Failed to find a DDI

Can you provide the output of devicectl list preferredDDI?

— Ed Ford,  DTS Engineer

Hi Ed, thanks for the quick reply. I tried to reply directly in the forum with the requested output, but I keep receiving an error message ("Your post couldn’t be saved. Please try again in a few minutes."). It seems I cannot currently post a follow-up reply. The output: zsh: command not found: devicectl

I got this reply. 😀

I underspecified the exact command there, which is my mistake. The full command is xcrun devicectl list preferredDDI. What's that output?

— Ed Ford,  DTS Engineer

Hello, Ed,

Sorry to jump in here too… ;-)

I have the same problem after upgrading to Xcode Version 26.0 (17A324).

Thanks for mentioning the full command, until now, I had never used the command line for Xcode.

The output states that several DeveloperDiskImages are too old:

file:///Library/Developer/DeveloperDiskImages/iOS_DDI/ file:///Library/Developer/DeveloperDiskImages/tvOS_DDI/ file:///Library/Developer/DeveloperDiskImages/watchOS_DDI/ file:///Library/Developer/DeveloperDiskImages/xrOS_DDI/

"incompatibleContentReason: The DDI's CoreDevice content is too old."

Is it safe to delete them — and hope/pray that they would get properly replaced automatically?

Thanks ;-)

PS: Actually, this is exactly what I will do — and see what will happen…

Hello @haptic! As @Daniel1codes mentioned in his reply to your last message, the best and easiest solution, is to carry out a full delete of Xcode, followed by a re-install from the App Store.

I ran into this issue when I updated to Xcode 26, so I carried out a full delete of Xcode and reinstalled from App Store. This fixed the DDI issue.

Terminal commands used to fully delete Xcode:

sudo rm -rf /Applications/Xcode.app
rm -rf ~/Library/Developer/Xcode  
rm -rf ~/Library/Caches/com.apple.dt.Xcode
rm -rf ~/Library/Developer/CoreSimulator  
rm -rf ~/Library/MobileDevice   

sudo rm -rf /Library/Developer/CommandLineTools

sudo rm -rf /Library/Developer
sudo rm -rf /System/Volumes/Data/Library/Developer

rm -rf ~/Library/Preferences/com.apple.dt.Xcode.plist
rm -rf ~/Library/Application\ Support/Xcode

NOTE: If you are getting 'Operation Not Permitted' when running sudo rm -rf /Library/Developer or sudo rm -rf /System/Volumes/Data/Library/Developer manually delete them in Finder.

No. Please do not delete all of Xcode and redownload it and resintall it. That's serious overkill for what is probably a very simple problem.

Per the OP, the issue was that the system resources installer got interrupted and left the system if a partially updated state... so just finish that process.

I suggest you run:

xcrun devicectl manage ddis update

That will probably address the issue. If not, the following will reinstallt he the system resources package (including the DDIs):

sudo installer -target / -pkg $(xcode-select -p)/../Resources/Packages/XcodeSystemResources_Full.pkg

When a partial install occurs it can cause mismatched bundles across Xcode and /Library/Developer. I tried all of the following, after researching the issue for some time, xcrun devicectl manage ddis update, reinstalling XcodeSystemResources_Full.pkg, xcode-select, CLTs, clearing caches/DerivedData, deleting DDIs, resetting simulators. None worked, still got "Failed to find a DDI". Only a full removal of Xcode and reinstall fixed it.

Running the 2 commands mentioned above may resolve the issue in some cases. However, from what I've seen online after replying to several threads, many people ultimately need a full reinstall. This seems especially common when Xcode was already installed and then updated to Xcode 26 via the App Store.

Many thanks to all of you for the help! @haptic, @jsequoia, @pax26 I was finally able to solve it. I’m incredibly grateful, since it was extremely important and I was running out of time. The final solution was to completely delete Xcode via Terminal and then re-download it. The package remains intact, and now everything runs perfectly. It also works on the devices now. I only had to replace import SwiftCoreUI with import SwiftUI, otherwise everything runs really smoothly.