IPU's vs. Fresh Installs

In-Place OS Upgrades can ruin your day. I'm not talking about complete failures that trash your system: obviously you made backups and can start over in that case.

No, what I'm talking about is upgrades that appear to be succesful, but have introduced subtle (or not so subtle) problems that can be devilishly hard to resolve.

IPU's of course attempt to preserve previous configuration information. That's the whole point. But sometimes you don't WANT the previous setup. Driver information may be incorrect, configuration file settings may not apply and so on. Some of that will be caught by the IPU, but no amount of engineering foresight will ever catch everything.

Actually, if an IPU produced a list of files it preserved from the old system, I could work from that direction. I'd want a diff listing of all system directories so I could see files that would NOT have been there with a fresh install, and a diff for any system file that would have been put down new but was preserved or merged. If I had that, IPU's would be neat.

Maybe what I want IS there: see /Bofcusm/2287.html

But they don't give me that, so my approach is always to install new, and then to restore everything from the old system to a separate directory where files can be examined. It's not hard to write scripts to find what is different, and you can then quickly put in place the old settings that you really do want.

This is actually often quicker than doing an IPU. The fresh install is very much quicker, and it takes very little time to identify changes needed.

You'll want to look for:

• Directories that don't exist in the new hierarchy. Usually you can just move these over. The only time you need to be careful is when they are in system directories. Those need to be examined. In other instances, this finds things you don't need or want any more. Good time to get rid of them.
• After looking at directories, and moving what is appropriate, you need to look for files that aren't in the new hierarchy. These can be a source of trouble, so look at these carefully before moving them over.
• Files that do exist in the new system but have different contents. Sometimes you can just copy these over, but do a diff first: there may be new configuration information in the new files that shouldn't be overwritten, or in some cases you don't want to do anything.

Document and archive anything you do not entirely understand. If you are merging or copying files from the old system, save a diff of what you are doing against the virgin file put down by the fresh install if you have any doubts about why you are making the changes. This lets you go back to the (hopefully) stable fresh install configuration if it becomes necessary or if you suspect a problem.

References:

Upgrades
IPU vs. Fresh Install
IPU vs. Fresh Install
IPU vs. Fresh Install Opinion Poll

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