Newbie Question About System Update

[Karl Denninger]

On Tue, Apr 19, 2005 at 02:02:04PM -0700, Kent Stewart wrote:
> On Tuesday 19 April 2005 01:39 pm, Dan Nelson wrote:
> > In the last episode (Apr 19), Bill Moran said:
> > > Chuck Swiger <cswiger at mac.com> wrote:
> > > > Bill Moran wrote:
> > > > > The system can not replace programs that are in use,
> > > >
> > > > This is generally not the case.  Unix lets you continue to access
> > > > a file after it has been deleted, so long as the process hangs on
> > > > to a file descriptor.  This lets you replace programs in use,
> > > > without running into the same problems that platforms like
> > > > Windows have.
> > >
> > > What you say?:
> > >
> > > bash-2.05b$ su
> > > Password:
> > > bolivia# cp /usr/sbin/cron /home/wmoran/.
> > > bolivia# cp /home/wmoran/cron /usr/sbin/.
> > > cp: /usr/sbin/./cron: Text file busy
> > > bolivia#
> > >
> > > Notice that /usr/sbin/cron is in use (because my system is running
> > > normally)  I can copy _from_ that file, but I can not overwrite it.
> >
> > What you can do, however, is: create the new file under a temporary
> > name, delete the original, and rename the temp file to the orignal's
> > name, which is what /usr/bin/install does.  I've done many
> > installworlds on running systems without problems.
> 
> You are forgetting that one of the real purposes of the boot -s is to 
> test your new kernel. If you have never been bitten by a kernel that 
> would only panic, you have no problems. If you have, you know that you 
> can boot the old kernel and continue without any problems until some 
> one solves the panic. You will not most likely hit that situation on a 
> security based version but this is freebsd-stable and it can happen at 
> any time. 
> 
> My attitude is that if you don't boot -s, you are simply playing 
> Russian-roulette with your system. Some day, it will bite you.
> 
> Kent

Not if your update procedure saves the old kernel.

Yes, you will have to get there to recover.  You have to get there (either 
physically or serial console) anyway if it blows up on you.

The old kernel (and loadables for it) should ALWAYS be saved when updating
"in place", lest you discover exactly what you're warning about the hard way.

--
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