boot: prompt.  Obviously, it's better to name the kernel you use more
often /kernel.

Having said that, there are some problems involved with multiple
kernels.  Some of the programs in /sbin and /usr/sbin are sensitive to
the version of the kernel.  ps, in particular, will often not work
with a kernel of a different version.  On the other hand, you
shouldn't see any problems with kernels built from the same version
but with different config files.

Greg





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