How to view logs / stdout when building an image?

[ole]

When building an image, it looks like container doesn't display the stdout output of the build commands unless an error occurs. I'd like to see this output also for commands that ran successfully.

Question: Is there a way to see the complete stdout/stderr output of the build process, either during or (ideally also) after the build? I looked at the help/arguments for container build, container logs, and container system logs, but if it's possible, I can't figure it out.

Example

Here's a very simple Containerfile:

FROM alpine

RUN echo "Hello from Alpine!"

And here's my build command:

container build --debug --tag test-image --file Containerfile .

(I tried with and without --debug)

This produces output like this:

[+] Building 0.1s (5/5) FINISHED
 => [resolver] fetching image...docker.io/library/alpine                                                                                                0.0s
 => [internal] load .dockerignore                                                                                                                       0.0s
 => => transferring context: 2B                                                                                                                         0.0s
 => oci-layout://docker.io/library/alpine@sha256:25109184c71bdad752c8312a8623239686a9a2071e8825f20acb8f2198c3f659                                       0.0s
 => => resolve docker.io/library/alpine@sha256:25109184c71bdad752c8312a8623239686a9a2071e8825f20acb8f2198c3f659                                         0.0s
 => CACHED [linux/arm64 1/2] RUN echo "Hello from Alpine!"                                                                                              0.0s
 => exporting to oci image format                                                                                                                       0.0s
 => => exporting layers                                                                                                                                 0.0s
 => => exporting manifest sha256:70db5aa51585cad8ee2d460cfbb34905aad1dd36c94ed1a7f8c82a356234863c                                                       0.0s
 => => exporting config sha256:e85f9416f1e001cdbae132e8415b0da393e3bfba2ce9dd5cba49fe6f62e4bf99                                                         0.0s
 => => exporting manifest list sha256:52980ef96e07a560ec6173959f0734c1b4103e868db9193f53cf2742d339c6b1                                                  0.0s
 => => sending tarball                                                                                                                                  0.0s
Successfully built test-image:latest

To reiterate, I'd like some way to see the line "Hello from Alpine!" in the build log, ideally also accessible after building. My goal is to review the output for unexpected messages that might point to omissions in my Containerfile. This would also be a great help in printf-style debugging when trying to figure out why a build fails at a certain step.

Thanks!

[saehejkang]

Try the command below.

container build --debug --tag test-image --file Containerfile . --progress plain --no-cache

I got the output below with the Dockerfile you pasted and it does output the "Hello from Alpine!"

#5 [linux/arm64 1/2] RUN echo "Hello from Alpine!"
#5 0.041 Hello from Alpine!
#5 DONE 0.0s

FWIW there are lots of quality of life updates that need to be made to fix any stdout/stderr outputs for most (if not all) of the commands. So if that is does not 100% accomplish what you are looking for, I can take a deeper look into it.

[ole]

--progress plain does indeed do what I want. Thanks a lot!

FWIW there are lots of quality of life updates that need to be made to fix any stdout/stderr outputs for most (if not all) of the commands. So if that is does not 100% accomplish what you are looking for, I can take a deeper look into it.

I'd generally love to be able to review the stdout/stderr output of a build process after the fact, even if I forget to pass --progress-plain to the build command. Maybe this can be achieved via container logs or container image inspect?

To give you a concrete example why this would be a useful feature for me, I use Swiftly to install a Swift toolchain in one of my images. After installation, the swiftly install command prints a list of recommended system libraries you should install via the system package manager. Since this list can potentially change with new Swift or Swiftly versions, I want to review the output of swiftly install in my image build for any missing packages I should install.

[saehejkang]

I'd generally love to be able to review the stdout/stderr output of a build process after the fact, even if I forget to pass --progress-plain to the build command. Maybe this can be achieved via container logs or container image inspect?

Couple of things you could maybe try (I have not tested this myself).

# follow the system logs in real time
container system logs --follow 

# open a new terminal window and run the build with plain progress
container build --debug --tag test-image --file Containerfile . --progress plain --no-cache

Check the log output and see if anything there is is what you are looking for. Maybe even omit --progress plain and see if that works? As stated before, lots of commands do not have support for stderr/stdout and hopefully we get started on those updates in the near future.