macOS-15 runner fails to connect to the iOS simulator

[smoogipoo]

Description

Hi, I'm coming from a recently closed issue report: #12758

The suggested solution listed is to xcode-select and (potentially?) download the iOS platform. For us, we're using Xcode 16.4 and downloading the latest platform (no args).

50% of the time, this works and resolves the original issue. 50% of the time, it results in another issue:

Unable to connect to simulator.

See for example this run: https://github.com/ppy/osu/actions/runs/17115759241/job/48546246056?pr=33649

Please help!

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 22.04
• Ubuntu 24.04
• macOS 13
• macOS 13 Arm64
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• Windows Server 2019
• Windows Server 2022
• Windows Server 2025

Image version and build link

20250818.2206

Is it regression?

Yes, 20250722.2025, https://github.com/ppy/osu/actions/runs/17068261106/job/48390499090

Expected behavior

The "Use Xcode 16.4" step in the linked workflow to work.

Actual behavior

Unable to connect to simulator.

Repro steps

sudo xcode-select -switch /Applications/Xcode_16.4.app
xcodebuild -downloadPlatform iOS

[smoogipoo]

Have also tracked down a pass and fail in a more recent runner image 20250811.2170, so seems intermittent on the same image.

[Jon889]

I've also found this, even before the recent changes, that sometimes an agent will give the error Unable to connect to simulator. when running xcodebuild -downloadPlatform. @erik-bershel It seems there is an inconsistency in the runners, even within the same image version. Perhaps you could add the workaround below and information about the error to the comment in the locked thread.

@smoogipoo
As a workaround I run a simctl command before and that seems to fix it, and only adds a couple of seconds to the run time.
This is script I use to set up each job, the second line is the workaround, and the versions for Xcode and simulator could be anything.

sudo xcode-select -s "/Applications/Xcode_16.4.app"
xcrun simctl list > /dev/null # Required to prevent the next command from sometimes not working
xcodebuild -downloadPlatform iOS -buildVersion 17.4

(I know there is a community Task that does installation but as a company policy we're not allowed to use 3rd party tasks)

[erik-bershel]

Hey there! 👋

This is actually a completely different issue for a number of reasons. The original issue was missing simulators for some Xcodes. For Xcode 16.4, this shouldn't be a problem at all - we install all the major simulators for it beforehand. So yes, you've brought a new interesting case that will be useful to investigate and fix. 🤔
The repro steps are simple, there's enough information, so it shouldn't be hard to reproduce the issue - we'll come back after further investigation. It seems the reason is on our side - we need to conduct a couple of checks.

[erik-bershel]

@smoogipoo

An easier workaround for those using Xcode 16.4 would be to not use the xcodebuilds -downloadPlatform iOS command. This is not required for this version of Xcode - all simulators for it are already installed.

Example builds: 1, 2.

[alainib]

same error for me after the failure and fix from #12758 (comment)

i runned the CI on github 3times to pass this steps. i guess i have to update to XCODE 16.4 soon

  - name: Select Xcode 16.2
    run: sudo xcode-select -switch /Applications/Xcode_16.2.app/Contents/Developer

  - name: Print Xcode version
    run: xcodebuild -version

  - name: Download iOS Platform
    run: xcodebuild -downloadPlatform iOS