Sure.  Docker is just responding to the error codes returned by the `RUN` shell scripts in the `Dockerfile`.  If your `Dockerfile` has something like:

    RUN make

You could replace that with:

    RUN make; exit 0

This will always return a `0` (success) exit code.  The disadvantage here is that your image will appear to build successfully even if there *are* actual errors in the build process.


This might be of interest to those, whose potential errors in their images are **not harmless enough** *to go unnoticed/logged*. (Also, not enough rep. to comment, so here as an answer.)
 
As pointed out, the disadvantage of `RUN make; exit 0` is you don&#39;t get to know, if your build failed. Hence, rather use something like:

    make test 2&gt;&amp;1 &gt; /where/ever/make.log || echo &quot;There were failing tests!&quot;

Like this, you get notified via the docker image build process log, and you can see what exactly went bad during `make` (or whatsoever else execution, this is not restricted to make).

You can also use the standard bash ignore error `|| true`, which is nice if you are in the middle of a chain:

    RUN &lt;first stage&gt; &amp;&amp; &lt;job that might fail&gt; || true &amp;&amp; &lt;next stage&gt;

I&#39;m following the Flask tutorial here: 

http://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world

I get to the point where I try ./run.py and I get:

    Traceback (most recent call last):
      File &quot;./run.py&quot;, line 3, in &lt;module&gt;
        from app import app
      File &quot;/Users/benjaminclayman/Desktop/microblog/app/__init__.py&quot;, line 1, in &lt;module&gt;
        from flask import Flask
    ImportError: No module named flask

This looks similar to:

[https://stackoverflow.com/questions/24188240/importerror-no-module-named-flask][1]

But their solutions aren&#39;t helpful.  For reference, I *do* have a folder named flask which one user mentioned may cause issues.


  [1]: https://stackoverflow.com/questions/24188240/importerror-no-module-named-flask

Flask ImportError: No Module Named Flask

I learned from my colleague that one can write and execute a C program without writing a `main()` function. It can be done like this:

`my_main.c`

    /* Compile this with gcc -nostartfiles */
    
    #include &lt;stdlib.h&gt;
    
    void _start() {
      int ret = my_main();
      exit(ret); 
    }
 
    int my_main() {
      puts(&quot;This is a program without a main() function!&quot;);
      return 0; 
    }

Compile it with this command:

    gcc -o my_main my_main.c –nostartfiles

Run it with this command:
 
    ./my_main

When would one need to do this kind of thing? Is there any real world scenario where this would be useful?

What is the use of _start() in C?

I&#39;ve got a Dockerfile. When building the image, the build fails on this error:

    automake: error: no &#39;Makefile.am&#39; found for any configure output
    Error build: The command [/bin/sh -c aclocal &amp;&amp; autoconf &amp;&amp; automake -a] returned a non-zero code: 1

which in reality is harmless. The library builds fine, but Docker stops the build once it receives this error. Is there any way I can instruct Docker to just ignore this?

Dockerfile build - possible to ignore error?

I've got a Dockerfile. When building the image, the build fails on this error:
<pre><code class="hljs language-typescript">automake: error: no 'Makefile.am' found for any configure output
Error build: The command [/bin/sh -c aclocal &#x26;&#x26; autoconf &#x26;&#x26; automake -a] returned a non-zero code: 1
</code></pre>
which in reality is harmless. The library builds fine, but Docker stops the build once it receives this error. Is there any way I can instruct Docker to just ignore this?

This is an error message I get when building a Docker image:
```
Step 18 : RUN mkdir /var/www/app &amp;&amp; chown luqo33:www-data /var/www/app
---&gt; Running in 7b5854406120 mkdir: cannot create directory &#39;/var/www/app&#39;: No such file or directory
```
This is a fragment of Dockerfile that causes the error:

    FROM ubuntu:14.04
    RUN groupadd -r luqo33 &amp;&amp; useradd -r -g luqo33 luqo33

    &lt;installing nginx, fpm, php and a couple of other things&gt;

    RUN mkdir /var/www/app &amp;&amp; chown luqo33:www-data /var/www/app
    VOLUME /var/www/app
    WORKDIR /var/www/app


`mkdir: cannot create directory &#39;/var/www/app&#39;: No such file or directory` sound so nonsensical - of course there is no such directory. I want to create it. What is wrong here?

Cannot execute RUN mkdir in a Dockerfile

Currently i am starting RabbitMQ Docker container using the default RabbitMQ image from [DockerHub][1]. Using the following commands.

    docker run --restart=always \
    -d \
    -e RABBITMQ_NODENAME=rabbitmq \
    -v /opt/docker/rabbitmq/data:/var/lib/rabbitmq/mnesia/rabbitmq \
    -p 5672:5672 \
    -p 15672:15672 \
    --name rabbitmq rabbitmq:3-management

I have a need where i want to provide defaults users / and virtual-hosts when the image is first started. For example to create a default &#39;test-user&#39;.

Currently i have to do that manually by using the management plugin and adding the users / virtual-hosts via the web ui. Is there a way i can provide default settings when starting the RabbitMQ image?

  [1]: https://registry.hub.docker.com/_/rabbitmq/

How to add initial users when starting a RabbitMQ Docker container?

I am unable to remove the dead container, it appears again after i restart the Docker service.

    docker ps -a
    CONTAINER ID         STATUS          
    11667ef16239         Dead

Then

    docker rm -f 11667ef16239

Then, when I ran the docker ps -a, no docker containers showing.  

    docker ps -a
    CONTAINER ID         STATUS

However, when I restart the docker service:

    service docker restart

And run the docker ps -a again:

    docker ps -a
    CONTAINER ID         STATUS          
    11667ef16239         Dead

Docker - Cannot remove dead container

I am a Java developer. We use Weblogic to host our applications. I have been told to look into replacing weblogic with an opensource alternative. We are planning use with SpringBoot. We are also looking at Docker/Cloud Foundry. However Docker/Cloud Foundry is new territory for me.

 1. Can someone please tell me the difference between Cloud Foundry and Docker?
 2. If we use Docker but not Cloud foundry, what are we missing out on?
 3. If we use Cloud Foundry but not Docker, what are we missing out on?

Thank you for your help. 

What is the difference between Cloud Foundry and Docker?

I&#39;m using the [official Postgres Docker image](https://registry.hub.docker.com/_/postgres/) trying to customize its configuration. For this purpose, I use the command `sed` to change `max_connections` for example: 

    sed -i -e&quot;s/^max_connections = 100.*$/max_connections = 1000/&quot; /var/lib/postgresql/data/postgresql.conf

I tried two methods to apply this configuration. The first is by adding the commands to a script and copying it within the init folder &quot;/docker-entrypoint-initdb.d&quot;. The second method is by running them directly within my Dockerfile with &quot;RUN&quot; command (this method worked fine with a non-official Postgresql image with a different path to the configuration file &quot;/etc/postgres/...&quot;). In both cases the changes fail because the configuration file is missing (I think it&#39;s not created yet).

How should I change the configuration?

Edit 1:

Here is the Dockerfile used to create the image:

    # Database (http://www.cs3c.ma/)

    FROM postgres:9.4
    MAINTAINER Sabbane &lt;contact@cs3c.ma&gt;

    ENV TERM=xterm

    RUN apt-get update
    RUN apt-get install -y nano

    ADD scripts /scripts
    # ADD scripts/setup-my-schema.sh /docker-entrypoint-initdb.d/

    # Allow connections from anywhere.
    RUN sed -i -e&quot;s/^#listen_addresses =.*$/listen_addresses = &#39;*&#39;/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN echo &quot;host    all    all    0.0.0.0/0    md5&quot; &gt;&gt; /var/lib/postgresql/data/pg_hba.conf

    # Configure logs
    RUN sed -i -e&quot;s/^#logging_collector = off.*$/logging_collector = on/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_directory = &#39;pg_log&#39;.*$/log_directory = &#39;\/var\/log\/postgresql&#39;/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_filename = &#39;postgresql-\%Y-\%m-\%d_\%H\%M\%S.log&#39;.*$/log_filename = &#39;postgresql_\%a.log&#39;/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_file_mode = 0600.*$/log_file_mode = 0644/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_truncate_on_rotation = off.*$/log_truncate_on_rotation = on/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_rotation_age = 1d.*$/log_rotation_age = 1d/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_min_duration_statement = -1.*$/log_min_duration_statement = 0/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_checkpoints = off.*$/log_checkpoints = on/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_connections = off.*$/log_connections = on/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_disconnections = off.*$/log_disconnections = on/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^log_line_prefix = &#39;\%t \[\%p-\%l\] \%q\%u@\%d &#39;.*$/log_line_prefix = &#39;\%t \[\%p\]: \[\%l-1\] user=\%u,db=\%d&#39;/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_lock_waits = off.*$/log_lock_waits = on/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#log_temp_files = -1.*$/log_temp_files = 0/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#statement_timeout = 0.*$/statement_timeout = 1800000        # in milliseconds, 0 is disabled (current 30min)/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^lc_messages = &#39;en_US.UTF-8&#39;.*$/lc_messages = &#39;C&#39;/&quot; /var/lib/postgresql/data/postgresql.conf

    # Performance Tuning
    RUN sed -i -e&quot;s/^max_connections = 100.*$/max_connections = 1000/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^shared_buffers =.*$/shared_buffers = 16GB/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#effective_cache_size = 128MB.*$/effective_cache_size = 48GB/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#work_mem = 1MB.*$/work_mem = 16MB/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#maintenance_work_mem = 16MB.*$/maintenance_work_mem = 2GB/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#checkpoint_segments = .*$/checkpoint_segments = 32/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#checkpoint_completion_target = 0.5.*$/checkpoint_completion_target = 0.7/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#wal_buffers =.*$/wal_buffers = 16MB/&quot; /var/lib/postgresql/data/postgresql.conf
    RUN sed -i -e&quot;s/^#default_statistics_target = 100.*$/default_statistics_target = 100/&quot; /var/lib/postgresql/data/postgresql.conf


    VOLUME [&quot;/var/lib/postgresql/data&quot;, &quot;/var/log/postgresql&quot;]

    CMD [&quot;postgres&quot;]

With this Dockerfile the build process shows the error: `sed: can&#39;t read /var/lib/postgresql/data/postgresql.conf: No such file or directory`


How to customize the configuration file of the official PostgreSQL Docker image?

I am working on a task that involves building a docker image with **centOs** as its base using a **Dockerfile** . One of the steps inside the dockerfile needs **http_proxy** and **https_proxy** ENV variables to be set in order to work behind the proxy. 

As this Dockerfile will be used by multiple teams having different proxies, I want to avoid having to edit the Dockerfile for each team.  Instead I am looking for a solution which allows me to pass ENV variables at build time, e.g.,

&gt;sudo docker build -e http_proxy=somevalue .

I&#39;m not sure if there is already an option that provides this.  Am I missing something? 

Can we pass ENV variables through cmd line while building a docker image through dockerfile?

I want to build my PHP-FPM image with `php-redis` extension based on the [official PHP Docker image](https://registry.hub.docker.com/_/php/), for example, using this Dockerfile: [php:5.6-fpm](https://github.com/docker-library/php/blob/a413eb0123d10321928696ffea7442bed7dc0dc7/5.6/fpm/Dockerfile).

The docs say that I can install extensions this way, installing dependencies for extensions manually: 

    FROM php:5.6-fpm
    # Install modules (iconv, mcrypt and gd extensions)
    RUN apt-get update &amp;&amp; apt-get install -y \
            libfreetype6-dev \
            libjpeg62-turbo-dev \
            libmcrypt-dev \
            libpng12-dev \
        &amp;&amp; docker-php-ext-install iconv mcrypt \
        &amp;&amp; docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ \
        &amp;&amp; docker-php-ext-install gd
    CMD [&quot;php-fpm&quot;]

Without Docker I installed it with `apt-get install php5-redis`. But how can I install it using the approach above?


How to install php-redis extension using the official PHP Docker image approach?

Inside of my Dockerfiles I would like to COPY a file into my image if it exists, the requirements.txt file for pip seems like a good candidate but how would this be achieved?

    COPY (requirements.txt if test -e requirements.txt; fi) /destination
    ...
    RUN  if test -e requirements.txt; then pip install -r requirements.txt; fi
or

    if test -e requirements.txt; then
        COPY requiements.txt /destination;
    fi
    RUN  if test -e requirements.txt; then pip install -r requirements.txt; fi

Conditional COPY/ADD in Dockerfile?

_What I want to do is build a docker image for my Java application but the following considerations should be true for most compiled languages._

# problem
On my build server I want to produce a docker image for my application as the deliverable. For this I have to compile the application using some build tool (typically Gradle, Maven or Ant) and then add the created JAR file to the docker image. As I want the docker image to just execute the JAR file I will of course start from a base image with Java already installed.

# There are three ways of doing this:

## let the build tool control the process
In this case my build tool controls the whole process. So it prepares the JAR file and after the JAR is created it calls Docker to create the image. This works as the JAR is created beforehand and Docker can be  oblivious of the build process needed to create the JAR.

But my Dockerfile is no longer standalone. It depends on steps to happen outside of Docker for it work. In my Dockerfile I will have a `COPY` or `ADD` statement that is supposed to copy the JAR file to the image. This statement will fail when the jar is not created beforehand. So just executing the Dockerfile might not work. This becomes a problem if you want to integrate with services that just build using the present Dockerfile like the auto-build feature on DockerHub.

## let Docker control the build
In this case all necessary steps to create the image are added to the Dockerfile so the image can be created by just executing the Docker build.

The main problem with this approach is that there is no way to add to a Dockerfile commands that should be executed outside the docker image being created. This means I have to add my source code and my build tools to the docker image and build my JAR file inside the image. This will result in my image being bigger than it has to be due to all the files added that will be unnecessary at runtime. This will also add extra layers to my image.

### Edit:
As @adrian-mouat pointed out if I would add the sources, build the application and deleted the sources in one RUN statement I could avoid adding unnecessary files and layers to the Docker image. This would mean creating some insane chained command. 

## two separate builds
In this case we split our build in two: first we create the JAR file using our build tool and upload it to a repository (Maven or Ivy repository). We then trigger a separate Docker build that just adds the JAR file from the repository.

# conclusion
In my opinion the better way would be _letting the build tool control the process_. This is will result in a clean docker image and as the image is what we want to deliver this is of importance. To avoid having a potentially not working Dockerfile lying around this should be created as part of the build. So no one would accidentally use it to start a broken build.

But this will not allow me to integrate with DockerHub.

# question
Is there another way I am missing?

# update June 2020
In the years since I first created this question a lot of stuff has changed. At this point I would advocate using [Googel&#39;s JIB Tool](https://github.com/GoogleContainerTools/jib). It integrates with the most common Java Build Tools (Maven and Gradle) and allows you to create container directly from your build. This is much more concise than any of the old approaches I considered all these years ago.

# update February 2021
I found this blog post and video from James Ward that reflects better what is currently state of the art.
https://cloud.google.com/blog/topics/developers-practitioners/comparing-containerization-methods-buildpacks-jib-and-dockerfile

How to build a docker container for a Java application

Yet another Docker symlink question. I have a bunch of files that I want to copy over to all my Docker builds. My dir structure is:

    parent_dir
        - common_files
            - file.txt
        - dir1
            - Dockerfile  
            - symlink -&gt; ../common_files

In above example,  I want file.txt to be copied over when I docker build inside dir1. But I don&#39;t want to maintain multiple copies of file.txt. 
Per [this link, as of docker version 0.10][1], docker build must 

&gt; Follow symlinks inside container&#39;s root for ADD build instructions.


  [1]: https://github.com/docker/docker/blob/master/CHANGELOG.md#0100-2014-04-08

But I get **no such file or directory** when I build with either of these lines in my Dockerfile: 

`ADD symlink /path/dirname` or
`ADD symlink/file.txt /path/file.txt`


mount option will NOT solve it for me (cross platform...).
I tried `tar -czh . | docker build -t` without success.

Is there a way to make Docker follow the symlink and copy the common_files/file.txt into the built container?



Content Type	Original Author	Original Content on Stackoverflow
Question	Oskar	View Question on Stackoverflow
Solution 1 - Docker	larsks	View Answer on Stackoverflow
Solution 2 - Docker	mths	View Answer on Stackoverflow
Solution 3 - Docker	MortenB	View Answer on Stackoverflow

Dockerfile build - possible to ignore error?

Docker Problem Overview

Docker Solutions

Solution 1 - Docker

Solution 2 - Docker

Solution 3 - Docker

What is the use of _start() in C?

Flask ImportError: No Module Named Flask

Attributions