Is there anyway to know what nsurlsession is downloading? My iCloud Drive is only 30GB. Most of the Apple Music and Photos are already on my Mac. I don't even generate 1GB of Photos or video per month.

And yet nsurlsessiond is downloading 100s of GB of data. This is 10 times more then all the App update, OSX Update and iCloud Data combined !!!

Is this a bug or have i been hacked? I send a support letter to Apple and no response.

  • You can get some information from Activity Monitor. Open Activity Monitor and select nsurlsessiond. Then double click it and select Open Files and Ports. This may not provide all the information you're looking for however it's where I'd start. Here are a few command line utilities you can use in a Terminal: fs_usage, iosnoop, opensnoop and dtrace. iosnoop and opensnoop make use of dtrace. You can read the manages on these commands by, man $command e.g.: man fs_usage Nov 30, 2015 at 14:43
  • I have a hypothesis that chromecast of a youtube video may be causing this in my case...
    – drevicko
    Nov 24, 2017 at 9:00
  • @drevicko This question was a long time ago and i figured it out. It was iCloud. Specifically Whatsapp. If you have Whatsapp and uses the Whatsapp's internal iCloud Backup. You should disable it.
    – Ksec
    Dec 1, 2017 at 12:49

1 Answer 1


Whatsapp was causing it. Whatsapp's internal backup system to iCloud Drive. If you have have your Mac setup to sync with iCloud, it will prefetch all iCloud drive content to your Mac as cache, which includes your Whatsapp Backup. Since your whatsapp backup are constantly renewed, the Mac will constantly have to fetch the newer version.

For me the Whatsapp backup was 5GB, which is why it easily consume all your bandwith. This problem could also be the same for any other Apps that backup to iCloud. Disable the Whatsapp Internal iCloud Drive backup was the solution, as whatsapp itself is backed up when you do full iPhone Backup to iCloud.

Problem has been reported to both Apple and Whatsapp few weeks after this post, in 2016 i tested it and the problem was still there. Not sure about it now.

  • I would have expected Apple to diff the Whatsapp backup on iCloud with the local cache, and download only the bytes that changed. Strange it doesn't do this. Dec 1, 2017 at 20:25
  • Apple doesn't diff Apps in Apps store years after Google have done it. So I am not surprised they dont do it. ( yet ) Even if they do diff it, it is silly to have it cached anyway.
    – Ksec
    Feb 13, 2018 at 7:48

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