I’m trying to use an image from Docker Hub, makarius/isabelle , for automated builds. However, if usage of this image is enabled, checking out my repository with actions/checkout@v2 fails with the error EACCES: permission denied, open '/__w/⟨repository-name⟩/⟨repository-name⟩/⟨uuid⟩.tar.gz'. The repository is downloaded using the GitHub REST API.

A minimal workflow that triggers this error is as follows:

name: Automated checkout
on: [push]
jobs:

checkout:

runs-on: ubuntu-latest

container: makarius/isabelle

steps:

- name: Check out repository

uses: actions/checkout@v2

Unfortunately, the above error message, while mentioning a path, does not tell, on which machine the respective directories should exist and what permissions they should have.

From its documentation, I cannot tell, what actions/checkout@v2 is trying to do precisely. Should the virtual host write the data into the container but doesn’t have write permissions? Or should the container try to copy the data from the virtual host onto its own disk but can’t either read or write the data?

Are there any constraints a docker image to be used with actions/checkout@v2 has to fulfill? If yes, where are these documented?

The particular image I’m trying to employ uses a non-privileged user for its entry point. Could this be the problem?