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Why did my local hostname suddenly change?

#1 User is offline   dcamp 

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Posted 24 May 2008 - 06:15 AM

I have been using OS X Leopard (10.5.2) for several months on my home Mac with no problems. The Mac has two user accounts, one for me and one for my wife. It is not networked with other computers, but it does have an external hard drive for Time Machine to archive changed files and it is connected to my ISP via a high-speed cable modem. The Mac is left running 24/7 and allowed to "sleep" when not in use. Yesterday when I woke up the Mac, a dialog box popped up unexpectedly that said: "This computer's local hostname 'Macintosh.local' is already in use on this network. The name has been changed to 'Macintosh-2.local'. To change the local host name, open System Preferences and click Sharing, then click 'Edit' and change the name." I did change the name back to "Macintosh.local" and continued to use the Mac to check mail and surf the Web, then I let it sleep. This morning, the same message appeared in a dialog box when I woke up the Mac. Why? What is changing the local hostname in the background? Have I been hacked or do I have a virus? What is happening?
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#2 User is offline   MacosNerd 

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Posted 24 May 2008 - 07:54 AM

That message is indicitive of when another Macintosh computer is on the network. Are you running a wireless network, or is the computer plugged directly into the the cable modem
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#3 User is offline   dcamp 

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Posted 26 May 2008 - 03:26 PM

The computer is connected directly to the cable modem. I am not running a wireless network, or any other kind of network within my home. Thank you for helping me answer this question of why the local host name is changing suddenly. That has never happened before.
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#4 User is offline   smart72in 

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Posted 27 June 2008 - 09:58 PM

The same happened to me yesterday. Did you get to any conclusion as to why it has happened? Thank you.
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#5 User is offline   marmac 

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Posted 20 March 2009 - 08:09 AM

This just happened to me this morning (I'm running 10.5.6); never happened before; now I'm curious... I'm running this on a mongrel home network with lots of other boxes running various OS (Tiger, Win XP, Win Vista, Ubuntu), some wireless, some wired; there's also a network printer in the mix. I'm the admin, nobody else has rights to the router, there's no file sharing turned on with my box.



I know it's not the most secure situation, but I'm just wondering what the message means ... basically, should I be worried?
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#6 User is offline   smax013 

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Posted 20 March 2009 - 01:42 PM

marmac said:


This just happened to me this morning (I'm running 10.5.6); never happened before; now I'm curious... I'm running this on a mongrel home network with lots of other boxes running various OS (Tiger, Win XP, Win Vista, Ubuntu), some wireless, some wired; there's also a network printer in the mix. I'm the admin, nobody else has rights to the router, there's no file sharing turned on with my box.





I know it's not the most secure situation, but I'm just wondering what the message means ... basically, should I be worried?




The older case (i.e. the original post) made sense to me. If the Mac was connected to cable modem directly, then it was DIRECTLY on the local area network of the cable company. Thus, ANY other Mac on the same node (typically in the same neighborhood or immediate local area) with the same local host name should produce this error.

In your case, however, if you are "behind" a router, then you are on a private network and it will only matter what computers are on your local private network...NOT what is on the local area network node of the cable system. So, unless YOU have another computer with the same local host name, in theory such a message should not happen. The only possibilities that I can think of off the top of my head is that someone using one of your other Mac's changed the local host name and creating a conflict OR someone accessed your wireless network (what security are you running on the wireless network?) with a Mac with the same local host name....OR it is just some error/bug.
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#7 User is offline   jmyii 

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Posted 14 August 2009 - 02:53 PM

I'm going for the "just some bug/error thing" since this just happend to me too. I'm a very new mac user, but my hostname is

myfirstname-mylastnames-imac

as in

john-smiths-imac

Chances of another one of those showing up seem fairly slim, but when I got back to my mac at the end of the day, it was

john-smiths-imac-2

Love to hear any advice from the experienced Mac types out there
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#8 User is offline   Kismet 

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Posted 13 July 2010 - 08:18 PM

This happens to me also ... single user direct to cable. I think it is the cable provider when the connection is dropped. The computer still thinks the old IP is active and when it sees a new IP, it sets up a new local hostname. So it is not an Apple OS problem per se, but a drop in service by the provider.
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#9 User is offline   PeterA.Kemmer 

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Posted 09 November 2010 - 11:12 AM

I've had the same or a similar issue. My computer was constantly renaming itself with a (2) every time it booted, after a system lockup. I tracked the issue down to CD/DVD sharing... when turned off the problem went away.

When CD/DVD sharing was on, I could not change the name back to the original version, it would get rejected and immediately set back to the version with "(2)", displaying the message:

The name of your computer "Name" is already in use on this network. The name has been changed to "Name (2)" automatically.

With CD/DVD sharing turned off, I could name my computer whatever I liked, even back to the original name. Turning DVD/CD sharing back on again would instantly rename my Mac. It's very persistent bug!

Fortunately I found a fix. I was able to get rid of the problem by toggling Bonjour, as described here:

http://tech.karbassi...-mdnsresponder/

To turn Bonjour off:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

To turn it back on:

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

Toggling Bonjour (mDNSResponder) forced a reset of something on my system somewhere, and now I no longer see the issue on reboot, even with CD/DVD sharing turned on. I can turn sharing on and off at will, and my computer is never renamed. Success!

I don't think this problem has to do with CD/DVD sharing specifically... I think it's a bug in Bonjour. I've seen threads where people have complained about this issue because of printer sharing, or remote management! My guess is that a crash can cause a mDNSResponder config corruption, tricking Bonjour to share devices or services using the same name as your computer, forcing the name conflict.

In any case, I hope this fix works for you too. I know I'm a lot happier now that there isn't a lingering issue on my box!
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