an OS question

[cellio]

While waiting for assorted software updates to install today I found myself wondering... Mac OS and Windows usually need to reboot your machine to install updates. Yet I have, several times, seen Unix machines that I believe were being maintained with uptimes of more than a year. What's the deal? Is Unix just better able to support hot-fixes, or are Unix updates that rare? (Or am I wrong about the maintenance of those machines?) And if it's that Unix is better at updating, why does Mac OS, which is Unix-based, need to reboot so often? Mind, it's definitely better in this regard than when I was running Windows; this is a puzzle, not a rant.

Edit: Thanks for the comments thus far. I now understand more about how Unix is put together, and why Windows is different. Still not sure about Mac OS but comments suggest it could be UI-related (that is, the GUI might be more tied into the OS than is the case on Unix).

Comments

[brokengoose.livejournal.com]

Some mission-critical Unix systems can be hotpatched, too -- even kernels. (See ksplice for Linux for one example).

It's a hassle, and it can bite you later during the "see if it reboots cleanly" stage of your next maintenance window, but it can be useful if availability really matters.

(This can mean, in some environments, that development or QA servers are hotpatched, too, so that they mirror the production servers as closely as possible.)

[rjmccall.livejournal.com]

Neat. ksplice looks to be relatively heavyweight compared to MS hotpatching, since it requires briefly halting everything except ksplice; but I doubt it makes much difference in practice; the length of actual downtime should be brief unless it actually needs to update data structures, which is not something MS's hotpatching makes any easier.