Why can't the file be found after copying it to the container?

php Xiaobian Yuzai may encounter a common problem when using container technology: files cannot be found after they are copied to the container. This problem usually occurs when using containerization platforms such as Docker. The reason may be that the file path is set incorrectly, or the file system inside the container is inconsistent with the host. There are many ways to solve this problem, such as using an absolute path or copying the file into the container through a shared folder. Before solving this problem, we need to first understand the mapping relationship between the container's file system and file path, and how to correctly configure the file path.

Question content

I have a dockerfile as shown below:

from golang:1.19 as builder
workdir /app
copy . .
run cgo_enabled=0 go build -v -o "hello-bin"


#from scratch
from alpine
copy --from=builder /app/hello-bin /app/hello-bin
copy --from=builder /app/start.sh /app/start.sh
workdir /app
entrypoint  [ "./start.sh" ]

It just builds a binary from the hello-world go file. However, when I try to run this container with the following docker-compose settings, it says exec ./start.sh: no such file or directory.

version: "3"

services:
  hello:
    restart: always
    build:
      context: .
      dockerfile: dockerfile

The directory structure is

❯ tree .
.
├── dockerfile
├── docker-compose.yaml
├── go.mod
├── hello
├── init.go
└── start.sh

Therefore start.sh should be loaded into the builder<code> container via copy. The same goes for the . line, which should be passed to the second container via copy --from=builder /app/start.sh /app/start.sh.

Context, the contents of start.sh are as follows:

#!/bin/bash

_main() {
  echo "start"
}

_main "$@"

The part that confuses me the most is that if I change it in the dockerfile to cmd [ "ls", "-l" ] it will actually print out

awesomeproject3-hello-1  | -rwxr-xr-x    1 root     root       1819562 May 19 02:41 hello-bin
awesomeproject3-hello-1  | -rwxrwxrwx    1 root     root            51 May 19 02:39 start.sh

If I change it to entrypoint [ './hello-bin' ] in the dockerfile, the binary also runs successfully. I just don't understand why it says there is no ./start.sh.

Update: Inspired by @larsks, I noticed that if I change the header of ./start.sh from #!/bin/bash to # !/bin/sh and it will work magically. I'm still confused what is the underlying issue here, how should I fix the docker file if I want to keep the bash headers?

Solution

The error occurs because you used #!/bin/bash in start.sh.

The Alpine docker image does not have bash installed by default. It uses the Busybox shell instead.

You can install bash in a container. See Docker: How to use bash with Alpine based docker image?

Or you can change #!/bin/bash to #!/bin/sh as mentioned in your question comments.

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