create minimalistic image - exec: no such file or directory

Question

I'm learning Docker and I'm trying to create the most simple and light image as possible. That's what I did.

• helloworld directory:

$ ls
Dockerfile  helloworld.c

• helloworld.c

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    return 0;
}

• Dockerfile

FROM scratch
COPY helloworld /
CMD ["/helloworld"]

I compiled the .c file:

$ gcc -o helloworld helloworld.c 
$ ./helloworld
Hello world!

Then I created the image:

$ docker build --tag helloworld .
[+] Building 0.2s (5/5) FINISHED                                                                                                                                                                                                     
 => [internal] load build definition from Dockerfile                                                                                                                                                                            0.0s
 => => transferring dockerfile: 93B                                                                                                                                                                                             0.0s
 => [internal] load .dockerignore                                                                                                                                                                                               0.0s
 => => transferring context: 2B                                                                                                                                                                                                 0.0s
 => [internal] load build context                                                                                                                                                                                               0.0s
 => => transferring context: 33B                                                                                                                                                                                                0.0s
 => CACHED [1/1] COPY helloworld /                                                                                                                                                                                              0.0s
 => exporting to image                                                                                                                                                                                                          0.0s
 => => exporting layers                                                                                                                                                                                                         0.0s
 => => writing image sha256:c5664c4c93727aae40daca2c1fc0aa13ea2e2c58ba2962fa8d981aa0ec09012e                                                                                                                                    0.0s
 => => naming to docker.io/library/helloworld                                            

Then when I run the container I get the error exec /helloworld: no such file or directory:

$ docker run helloworld
exec /helloworld: no such file or directory

What am I doing wrong? Should I compiled the helloworld in a different mode?

Answer 1

You need to compile at docker build time, e.g.:

FROM ubuntu
RUN apt-get update -y && apt-get install gcc -y
COPY helloworld.c .
RUN gcc -o helloworld helloworld.c
ENTRYPOINT ["./helloworld"]

$ docker build -t helloworld .
$ docker run helloworld
Hello world!