Docker: Cannot execute binary file

Question

I can't run any binary in my docker container.

Dockerfile:

FROM ubuntu:eoan AS compiler-build

RUN apt-get update && \
    dpkg --add-architecture i386 && \
    apt-get install -y gcc \
                       gcc-multilib \
                       make \
                       cmake \
                       git \
                       python3.8 \
                       bash

WORKDIR /home
ADD . /home/pawn
RUN mkdir build
WORKDIR /home/build
ENTRYPOINT ["/bin/bash"]
CMD ["/bin/bash"]

I can't even use file builtin:

[root@LAPTOP-EJ5BH6DJ compiler]:~/dev/private/SAMP/compiler (v13.11.0) (master) dc run compiler file bash
/usr/bin/file: /usr/bin/file: cannot execute binary file

Answer 1

From this forum thread:

This error occurs when you use a shell in your entrypoint without the "-c" argument

So, if you change your Dockerfile to end with

ENTRYPOINT [ "/bin/bash", "-l", "-c" ]

then you can run binary files.

Note the purpose of the options for /bin/bash, from the manpage:

• -l: Make bash act as if it had been invoked as a login shell

• -c: If the -c option is present, then commands are read from the first non-option argument command_string. If there are arguments after the command_string, the first argument is assigned to $0 and any remaining arguments are assigned to the positional parameters. The assignment to $0 sets the name of the shell, which is used in warning and error messages.

Additionally, this article is a worthwhile read on how to use both ENTRYPOINT and CMD together, and what their differences are.

EDIT: Here's another article that goes into a trivial (but clearer than the first article) example using the echo shell builtin.

EDIT: Here's an adaptation of the trivial example from the second article I linked:

FROM ubuntu
ENTRYPOINT [ "/bin/bash", "-l", "-c" ]
CMD [ "ls" ]

$ docker build -t test .

$ docker run --rm test
bin
boot
...
var

$ docker run --rm test "ls etc"
adduser.conf
alternatives
apt
...
update-motd.d
xattr.conf

Note the " around ls /etc. Without the quotes, the argument /etc doesn't seem to be passed to the ls command as I might expect.