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10.5: Back to My Mac fails to start due to incorrect time Network
For some time now, Back to My Mac (BTMM) has failed to start on my Mac Mini at home, although it worked fine on my MacBook Pro from the same network. After trying many many different things and following a number of hints, I remembered reading that BTMM uses IPsec. IPsec tunnels require endpoints to have their clocks synced, or at least to be set to times that are relatively close to one another.

I noticed the time on my Mac Mini differed from that of my MacBook Pro by about 10 minutes, and was failing to update its local time via time.apple.com (on the Date & Time tab of the Date & Time System Preferences panel). I switched it to time.asia.apple.com, the clock updated, and BTMM connected immediately after I clicked Start in the Mobile Me System Preferences panel.

See the comments for some recommendations on which time servers to use...
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10.5: Back to My Mac fails to start due to incorrect time | 12 comments | Create New Account
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10.5: Back to My Mac fails to start due to incorrect time
Authored by: Clint MacDonald on Apr 27, '09 08:34:37AM
I remembered reading that BTMM uses IPsec. IPsec tunnels require endpoints to have their clocks synced…
Wow — obscure, really geeky, and an important troubleshooting tip for just those reasons. Thanks!

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10.5: Back to My Mac fails to start due to incorrect time
Authored by: holo on Apr 27, '09 08:37:04AM

I've had time.apple.com fail alot for me recently. I started using the asia time server instead when I noticed problems. Honestly I'm kind of glad to see that the problems weren't just me.



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: goatbar on Apr 27, '09 08:43:24AM

In order for NTP to work, it needs multiple time servers. Apple's initial ntp.conf file is not good. I recommend using the ntp pool. e.g. for folks in the United States:

cat /etc/ntp.conf
server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org
server 0.north-america.pool.ntp.org
server 1.north-america.pool.ntp.org
server 2.north-america.pool.ntp.org
server 127.127.1.0

You can then query how well ntp is doing like this:

ntpq -p -n
remote refid st t when poll reach delay offset jitter
==============================================================================
+216.184.20.83 66.220.9.122 2 u 34 128 377 153.490 68.502 241.051
x209.67.219.106 74.53.198.146 3 u 28 128 377 82.082 522.860 450.415
-174.133.44.162 132.163.4.103 2 u 31 128 377 77.303 498.074 433.132
+216.45.57.39 204.123.2.5 2 u 48 128 377 198.298 26.814 240.223
x74.208.145.168 128.59.59.177 3 u 52 128 377 76.065 511.502 421.497
*128.10.252.7 .GPS. 1 u 82 128 377 79.171 62.040 170.801
127.127.1.0 .LOCL. 5 l 6 64 377 0.000 0.000 0.001



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: mnewman on Apr 27, '09 04:21:59PM

goatbar, can you explain the "server 127.127.1.0" entry in your ntp.conf file?

---
http://www.mgnewman.com



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: j-beda on Apr 29, '09 06:47:39AM

Maybe that is his router's address? I think that many routers might have an NTP server running.



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: goatbar on May 08, '09 01:34:05PM

That would be so that if the network goes down, ntp will default back to using the computers internal clock.

-kurt



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ntp pool info
Authored by: j-beda on Apr 29, '09 06:45:11AM
Great info, I had been just using ca.pool.ntp.org in the "date and time" control panel, but edited the /etc/ntp.conf file to include the 0123 servers for ca as well as the NA ones as well. Some details of the NTP pools are at:

http://www.pool.ntp.org/

They seem to be suggesting using at least three, selecting from the closest (in networking terms) pool to you.

When I updated my ntp.conf file, and tried "ntpq -p -n", I got no change from before the edit, so I used the "Date and Time" panel in "System Preferences" to uncheck the "use network time server" box, and then checked the box again - that seems to have restarted the NTP process and loaded the new ntp.conf file. There is probably a way of doing that from the command line of course, but the checkbox was easier to find.



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: ehahn on Apr 27, '09 10:20:24AM
One shouldn't use time-a.nist.gov as the timeserver for their end user machine (desktop or laptop). This is a stratum 1 server, which should only be queried by stratum 2 servers (which act as "local" references).

One should either sync to a stratum 2 server, or sync via the pool system as described in an earlier comment.

See:
http://support.ntp.org/bin/view/Servers/RulesOfEngagement

ed

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10.5: Back to My Mac fails to start due to incorrect time
Authored by: NoLongerAnon on Apr 27, '09 10:41:19AM

@ehahn, good point. I remember I tried a Stratum 1 server at some point long ago because I couldn't seem to get anything to work. It was meant to be temporary but naturally I forgot to change it and eventually forgot that I shouldn't be using it at all. Perhaps robg will be kind enough to strike out my last line. It wasn't the main point anyway.



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: robg on May 05, '09 08:19:25AM

Done :).

-rob.



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: robg on May 05, '09 08:21:06AM

And oh yea, I credited the hint to your newly-registered name, too :)

-rob.



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10.5: Back to My Mac fails to start due to incorrect time
Authored by: kranki on Nov 25, '09 07:30:45AM
I found that unchecking/rechecking the update time automatically didn't seem to always work for me. Also, killing the ntpd task didn't seem effective either. But through googling, I found that sudo SystemStarter -d restart "Network Time" in terminal seems to reset the time immediately. (I needed this because my battery in this computer has quit and I haven't replaced it yet.) HTH

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