/docker-tips-n-tools

Docker Debugging Tips and Tools

Primary LanguageShell

Docker Debugging Tips and Tools

This repository contains tools and solutions to problems I encountered while working with docker.

Docker Tips

When using FROM scratch, it is essential to copy ld-linux and ld.so.cache, unless all executables are statically linked. Otherwise, you will get the following error message:

standard_init_linux.go:190: exec user process caused "no such file or directory"

There can be other reasons for that error message as well; for example, if there is no shell in the container but the shell form of ENTRYPOINT is used, or if the shell after hash-bang doesn't exist.

Example for how to copy 64bit ld-linux:

FROM scratch as server

# ESSENTIAL! dynamic library loader is always needed
COPY --from=build /lib64/ld-linux-x86-64.so.2  /lib64/
COPY --from=build /etc/ld.so.cache /etc/ld.so.cache

# shell is needed for ENTRYPOINT and ENV
COPY --from=build /bin/dash /bin/sh

build can be a previous stage, or a distribution such as ubuntu:18.04.

Tools

  • The tools directory contains statically linked shells (bash, sash), strace, and ls. Once the shell is working, the ldd script can display potentially missing libraries. Manually, you may also execute:

    /lib64/ld-linux-x86-64.so.2 --list /bin/ls

  • The cp-libs.sh script finds out which shared libraries a given executable needs and copies them into a given folder.