CODEWITHSUNDEEP
docker
Kiran
Kiran

Reputation: 57949

Geting a log of execution of current instructions when doing a 'docker run'

I am a newbie to Docker and I am trying to see if I can get logs for the following instructions when they are getting executed.

FROM ubuntu:16.04

ENV name John

ENTRYPOINT echo "Hello, $name"

My aim here is check how(the path etc.) the shell mode is working in executing the ENV here and also how the ENTRYPOINT is being executed.

I can imagine these kind of logs could be useful in debugging purposes, so probably I am missing something obvious. Any ideas please?

Upvotes: 0

Views: 438

Answers (2)

David Maze
David Maze

Reputation: 158724

The Dockerfile instructions don’t do much; they record some state in fields in the built Docker image. As @BrayanCaldera’s answer indicates, you’ll see these go by in the docker build output, but nothing runs during container build time.

If the ENTRYPOINT is a full-blown script then you can use usual script debugging techniques on it to see what happens when the container starts up. For instance:

#!/bin/sh
# Print out every command as it executes
set -x
# Print out the current environment
env
# Run the actual command
exec "$@"

To tell the Docker image what to do by default when you docker run you should usually use the CMD directive. If you need to do pre-launch setup then an ENTRYPOINT script that uses exec "$@" to run the CMD is a typical path.

Upvotes: 2

Brayan Caldera
Brayan Caldera

Reputation: 2199

For see the logs on terminal you only need to execute this line:

docker build --rm -f dockerfile -t log:latest .

If you need to store these logs in a file you only need to execute this line:

docker build -t logs . > image.log

Upvotes: 0

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