$ cat /gen-source/Dockerfile.gen
FROM image-registry.openshift-image-registry.svc:5000/openshift/ruby:latest
LABEL "io.openshift.s2i.build.image"="image-registry.openshift-image-registry.svc:5000/openshift/ruby:latest" \
      "io.openshift.s2i.build.source-location"="."

USER root
# Copying in source code
COPY upload/src /tmp/src
# Change file ownership to the assemble user. Builder image must support chown command.
RUN chown -R 1001:0 /tmp/src
USER 1001
# Assemble script sourced from builder image based on user input or image metadata.
# If this file does not exist in the image, the build will fail.
RUN /usr/libexec/s2i/assemble <---- this is not a custom script
# Run script sourced from builder image based on user input or image metadata.
# If this file does not exist in the image, the build will fail.
CMD /usr/libexec/s2i/run 

I0312 02:33:08.280832      17 build.go:52] Running S2I version "unknown"
I0312 02:33:08.281224      17 util.go:70] Getting docker credentials for image-registry.openshift-image-registry.svc:5000/openshift/ruby:latest
I0312 02:33:08.281432      17 util.go:81] Using serviceaccount@example.org[image-registry.openshift-image-registry.svc:5000] credentials for pulling image-registry.openshift-image-registry.svc:5000/openshift/ruby:latest
I0312 02:33:08.517391      17 build.go:170] 
Source:				.
Output Image Tag:		
Environment:			
Environment File:		/env-vars/env-file
Labels:				
Incremental Build:		disabled
Remove Old Build:		disabled
Builder Pull Policy:		if-not-present
Previous Image Pull Policy:	if-not-present
Quiet:				disabled
Layered Build:			disabled
Docker Endpoint:		unix:///var/run/docker.sock
Docker Pull Config:		/tekton/home/.docker/config.json
Docker Pull User:		serviceaccount

I0312 02:33:08.517742      17 scm.go:20] DownloadForSource .
I0312 02:33:08.518316      17 download.go:39] Copying sources from "." to "/gen-source/upload/src"
I0312 02:33:08.518360      17 ignore.go:66] .s2iignore file does not exist
I0312 02:33:08.518476      17 fs.go:247] Directory ".git" ignored
I0312 02:33:08.518523      17 fs.go:250] D ".s2i" -> "/gen-source/upload/src/.s2i"
I0312 02:33:08.518640      17 fs.go:250] D ".s2i/bin" -> "/gen-source/upload/src/.s2i/bin"
I0312 02:33:08.518791      17 fs.go:268] F ".s2i/bin/assemble" -> "/gen-source/upload/src/.s2i/bin/assemble"
I0312 02:33:08.518994      17 fs.go:268] F "Gemfile" -> "/gen-source/upload/src/Gemfile"
I0312 02:33:08.520134      17 fs.go:268] F "Gemfile.lock" -> "/gen-source/upload/src/Gemfile.lock"
I0312 02:33:08.520321      17 fs.go:268] F "README.md" -> "/gen-source/upload/src/README.md"
I0312 02:33:08.520539      17 fs.go:268] F "Rakefile" -> "/gen-source/upload/src/Rakefile"
I0312 02:33:08.520766      17 fs.go:268] F "app.rb" -> "/gen-source/upload/src/app.rb"
I0312 02:33:08.520995      17 fs.go:268] F "config.ru" -> "/gen-source/upload/src/config.ru"
I0312 02:33:08.521239      17 fs.go:268] F "index.html" -> "/gen-source/upload/src/index.html"
I0312 02:33:08.521412      17 fs.go:250] D "pipeline" -> "/gen-source/upload/src/pipeline"
I0312 02:33:08.521614      17 fs.go:268] F "pipeline/Jenkinsfile" -> "/gen-source/upload/src/pipeline/Jenkinsfile"
I0312 02:33:08.521833      17 fs.go:268] F "pipeline/pipeline.yaml" -> "/gen-source/upload/src/pipeline/pipeline.yaml"
I0312 02:33:08.522073      17 fs.go:250] D "test" -> "/gen-source/upload/src/test"
I0312 02:33:08.522262      17 fs.go:268] F "test/test-app.rb" -> "/gen-source/upload/src/test/test-app.rb"
I0312 02:33:08.522459      17 install.go:269] Using "assemble" installed from "<source-dir>/.s2i/bin/assemble"
I0312 02:33:08.522583      17 install.go:269] Using "run" installed from "image:///usr/libexec/s2i/run"
I0312 02:33:08.522694      17 install.go:269] Using "save-artifacts" installed from "image:///usr/libexec/s2i/save-artifacts"
I0312 02:33:08.522784      17 ignore.go:66] .s2iignore file does not exist
I0312 02:33:08.522832      17 dockerfile.go:115] Constructing image build context directory at /gen-source/
I0312 02:33:08.522944      17 dockerfile.go:490] No user environment provided (no environment file found in application sources)
I0312 02:33:08.522998      17 dockerfile.go:223] Processing injected inputs: api.VolumeList(nil)
I0312 02:33:08.523059      17 dockerfile.go:225] Processed injected inputs: api.VolumeList(nil)
I0312 02:33:08.523236      17 dockerfile.go:296] Wrote custom Dockerfile to /gen-source/Dockerfile.gen
I0312 02:33:08.523331      17 build.go:180] Application dockerfile generated in /gen-source/Dockerfile.gen