RE: Live Upgrade for Linux
From: Rohan, Daniel G. (DRohan@anl.gov)
Date: Wed, 26 Mar 2003 14:29:50 -0600 From: "Rohan, Daniel G." <DRohan@anl.gov> To: "Kelly Sauke" <email@example.com>
What I have done on some critical servers is create a /alt_root under
which I do a dump piped to a restore into this directory. I then
patch/upgrade my system leaving this directory alone. I then adjust the
file /alt_root/etc/fstab to the correct device parameters. Then, if
something goes wrong, then I can simply change my 'root' kernel
parameter in grub or lilo and boot off of the original partition.
As a technical detail, I believe that you could even use the same /boot
partition; this partition does not change radically in upgrades, and
should be usable as long as the old kernels and initrd images were
saved. I cannot verify this because I usually have not created /boot
partitions. Silly me.
> Its a complete boot environment copy that you can do anything
> to and then just reboot off the new environment without having to
> the 'live' environment.
As far as the ability to do an upgrade to an alternate directory tree
while leaving the existing running environment stable...I don't think it
exists in the linux world. Please let me know if it does.
Daniel G. Rohan
Argonne National Laboratory
Maybe I need a little clarification of what Live Upgrade does. I've
gotten a lot of response of what I would call installer utilities but
not a Live Upgrade (if I'm wrong please point it out to me). What Live
Upgrade does under solaris is it creates a complete alternate boot
environment with a root /usr /var and any other filesystem you want.
Then you can apply patches etc to this other boot environment and boot
off of that. If there is something in the patch that doesn't work or
screws up the machine, then you just reboot off the original boot
environment and you're back to where you were before upgrading and still
have access to the patched boot environment to fix it. Its great for
upgrading production type servers because the 'back out plan' if you
will is nothing more than reboot off the old boot environment. In other
words you have 2 / filesystems, 2 /usr's, 2 /var's as well as 2
kernels. Its a complete boot environment copy that you can do anything
to and then just reboot off the new environment without having to touch
the 'live' environment.
For those that were asking, I'm running RedHat Advanced Server. I
appreciate the responses.
Kelly Sauke wrote:
> Does anyone know of any software for linux that acts similar to "Live
> Upgrade" in Solaris or "Alternate Release Areas" in DG/UX?
> I would find it very useful for upgrading and patching as well as
> security audits to the applied OS "patches".