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Assuming hardware failure is not a factor, and the requirement of being able to update periodically, is it possible to never shutdown Linux?

I typically do a full reboot after updates, especially kernel updates, but is there a way to keep my machine on and still do these? People always hear about incredible up-time, but how is that really possible if you must reboot after major updates.

Maybe a different run level? But then how would the kernel update kick in?

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    See also: ksplice, pannus.
    – jscott
    Apr 7, 2013 at 10:52
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    "Incredible uptime" is a synonym for "my box is begging to be compromised, if it's not already." As your question implies, those machines with incredible uptimes generally haven't been patched. Apr 9, 2013 at 16:17

2 Answers 2

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Server/Box "uptime" is an illusion. Unless your objective is to have incredible uptime in order to prove some kind of point then I wouldn't focus on it.

What matters is service availability. If you need a service to be available all the time then it might be useful to improve individual system uptime or it may well be simpler and more cost effective to create a cluster, for example, than to try and take the availability of a commodity server from 99% to 99.999%

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    +1 Couldn't agree more. The idea that individual box reliability should be related to service availability and reliability is a fallacy.
    – Dan
    Apr 7, 2013 at 16:18
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    Good work not answering the question. Why is this even the accepted answer? It should be downvoted for taking a detour. At the very least you should have tacked your current answer onto something that actually explains if OP's question is possible or not.
    – atx
    Apr 8, 2013 at 8:05
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    @atx feel free to downvote me if you wish - it's the accepted answer because the OP accepted it. And yes, I didn't address the question in the title because I instead chose to address the point about up-time in the question body. After all, Alojz's answer addresses the other points quite well and it would be senseless to duplicate their post.
    – Rob Moir
    Apr 8, 2013 at 12:57
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    @RobM Ah, fair enough then. I didn't look at his post.
    – atx
    Apr 9, 2013 at 0:07
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A standard linux is not designed to do this. It tries to minimze the reboots, but on some updates, like switching the kernel, reboot may be required.

There are projects that aim to also avoid this. See http://www.ksplice.com/ - now Oracle.

For live patching there is pannus, see http://lists.linux-foundation.org/pipermail/live_patching/attachments/20050725/14611ec4/050726pannus_latest.pdf

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