Reset ‘Trust This Computer’ Alert on iOS

Have you ever accidentally hit the ‘Trust this computer’ pop-up message alert on your iPhone or iPad and can’t undo it? Fear not, there is a way to solve the problem.

Most of the time the Apple ecosystem is brilliant, making your devices work seamlessly without you having to worry about them. Of course, the downside of this is when something doesn’t function as you expect it, the result is even more frustrating.

While it is annoying though, the flip-side is to have an non-closed system that you can tinker with, but is susceptible to attack and security threats. Naturally this isn’t something most of us want, and the result is that all of our possible individual needs have to be covered by Apple’s settings and options, something that just isn’t feasible.

In the case of trusting a computer though – ie. allowing an individual computer access to your iOS device – there are only two options: Hit ‘Trust’ and the computer is permanently trusted; or hit ‘Don’t Trust’ and the message continues to pop-up every time you connect your device to it.

While this sounds reasonable, there are a huge percentage of users who regularly plug their iPhones and iPads into Macs and PCs to charge, but don’t want the computer to have access to any of the device’s content. If, for example, you trust your work Mac, anyone can open Photos and view all your images with your iPhone connected. Frustratingly the only way around this is to dismiss the pop-up alert every single time.

A more sensible approach would be to have more options in the pop-up message (“Trust This Computer? Your settings and data will be accessible from this computer when connected”), such as ‘Trust once’ or ‘Never Trust’. Similarly there could be a section in the Settings of the iOS device with a list trusted computers that you can view and delete if necessary. For whatever reason, though, this isn’t in Apple’s thinking.

So if like me, once in a hundred times of hitting ‘Don’t Trust’ you actually hit ‘Trust’ by mistake, here’s how to undo it and untrust the computer again:

How to Untrust / Remove ‘Trust this computer’ from your Mac/PC

1. On the Mac* you have trusted click ‘Go’ in the top menu bar in Finder and select ‘Go to folder…’. Alternatively use the keyboard shortcut Shift+Cmd+G with any Finder window selected.

2. In the pop-up field enter the address ‘/var/db/lockdown’. This will open the lockdown folder which contains a series of .plist files, each of which corresponds to a device you have trusted.

3. Delete the most recent .plist file, whose date modified corresponds with the date that you accidentally trusted the computer. (If you have the folder view set to icons, you’ll need to change it to list view in order to see each file’s modified date.) Then empty the Trash. You may also need to restart both the Mac and your iOS device.

4. That’s it. Disconnect your iOS device if it wasn’t already and reconnect it and you should get the usual ‘Trust/Don’t Trust’ pop-up again.

*Have a PC with Windows? Instructions for finding the lockdown folder on Windows are listed on Apple’s Support pages.

There are more complex instructions over on StackExchange that have foolproof methods for determining the correct .plist file using MAC addresses, but if you only have a couple of devices and know when you accidentally hit ‘Trust’ there’s no chance of you deleting the wrong file, and even if you did it wouldn’t cause any more harm than having to retrust other devices.