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I want to be able to plug my iPhone in to my main computer and have a fire-and-forget sync happen with iTunes automatically. But leaving the box(es) ticked about doing this appears to be a device option, not a computer option. Thus, when connecting to another PC (e.g. just to charge, or grab a photo), I have to wait whilst iTunes starts up and the device does some strange mini-sync (that doesn't seem to actually do anything other than lose track marks, scrobbles etc.). Have I got something set wrong?

Both the main machine used for syncing and the second machine this is most often a problem on are Windows machines. However, I have also seen it happen on a Macbook Air.

The situation which I envisage is:

  • Computer A is synced to iPhone A
  • Computer B is synced to iPhone B
  • User A wants to be able to plug in to computer A, triggering an automatic backup and sync
  • User B wants to be able to plug in to computer B, triggering an automatic backup and sync
  • However, User A wants to be able to plug in to Computer B (e.g. to charge, to look at photos) without starting iTunes starting or performing any kind of sync whatsoever.
  • Likewise for User B on Computer B (or Computer C,D...)
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iTunes/iPhone syncing is done on a "per Mac" basis. In iTunes Preferences, go to Devices, and check the box for "Prevent iPods, iPhones, and iPads from syncing automatically". This will prevent iTunes from opening when a device is plugged in.

UPDATE: There used to be in previous versions of iTunes, in the old "Syncing" Preferences, a way to disable automatic syncing and that prevented iTunes from even opening. But it seems they have changed the behavior because searching for answers on other sites yield the same behavior but in previous versions of iTunes. I set this preference ages ago, so the preference must be holding over.

In response to your comments:

iTunes still starts, still does some kind of mini-sync, but doesn't recognise the name of the phone or allow access to its contents.

Are you sure you are syncing with the iTunes install you originally started with? Syncing is strictly a one-to-one relationship for iPhones and iTunes. Once you sync an iPhone to an iTunes install and wish to sync with a different one (like on another Mac), you are then forced to clear the phone and start anew.

My iTunes behaves the way you are describing, but when I plug in my iPhone, I get the "mini-sync" you mention because that's the device registering with the OS and iTunes that it exists and iTunes puling needed info to interact with it. Can't really get around that one.

it would prevent the machine being used at all for syncing, no?

No. You could still sync if you wanted, but that's if you are syncing with the iTunes install that recognizes the phone. Otherwise, see my comment above.

BTW, save the downvoting for the really egregious answers. Downvoting costs points. Otherwise, just leave it alone.

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I cannot downvote, however: the result of doing this is that iTunes still starts, still does some kind of mini-sync, but doesn't recognise the name of the phone or allow access to its contents. On ejecting and disconnecting, the music library needs to rebuild itself on the phone. I confirmed I had used the setting, quit iTunes and tried again, with exactly the same result (albeit, could access contents this time). – Sam Brightman Sep 18 '10 at 11:15
Furthermore, even if this worked, it would prevent the machine being used at all for syncing, no? If you want to have iPhone A synced with computer A and iPhone B with computer B, you would not be able to use A with B for charging/playing music/grabbing photos etc. – Sam Brightman Sep 18 '10 at 11:17
To be clear: the preference you describe still exists, but it doesn't prevent iTunes from opening. Also, I know the difference between the two PCs. The PC that the phone is NOT synced to also opens iTunes/mini-syncs, even with the preference checked. With the preference checked, it seemed to cause actual damage to the phone (corrupt name, library) which had not occurred before. – Sam Brightman Sep 20 '10 at 5:48
I still don't see how this would work with a second phone I wanted to sync with the second PC - if the preference worked as described, iTunes would not open...? Hence no sync? I'm aware of how downvoting works. – Sam Brightman Sep 20 '10 at 5:50
Then the behavior of iTunes must have changed. All I ever did was disable automatic syncing in iTunes under the old Syncing preference pane and that prevented iTunes from ever opening automatically; there was never any other place to set this behavior, as far as I remember. At the same time, I've never once had problems with syncing any device except when syncing to a new machine, and even then, I got a warning window that allowed me to cancel before syncing. – Philip Regan Sep 20 '10 at 10:05

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