TIL: how to disable cron for GitHub forks

GitHub Actions has a useful feature to trigger workflows on a cron schedule. For example:

name: Test

on:
  push:
  pull_request:
  schedule:
    - cron: "0 6 * * *" # daily at 6am

jobs:
  test:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v3

But if a contributor has enabled GitHub Actions on their fork (which I recommend: test your contributions before opening a PR), it also runs the cron on their fork. This not only uses up extra CI resources on the fork:

It also sends a regular email to the contributor when the workflow fails:

Instead, we only need to run the cron for the upstream. For example, for a https://github.com/octocat/hello-world repo, add:

 jobs:
   test:
+    if: ${{ github.repository_owner == 'octocat' || github.event_name != 'schedule' }}
     runs-on: ubuntu-latest

This only runs the schedule trigger for the octocat upstream, and all other triggers run for both upstream and forks.

Also #

For simpler workflows that only trigger on a cron, such as stalebot or CodeQL runs, we can add a simpler condition.

For example:

name: Close stale issues

on:
  schedule:
    - cron: "10 0 * * *" # daily at 12:10am

jobs:
  stale:
    runs-on: ubuntu-latest

    steps:
      - name: "Check issues"
        uses: actions/stale@v8

We can completely disable it for forks:

 jobs:
   stale:
+    if: github.repository_owner == 'octocat'
     runs-on: ubuntu-latest

PS #

Use single quotes in these lines, double quotes are invalid here (Unexpected symbol).

Thanks #

To Alex Waygood for the tip.

To the British Library and Flickr Commons for the illustration of a chronograph.