Why is docker build not showing any output from commands? - docker

Question

Snippet from my Dockerfile:
FROM node:12.18.0
RUN echo "hello world"
RUN psql --version
When I run docker build . I don't see any output from these two commands even if they are not cached. The documentation says that docker build is verbose by default. Why am I not seeing the output from commands? I used to see them before.
The output while building:
=> [7/18] RUN echo "hello world" 0.9s
The output I am seeing after building finishes:
=> CACHED [6/18] RUN apt-get install postgresql -y 0.0s
=> [7/18] RUN echo "hello world" 6.4s
=> [8/18] RUN psql --version 17.1s
The Dockerfile is created from node:12.18.0 which is based on Debian 9.
Docker version 19.03.13, build 4484c46d9d.

Answer 1

The output you are showing is from buildkit, which is a replacement for the classic build engine that docker ships with. You can adjust output from this with the --progress option:
--progress string Set type of progress output (auto, plain, tty). Use plain to show container output
(default "auto")
Adding --progress=plain will show the output of the run commands that were not loaded from the cache. This can also be done by setting the BUILDKIT_PROGRESS variable:
export BUILDKIT_PROGRESS=plain
If you are debugging a build, and the steps have already been cached, add --no-cache to your build to rerun the steps and redisplay the output:
docker build --progress=plain --no-cache ...
If you don't want to use buildkit, you can revert to the older build engine by exporting DOCKER_BUILDKIT=0 in your shell, e.g.:
DOCKER_BUILDKIT=0 docker build ...
or
export DOCKER_BUILDKIT=0
docker build ...

Answer 2

Just use this flag --progress=plain after build.
For example:
docker-compose build --progress=plain <container_name>
OR
docker build --progress=plain .
If you don't want to use this flag every time, then permanently tell docker to use this flag by doing:
export BUILDKIT_PROGRESS=plain
Here is the official documentation when you type docker build --help.
--progress string Set type of progress output (auto, plain, tty). Use plain to show container output (default "auto")

Answer 3

In Docker 20.10 i had to use the --no-cache flag, too. Otherwise cached output is not shown.
docker build --progress=plain --no-cache .

Answer 4

As an alternative to specifying the --progress=plain option, you can also permanently disable the "pretty" output by setting this env variable in your shell config:
export BUILDKIT_PROGRESS=plain

Answer 5

Do 2 things
Instead of docker build . use this
docker build . --progress=plain
Add random junk to your RUN command every build (this tricks docker into thinking it hasn't seen the command before, so it doesn't use the cached version)
Example. If your command is RUN ls use this instead RUN ls && echo sdfjskdflsjdf (change the sdfjskdflsjdf to something else each time you build).
Why this works
I tried other answers and they all presented problems and imperfections. It's highly frustrating that Docker doesn't have some simple functionality like --verbose=true.
Here's what I ended up using (it's ludicrous but it works).
Suppose you want to see the output of ls command, this won't work docker build .
RUN ls
but this will print the output docker build --progress=plain:
RUN ls
now try again, it won't print! - that's because docker caches the unchanged layer, so the trick is to alter the command each time by adding some nonsense to it && echo sdfljsdfljksdfljk, and changing the nonsense each time docker build --progress=plain:
# This prints
RUN ls && echo sdfljsdfljksdfljk
# Next time you run it use a different token
RUN ls && echo sdlfkjsldfkjlskj
So each and every time, I mash the keyboard and come up with a new token. Stupifying. (note that I tried something like && openssl rand -base64 12 to generate a random string, but docker realises the code hasn't changed that doesn't work).
This solution is highly inferior to genuine docker support for printing output to console.

Answer 6

If your error looks something like this:
#7 0.584 /bin/sh: 1: /install.sh: not found
it's telling you the error is in line number 1. you are running into windows line endings
I was using VS code and I solved it pretty easily by converting the file from CRLF to LF using VS code.
just click on the CRLF button in the bottom right corner of the editor and save the file.
everything should work fine when you build the image now.