I have a Dockerfile, which ends with:
ENTRYPOINT ["/bin/bash", "/usr/local/cdt-tests/run-tests.sh"]
After building this container, I want to run it, but instead of executing this bash script (run-tests.sh), I want to open up a terminal window inside the container to inspect the filesystem.
If there were no ENTRYPOINT line, I could do this:
docker build -t x .
docker run -it x /bin/bash
and I could examine the container's files.
However, since there is an ENTRYPOINT, then that script will run and I cannot examine the container's files.
Is there anything I can do to get into the container to snoop around?
docker run has an --entrypoint option
Related
Here is my dockerfile
FROM httpd:latest
ENV ENV_VARIABLE "http://localhost:8081"
# COPY BUILD AND CONFIGURATION FILES
COPY entrypoint.sh /
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]
Here is the entrypoint.sh file
#!/bin/bash
sed -i 's,ENV_VARIABLE,'"$ENV_VARIABLE"',g' /path/to/config/file
exec "$#"
To run the container
docker run -e ENV_VARIABLE=some-value <image-name>
The sed command works perfectly fine and the value from environment variable gets reflected in config file. But whenever i start the container the container stops automatically.
I ran the command docker logs to check the logs but logs were empty.
The Dockerfile reference notes:
If CMD is defined from the base image, setting ENTRYPOINT will reset CMD to an empty value. In this scenario, CMD must be defined in the current image to have a value.
So you need to find the CMD from the base image and repeat it in your Dockerfile. Among other places, you can find that on the Docker hub listing of the image history
CMD ["httpd-foreground"]
docker inspect httpd or docker history httpd would also be able to tell you this.
I have a little problem, when i run my container this:
docker run -it emails_request cucumber -t #teste_inserindo_email
It's ok.
But, when i run this:
docker run it emails_request
Where my #teste_inserindo_emails, is on my dockerfile
WORKDIR /app
COPY Gemfile .
RUN bundle install && bundle clean
COPY . /app
EXPOSE 80
RUN cucumber -t #teste_inserindo_email
#CMD ["cucumber", "-t", " #teste_inserindo_email"]
Not found, return:
$ docker run -t emails_request
irb(main):001:0>
Or:
$ docker run emails_request
Switch to inspect mode.
what's your question exactly? you can just run it manually by firing up a container with an interactive terminal from your image, and then run the commands you want, or have a script in the image (or mounted as a volume) and then pass the script as the entry command instead.
docker run -it IMAGE_ID bash (for running manual commands)
if you want to use a script instead, put an ENTRYPOINT script in your Dockerfile instead
I've created a dockerfile with various compile and build tools. The goal of the dockerimage is to standardize our development tools, and make it easy and consistent for developing.
Everything is installed.
What I am stuck on, is how to make the docker container keep running, and be able to have a bash shell to that container so that I can run, for example, make etc. ?
If I use ENTRYPOINT /bin/bash my container exits immediately. How to keep the container running?
You should use the command at run time. You run your Docker container in interatice mode (-i) and set the command to "/bin/bash":
docker run -it myDockerImage myCommandToExecuteInteractively
For instance:
docker run -it myDocker /bin/bash
Here is a real life example:
a) Pulling the most basic image
docker pull debian:jessie-slim
b) Let's have a bash there:
docker run -it debian:jessie-slim /bin/bash
c) Enjoy:
A docker container will run as long as the CMD/Entrypoint from your Dockerfile takes.
You can run your Docker container in interactive mode using switch i
sudo docker run -it --entrypoint=/bin/bash <imagename>
Example : docker run -it --entrypoint=/bin/bash ubuntu:14.04
This will start an interactive shell in your container. Your container will exit as soon as you exit that shell.
There seems to be a difference between how Docker runs commands in a Dockerfile versus running commands manually after starting a container. This seems to be due to the kind of shells you can start, a (I assume) non-interactive shell with a Dockerfile vs an interactive one when running something like docker run -it <some-img-id>.
How can I debug running commands in a Docker container so that it runs exactly like the commands are run from a Dockerfile? Would just adding /bin/bash --noprofile to the run cmd suffice? Or is there anything else different about the environment when started from a Dockerfile?
What you are experiencing is the behavior because of the shell. Most of us are used to using the bash shell. So generally we would attempt to run the commands in the below fashion
For new container
docker run -it <imageid> bash
For existing container
docker exec -it <containerid> bash
But when we specify some command using RUN directive inside a Dockerfile
RUN echo Testing
Then it is equivalent to running /bin/sh -c 'echo Testing'. So you can expect certain differences as both the shells are different.
In Docker 1.12 or higher you have a Dockerfile directive named SHELL this allows you to override the default SHELL
SHELL ["/bin/bash", "-c"]
RUN echo Testing
This would make the RUN command be executed as bash -c 'echo Testing'. You can learn more about the SHELL directive here
Short answer 1:
If Dockerfile don't use USER and SHELL commands, then this:
docker --entrypoint "/bin/sh -c" -u root <image> cmd
Short answer 2:
If you don't squash or compress image after the build, Docker creates images layers for each of the Dockerfile commands. You can see them in the output of docker build at the end of each step with --->:
Step 2/8 : WORKDIR /usr/src/app
---> 5a5964bed25d # <== THIS IS IMAGE ID OF STEP 2
Removing intermediate container b2bc9558e499
Step 3/8 : RUN something
---> f6e90f0a06e2 # <== THIS IS IMAGE ID OF STEP 3
Removing intermediate container b2bc9558e499
Look for the image id just before the RUN step you want to debug (for example you want to debug step 3 on above, take the step 2 image id). Then just run the command in that image:
docker run -it 5a5964bed25d cmd
Long answer 1:
When you run docker run [image] cmd Docker in fact starts the cmd in this way:
Executes the default entrypoint of the image with the cmd as its argument. Entrypoint is stored in the image on build by ENTRYPOINT command in Dockerfile. Ie if cmd is my-app and entrypoint is /bin/sh -c, it executes /bin/sh -c my-app.
Starts it with default user id of the image, which is defined by the last USER command in Dockerfile
Starts it with the environment variables from all ENV commands from image's Dockerfile commulative
When docker build runs the Dockerfile RUN, it does exatly the same, only with the values present at that time (line) of the Dockerfile.
So to be exact, you have to take the value of ENVs and last USER command before your RUN line, and use those in the docker run command.
Most common images have /bin/sh -c or /bin/bash -c as entrypoint and most likely the build operates with root user. Therefore docker --entrypoint "/bin/bash -c" -u root <image> cmd should be sufficient
Is there a way to check if the docker image has all of the files that the Dockerfile copies over and to understand if the image is built as configured in the Dockerfile? My situation is that the image is built successfully, however when I try running it, docker complains that it cant find some file or other and the container fails to run, so I cant exec on it.
Doing docker inspect is not helping since it does not report on the files in the image. Is there some method?
You can run a shell based on that image:
docker run -it <image-name> bash
Use sh instead if there is no bash available. There you can search for files as any shell.
But maybe you have not bash in the image, so use sh:
docker run -it <image-name> sh
But maybe you have an odd entrypoint, so override it:
docker run -it --entrypoint sh <image-name>
You can see the history of file and check if all the required files are present at the time of image creation
docker image history --no-trunc [image_name] > [file_name]