I also came across a similar issue when using VS Code with remote containers and Docker Desktop (WSL2).

I debugged the problem by adding in a --pre-get-sources-script=ls -l "repo_directory", i.e. in the OP's case:

# docker run --name=runner --privileged -t --rm \
 -v /var/run/docker.sock:/var/run/docker.sock  \
 -v /tmp/.gitlab-runner/:/etc/gitlab-runner \
 -v {PWD} \
 --workdir $PWD \
 --pre-get-sources-script=ls -l /home/fox/Work/docker/core-application/../.git/modules/core-application \
 gitlab/gitlab-runner exec docker \
  --builds-dir /tmp/builds/ Rspec

In my case, the directory listing (ls -l ...) came up empty! I'm assuming that it mounts the directory as a volume within the container as the same name (/fubar:/fubar), which in my case isn't going to work as it is Docker Desktop with vscode remote containers.

My fix was was to add my named volume as a parameter to a secondary directory, and then setting the --clone-url to point to that directory.

Something like:

# pwd
/workspace/fubar
# gitlab-runner --debug exec docker \
  --docker-volumes vscode-workspace:/workspace2 \
  --clone-url=file:///workspace2/fubar \
  validate;
[output truncated]
...
Starting container 3d49d8e8b977177f34beeae3ae5f09eba288332e109ad79f133e0f160377908b ...  job=1 project=0
Fetching changes...
Initialized empty Git repository in /builds/project-0/.git/
Created fresh repository.
Checking out d1a39a4d as detached HEAD (ref is feature/FU-123)...

Skipping Git submodules setup
Executing build stage                               build_stage=restore_cache job=1 project=0
Skipping stage (nothing to do)                      build_stage=restore_cache job=1 project=0
Executing build stage                               build_stage=download_artifacts job=1 project=0
Skipping stage (nothing to do)                      build_stage=download_artifacts job=1 project=0
Executing build stage                               build_stage=step_script job=1 project=0
Executing "step_script" stage of the job script
...

I had originally tried changing the --pre-get-sources-script to be cp -R /workspace2/fubar /workspace/ but that complained that the target directory was read-only. Using the --clone-url=file:///workspace2/fubar worked, so I've left it that way.

Deprecated since 2024-05 (see edit)

Only for gitlab-runner < 17.0.

• See gitlab issue.
• See gitlab docu

I use this docker-based approach:

Edit: 2024-05

docker run --entrypoint bash --rm -w "PWD:$PWD" -v /var/run/docker.sock:/var/run/docker.sock gitlab/gitlab-runner:v15.11.1 -c 'git config --global --add safe.directory "*";gitlab-runner exec docker test'

Thanks to user Ivo Smits who reported a successful test with gitlab-runner:v15.11.1

Edit: 2022-10

For all git versions > 2.35.2. You must add safe.directory within the container to avoid fatal: detected dubious ownership in repository at.... This also true for patched git versions < 2.35.2. The old command will not work anymore.

Details

0. Create a git repo to test this answer

mkdir my-git-project
cd my-git-project
git init
git commit --allow-empty -m"Initialize repo to showcase gitlab-runner locally."

1. Go to your git directory

cd my-git-project

2. Create a .gitlab-ci.yml

Example .gitlab-ci.yml

image: alpine

test:
  script:
    - echo "Hello Gitlab-Runner"

3. Create a docker container with your project dir mounted

docker run -d \
  --name gitlab-runner \
  --restart always \
  -v "PWD" \
  -v /var/run/docker.sock:/var/run/docker.sock \
  gitlab/gitlab-runner:latest

(-d) run container in background and print container ID

(--restart always) or not?

(-v "PWD") Mount current directory into the current directory of the container - Note: On Windows you could bind your dir to a fixed location, e.g. -v "${PWD}:/opt/myapp". Also $PWD will only work at powershell not at cmd

(-v /var/run/docker.sock:/var/run/docker.sock) This gives the container access to the docker socket of the host so it can start "sibling containers" (e.g. Alpine).

(gitlab/gitlab-runner:latest) Just the latest available image from dockerhub.

4. Execute with

Avoid fatal: detected dubious ownership in repository at... More info

docker exec -it -w $PWD gitlab-runner git config --global --add safe.directory "*"

Actual execution

docker exec -it -w $PWD gitlab-runner gitlab-runner exec docker test
#                ^          ^           ^            ^     ^      ^
#                |          |           |            |     |      |
#               (a)        (b)         (c)          (d)   (e)    (f)

(a) Working dir within the container. Note: On Windows you could use a fixed location, e.g. /opt/myapp.

(b) Name of the docker container

(c) Execute the command "gitlab-runner" within the docker container

(d)(e)(f) run gitlab-runner with "docker executer" and run a job named "test"

5. Prints

...
Executing "step_script" stage of the job script
$ echo "Hello Gitlab-Runner"
Hello Gitlab-Runner
Job succeeded
...

Note: The runner will only work on the commited state of your code base. Uncommited changes will be ignored. Exception: The .gitlab-ci.yml itself does not have be commited to be taken into account.

Note: There are some limitations running locally. Have a look at limitations of gitlab runner locally.

since gitlab 17, the feature is removed https://docs.gitlab.com/runner/commands/#gitlab-runner-exec-removed