Here's what worked for me (from imobiledevice.org):
When your device is plugged in, close out the error. Then run
idevicepair unpair && idevicepair pair
Then unplug your device and plug it back in.
Also, if it worked in the first place, but then you reset the iPhone (used Erase all Content and Settings option in the Reset menu in Settings) and it stopped mounting, then the solution is to remove the ~/.config/libimobiledevice/ directory and then replug your iPhone.
Plug in the iPhone while the computer is either suspended or shut down, or while the Grub startup screen is displayed.
If you get the popup prompt on the iPhone, tell it to trust the computer, or allow access (however it is worded). If it works for you like it does for me, when the computer starts up the iPhone will be mounted and you will have access lots of data, much more that the folks at Apple would want you to see. Be careful in there.
Edit: I am using an iPhone 6s and Ubuntu 14.04 LTS. This version of Ubuntu ships with libimobiledevice, which handles the mounting of the iPhone, as I understand it.
Here's what worked for me (from imobiledevice.org):
When your device is plugged in, close out the error. Then run
Then unplug your device and plug it back in.
Also, if it worked in the first place, but then you reset the iPhone (used Erase all Content and Settings option in the Reset menu in Settings) and it stopped mounting, then the solution is to remove the
~/.config/libimobiledevice/
directory and then replug your iPhone.The only thing that worked for me:
Plug in the iPhone while the computer is either suspended or shut down, or while the Grub startup screen is displayed.
If you get the popup prompt on the iPhone, tell it to trust the computer, or allow access (however it is worded). If it works for you like it does for me, when the computer starts up the iPhone will be mounted and you will have access lots of data, much more that the folks at Apple would want you to see. Be careful in there.
Edit: I am using an iPhone 6s and Ubuntu 14.04 LTS. This version of Ubuntu ships with libimobiledevice, which handles the mounting of the iPhone, as I understand it.