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.As exactly described: No. There is no well-known tool that creates a complete "mirror" system for the sole purpose of isolating upgrades. Can it be done: Yes. There's nothing that stops you from replicating a root volume to an unused drive, applying patches, and changing the bootloader to offer the new kernel/filesystem combo as the default, while still listing the orginal.
If you are strictly talking about kernel upgrades, Red Hat will keep the kernel image and the loadable modules unless you choose to remove them. It's not unusual to have 2-3 kernel versions on the same filesystem after multiple kernel releases; to get back to a specific setup, just select a different kernel at boottime through the bootloader, and to make it the default, once you have completed the reboot you would apply a change to the bootloader config and reapply the bootloader. I have no less than 3 kernel setups on my RH7.1 box, which include the original off-the-CD kernel, a uniprocessor upgraded kernel, and an SMP-ready kernel which is set to load by default. (The machine is behind a physically secure door, so I don't worry about someone breaking in and using an older kernel image).
