Why has my UUID has changed?

Question

Level 1

20 points

Why has my UUID has changed?

I probably already have the answer to this question myself but I wanted to make sure, and also have a follow-up query based on the responses.

The system board was replaced last year after a nasty scrap between a cup of black coffee and my MBP (you will have immediately deduced who won).

Today I noticed that many of the plist and plist.lockfile files within my Library/Preferences/ByHost folder have duplicates, albeit with different UUIDs in the filename. The dates pretty much tie up with when the system board was replaced so my assumption is that the UUID changed with the new hardware.

Q1) Would someone be so kind as to verify my assumption, or make a loud raspberry if my assumption is erroneous?

On the basis that the response from our wonderful community is: "Your assumption is correct Livebox, you have not gone mad, and you may rest-assured that the world is at peace (for now)", my additional question(s) are:

Q2a) Is it safe to delete ALL plist and plist.lockfile files that sport the old UUID?

Q2b) Is it safe to delete ONLY those plist and plist.lockfile files that sport the old UUID AND have a new version that sports the new UUID?

I am renowned for for using language that is understood only by myself and a small section of the human race, so apologies if this is pure gibberish to the majority.

Regards to all.

MacBook Pro (17-inch Early 2008), Mac OS X (10.7.3), 4GB RAM - GeForce 8600M (512MB) GT

Posted on Mar 4, 2012 6:57 AM

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Answer 1

twtwtw

Level 5

4,948 points

Mar 4, 2012 8:21 AM in response to Livebox

First, what you're pointing at are not technically UUIDs. A UUID is a 128 bit string (alphanumeric characters in the format xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx). The strings in the ByHosts folder (which is in the user preferences, not the root-level preferences) look more like the locally unique tags generated by mktemp.

Most of the ByHost plists are not specific to hardware. For those that are, the change in file name probably does not refer directly to the hardware itself (hardware ids are generally kept within plist files, and are generally actual UUIDs). Most likely the file name randomness is part of an effort to write new files quickly without file system name conflicts.

Your deletion question has to be answered in 2 ways:

Safe? Probably. Plists the system needs will likely be regenerated if you delete them, and it's unlikely that the system needs to keep duplicates.
Wise? Probably not. Plist files are unassuming: unneeded plist files take up negligible space and are ignored by the system. You're weighing the (very small) benefit of regaining at most a couple of hundred kilobytes of disk space against the (very small) risk that you'll delete something which will make your system moan "oh woe is me!" and throw itself off a cliff.

If I were you I would use the following rubric:

Best to ignore it completely.
If you can't do #1, only delete files that have duplicates and are at least 3 months old.
Don't delete anything outright: move files to a folder somewhere and wait for a week to make sure nothing goofy happens. If goofiness happens, you can always put the file back.

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Answer 2

Linc Davis

Level 10

209,739 points

Mar 4, 2012 8:38 AM in response to Livebox

Yes, the UUID of the machine has changed. The property lists in the ByHosts folder are keyed to the UUID. Those with the old ID can be deleted without harm.

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Answer 3

Livebox Author

Level 1

20 points

Mar 5, 2012 8:13 AM in response to twtwtw

Thanks ever so much for the swift responses.

twtwtw: I warned you about my gibberish! To be more explicit, the plist filenames I'm referring to contain exactly the alphanumeric format you describe:

eg. com.apple.screensaver.175AB4C0-8D1A-5286-A6DF-4420A9145A3B.plist (old)

eg. com.apple.screensaver.73BCD19-0103-5819-B2AF-93FB12237B9D.plist (new)

(All alphanumeric characters appearing in the above are fictitious. Any resemblance to real characters, living or dead, is purely coincidental.)

When I checked my system information, the latter alphanumeric is listed under Hardware UUID.

All of the plist filenames in ByHosts contain one or the other of these alphanumerics. Nearly all of the former examples have modifications dates from around or before the time of the replacement board (Sept 2011 and earlier), and nearly all of the latter are after (Oct 2011 onwards). There are a few exceptions, and even a few that are dated Jan 2001 (on my early-2008 machine !?), but I've figured they're messing with my mind for a reason so will definitely leave them to their own devices just in case!

Your specific answer made me smile: "Safe? Probably. Wise? Probably not. Oh woe is me!" Classic!

You knew very well that I couldn't possibly bear the itch that Option 1 would give though, didn't you!?

Linc: Coupling your confident and authoritative words with twtwtw's safety net, your very different responses have yielded the same nett result!

I have very carefully adhered to Points 2 and 3, and a desktop folder now contains my old friends. After some time has passed without issue I will dispense with them.

One final note: it isn't the 'vast' memory return I'm looking for, and it isn't just being tidy either (although I am quite famously anal for that). No, it's the constant reminder that that UUID gives to the 20p cup of coffee that cost me £800 for a new system board and keyboard!

Thanks again to you both for providing all the information I needed to continue my recovery.

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Answer 4

twtwtw

Level 5

4,948 points

Mar 5, 2012 8:25 AM in response to Livebox

Livebox wrote:

You knew very well that I couldn't possibly bear the itch that Option 1 would give though, didn't you!?

No one ever can. That's what makes we humans so... err... special. 👿

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