Upgrading Red Hat (Alpha & Intel) w/o rebooting

Donald Becker becker at scyld.com
Thu Jul 6 14:25:19 PDT 2000

On Thu, 6 Jul 2000, Philip E. Varner wrote:

> > In general, how would Debian/FreeBSD get around getting the
> > new kernel running without a reboot? Also, updates to things
> > like libc are problematic without rebooting.
> The problem was not rebooting itself.  The problem is rebooting _with a
> floppy disk_, as is required by Red Hat's installer.  If the floppy drive

This isn't exactly the same situation, but we faced a similar situation when
designing the booting system for our new Beowulf distribution.  With our
"generation 2" Beowulf system we substitute kernels without going through a
warm boot using "Two Kernel Monte".

This allows us to start up the system with a minimal kernel that only knows
about RAM-based filesystems and network adapters.  (It knows about almost
every type of network adapter!)  For the first stage we have a mini-libc,
not the (monstrously large) full version.

We then substitute a full kernel with BProc support, still running off of
a RAM filesystem.  This second stage kernel loads all of its kernel
modules from the RAM disk, and starts accepting BProc commands from
whichever front-end wants to configure it.  All this takes place without
touching a disk, so the initial install, a checkpoint recovery, and a
regular boot all are exactly the same, with the behavior controlled by
either a script or GUI on the front-end.

Finally we reconfigure the kernel to mount swap space and the remount the
final root and other run-time filesystems, and the machine starts acting as
a normal cluster slave node.

The point is that, if you are clever enough, you never have to go through
the PC warm-reboot sequence, even for upgrading the kernel and/or
libraries.  (You do have to shut down all running processes, but you must do
that for any kernel or library change.)

A final note: Two Kernel Monte isn't Beowulf-kernel specific.  It doesn't
even require adding kernel hooks.  It's designed to work with a generic
kernel, such as an out-of-the-box Red Hat or Turbo kernel.

Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Beowulf Clusters / Linux Installations
Annapolis MD 21403

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