Posted Aug 8, 2010 12:33 UTC (Sun) by nix
In reply to: real world?
Parent article: Realtime Linux: academia v. reality
With glibc (or with any other user-space library) there is no such multi-version capability: if the glibc upgrade went wrong and even /bin/ls is segfaulting then it's game over and you are on to a difficult and non-standard system recovery job.
Though a copy of sash helps immensely there.
xorg is pretty easy to upgrade and downgrade actually because its shared library versioning is so strictly maintained. If you downgrade a really long way you might get burnt by the Xi1 -> Xi2 transition or the loss of the Render extension, but that's about all.
The kernel is particularly easy to upgrade *if you run the system and can reboot it on demand* (which is a good thing given the number of security holes it has!), but if both of those conditions are not true it is nearly impossible to upgrade. (Let's leave out of this the huge number of people running RHEL systems who think they're forbidden from upgrading the kernel by their support contract, even though they aren't...)
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