Originally posted by Marvin
It would be a part of the system where each system update is installed in such a way that it can be rolled back.
Which requires an assembly of all files and changes (e.g. permission changes) performed by that system update.
Which requires cooperation from the installer.
For example, let's say OS X needs component x. Then all it would do is have an alias to that component. An update would update the alias but the system would keep note of the change and it could be reverted back to the old link if needed.
That works for files, but not for more complex changes. For example, running shell scripts cannot easily be rolled back at all; certainly not through aliases.
I'm not sure how a backup would help him restore his system anyway. Surely a backup would replace all his files too. [/B]
Well, that's the point.
If you're worried that a system update messes up your system (never happened to me, but it sure is possible), and if you don't have time to manually restore things, simply:
2) install the update
3a) cheer if things work out
3b) restore the backup if they don't, and forget about the update for the time being.