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macOS hostname DNS resolution failure #12562

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@externl

Description

@externl

Description

Getting the hostname of the runner then pinging it fails.

Maybe related to #12560, but we started experiencing these issues at different times. This issue is intermittent.

Run set -x
++ hostname
+ echo 'Hostname: Mac-1752083390647.local'
Hostname: Mac-1752083390647.local
++ hostname -f
+ echo 'Fully Qualified Domain Name: Mac-1752083390647.local'
Fully Qualified Domain Name: Mac-1752083390647.local
+ echo 'Pinging localhost...'
Pinging localhost...
+ ping -c 1 localhost
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.157 ms
--- localhost ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.157/0.157/0.157/0.000 ms
+ echo 'Pinging hostname...'
Pinging hostname...
++ hostname
+ ping -c 1 Mac-1752083390647.local
ping: cannot resolve Mac-1752083390647.local: Unknown host

See also my test workflow failure: https://github.com/externl/sandbox/actions/runs/16176523130/job/45662855741

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

Runner Image
  Image: macos-15-arm64
  Version: 20250630.1914
  Included Software: https://github.com/actions/runner-images/blob/macos-15-arm64/20250630.1914/images/macos/macos-15-arm64-Readme.md
  Image Release: https://github.com/actions/runner-images/releases/tag/macos-15-arm64%2F20250630.1914

Is it regression?

Yes

Expected behavior

Hostname should be resolvable.

Actual behavior

Hostname is not always resolvable. If it works once on a runner it seems to always work, but if it fails it will always fail.

ping: cannot resolve Mac-1752083390647.local: Unknown host
```
where `Mac-1752083390647.local` is hostname

### Repro steps

ping -c 1 $(hostname)

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