How to identify why a program is not starting inside docker

Question

I have a docker image which has a c++ executable with dependencies packed into it. This executable runs fine outside docker environment and i have tested it multiple times. However inside docker it stops immediately as and when started.

To debug i have added a std::cout << "Main 1" << std::endl as soon as main() function is called. But even this is not being printed when i start the executable inside docker.

Any tips on how to debug this issue.

Adding docker file which is used to build the docker image.

FROM ubuntu:18.04

# install app dependencies
RUN apt-get -yqq update \
        && apt-get -yqq dist-upgrade \
        && apt-get -yqq install apt-utils libgomp1 libprotobuf10 libboost-thread1.65.1 libboost-filesystem1.65.1 libopencv-core3.2 libopencv-imgproc3.2 libopencv-imgcodecs3.2 libjpeg-turbo8 libpo
        && apt-get -yqq remove systemd cups perl ffmpeg apt-utils \
        && rm -rf /var/lib/apt/lists/*

# create app folder
RUN mkdir -p /opt/aimes

# copy app, dependencies and config
COPY deps/aimes /opt/aimes/
COPY deps/*.* /opt/aimes/
COPY deps/config /opt/aimes/config

# copy wrapper script
COPY run-es.sh /opt/aimes/

# run command
WORKDIR /opt/aimes
ENV LD_LIBRARY_PATH .
ENTRYPOINT ["./run-es.sh"]

I could run commands like cat or ls -al inside docker. I could see all files. Even ldd on the executable is returning all linked libraries and i dont see any `not found` in that list. — Sudheendra S.N, Jun 13 '20 at 05:38
I have updated the question with Dockerfile that is used for preparing docker image. — Sudheendra S.N, Jun 13 '20 at 05:43
See https://stackoverflow.com/questions/42029834/gdb-in-docker-container-returns-ptrace-operation-not-permitted for how to use gdb — Alan Birtles, Jun 13 '20 at 06:34
If you've solved your problem you can answer your own question to help others in the future — Alan Birtles, Jun 13 '20 at 08:43

score 0 · Answer 1 · answered Jun 13 '20 at 16:19

Adding --cap-add=SYS_PTRACE to docker run command helped in finding out issue using gdb.

Also the solution was to add the above option to docker run command, since the exe required root permissions.

Below command solved my issue.

docker run --cap-add=SYS_PTRACE -it --rm

How to identify why a program is not starting inside docker

1 Answers1