Re: Live Upgrade for Linux

From: Christopher Cashell (topher@zyp.org)
Date: 03/28/03 

Date: Thu, 27 Mar 2003 21:43:20 -0600
From: Christopher Cashell <topher@zyp.org>
To: focus-linux@securityfocus.com

At Wed, 26 Mar 03, Unidentified Flying Banana Eric Rostetter, said:
> This isn't the same as Live Upgrade. With Live Upgrade, I can install a
> fresh OS while the machine is running, or upgrade (e.g. From Solaris 8
> to Solaris 9) while the system is running. In the linux world, at least
> the versions I've used, you can't do this (Install RedHat 8.0 on the
> machine while it is up and running RedHat 7.3, or upgrade 7.3 to 8.0
> while running). In other words, there are no vendor install/upgrade
> utilities that I know of for linux that run on a running system.

I will state first of all that I have very limited familiarity with Live
Upgrade, and I don't know of any "complete solution" available for Linux
that can provide all of it's functionality.

However, at least one Distribution can be upgraded from one version to
another without rebooting, and while the system is running. Debian does
provide this capability. Upgrading from, for example, Debian 2.2 Potato
to Debian 3.0 Woody can be done with a simple change to
/etc/sources.list, and running 'apt-get update && apt-get dist-upgrade'.

This will go through and upgrade all the installed software on live
running machine, without need for a reboot or running a special
installer utility/CD.

> I agree you can do updates (install security patches, etc) this way.
> But not a full install or major OS upgrade, AFAIK.

A full install would be somewhat trickier, though with a little work, it
should be doable. A major OS upgrade is definitely possible, but you
should be prepared for possible minor down time while individual
applications are upgraded.

> The alternative I use, and it sucks, is:
>
> Software mirror the disks. Break the mirror. Move the drive to another
> machine which has the exact same hardware. Do the upgrade/install. Shut
> down the first machine. Swap the disks. Boot. Once it all works, is
> tested, etc. then resync the mirrors. If it fails, reboot off the old
> (not yet synced) disk.
>
> Problem is obvious: it requires another machine of the same type of hardware.

Someone else mentioned User Mode Linux. Combining UML with a chroot for
your upgrade or new install might be a feasible way to achieve what
you're looking for. It would likely require some work though, and would
not be as slick or easy to use as Solaris's Live Upgrade sounds to be.

> --
> Eric Rostetter 

-- 
| Christopher
+------------------------------------------------+
| A: No.                                         |
| Q: Should I include quotations after my reply? |
+------------------------------------------------+

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