Q: My iMac's computer name keeps changing automatically after Yosemite upgrade

It's doing it again...as soon as I switched networks.

Yup...changing again here too...oh well.

So, on to the next one!  At least I reclaimed a ton of disk space!

Mine is doing this 2, we had any updates on this?

I should have mentioned, I'm switching from wifi to wireless.

Good that at least you reclaimed disk space!

It's easy to forget these system health housekeeping should be performed occasionally (there are apps to do that).

So far, the rename is holding on both my machines. Have not switched wifi networks. I will be this afternoon. We'll see then!

In any case, the behaviour is an obvious bug Apple must address permanently, so hopefully everyone is submitting feedback.

I'm having this same issue as well.  Sure would like to get this resolved because it's very annoying!

Same problem here. I upgraded to Yosemite today, I have a (3) after my MacBooks name...it was (2) an hour ago. Example "My Mac (3)".

I have a  2012 MacBook Air. No matter what I do I can't get rid of the number.

You can try:

In Preferences > Energy Saver > deselect Wake for network access.

The fact remains this issue was not present in Mavericks for the most part (I never experienced it on the many Macs I manage), so it would seem a pesky Yosemite bug.

I have had this problem too. Renaming the computer 'cured' the original trouble I was having of using iSyncr to sync my music with my 'phone.

To prevent it from renaming itself again, I turned off the wake for LAN option in System Preferences / Sharing.

Job done I thought.

I then found that my Time Machine backups were all mixed up and inaccessible. If I renamed the computer to 'iMac (2)' and entered Time Machine some backups were present, others were not. If I named it the original 'iMac' other backup versions became visible, some not.

At this point, I wiped my Time Machine and started it again.

Job done I thought.

Next problem was that I was looking for an email that I knew I'd had, but couldn't remember when. I tried searching for it in Mail but no results were returned. I tried shorter and shorter search terms until I eventually realised Mail wasn't searching at all. I tried rebuilding the Mail indexes and various other things but still no search results.

I tried a Spotlight search. Nothing. No results for anything typed. I then tried all manner of things to turn off Spotlight (one of which was dropping the drive into the Privacy window) and after a number of fruitless attempts resulting in various error messages, I eventually found this: http://www.sciencemedianetwork.org/Blog/20130321_Spotlight_fix which after a few attempts and a restart did start the Spotlight indexing again and finally, searching in Mail returned the email I was looking for.

Job done?

I hope so.

I saw the same problem on my MPB after installing Yosemite - the Computer name changed 'magically' to "(2)" or "(3)" and so on.

In Yosemite, there is a new option in the Sharing panel:

File Sharing ON => Options

=> Share files an folders using SMB **or**

=> Share files an folders using AFP

(SMB means Samba, AFP means Apple Filesharing Protocol)

In my case, I got rid of the Computer name change problem by disabling the SMB option.

I think that automatic mounting of the Computer (the HD share) from other Macs/PCs in a home network triggers the Computer name change problem.

Could be a contributing factor, or coincidental.

Those sharing options are disabled by default (all sharing is off), and I have never shared any of my Mac drives.

The auto renaming was an issue on my systems with Yosemite.

However, since I followed the steps I posted earlier (repairing permissions), including disabling Wake for network access, there have been no instances of auto renaming, for a few days now.

Long may it stick!

Still the same here happening on all of my 3 Macs on Yosemite (never before under Mavericks, and before.).

None of the proposed tricks helped. Resetting the host name in preferences > sharing helps for a while but suddenly after some hours or days hostname iterations appear again (2), (3), etc. on all machines in my LAN.

Not using 'back to my mac' on any machine ever.

It really drives me nuts here!

To disable this behavior on Yosemite you can do it by running following command and reboot:

sudo /usr/libexec/PlistBuddy -c "Add :ProgramArguments: string --no-namechange" /System/Library/LaunchDaemons/com.apple.discoveryd.plist

As seen on: http://ispire.me/fix-yosemite-rtc-alarm-wakeup-issue/

fixed mine and all the problems i was having with Sonos!

I followed your steps, with the addition of unchecking, "Wake For Network Access"  under Energy Save (Preferences).  It has been over 24 hours since I did this, and so far, so good!