These are the first 2 lines of a Dockerfile:
FROM node:12
WORKDIR /code
Here are some things I don't understand:
From docker's documentation I know that the 2nd line sets the working directory to /code.
Where does this process occur?
Does it happen when docker runs the second line of the Dockerfile, while creating the image?
If /code doesn't exist, does it get created by docker?
Where will /code be created? In the root directory of the image?
The Dockerfile WORKDIR directive
... sets the working directory.... If the WORKDIR doesn’t exist, it will be created even if it’s not used in any subsequent Dockerfile instruction.
I occasionally see SO questions that RUN mkdir a directory before switching WORKDIR to it. Since WORKDIR will create the directory, this isn't necessary.
All paths in a Dockerfile are always inside the image, except for the source paths for COPY and ADD instructions, which are inside the build context directory on the host. Absolute paths like /code will be directly inside the root directory in the image, following normal Unix conventions.
You can run temporary containers off of your image to examine this, even if the Dockerfile isn't complete yet.
host$ docker build -t my-image .
host$ docker run --rm my-image ls -l /
host$ docker run --rm -it my-image /bin/sh
0123456789ab# ls -l /
0123456789ab# exit
(This will always work, assuming the image includes core tools like sh and ls. docker exec requires the container to be running first; while you're refining the Dockerfile this may not be possible yet.)
The Workdir /path will be created inside the container.
To test this you can do sh into your container.
Steps:
docker exec -it <container-id> sh
ls (Here you will see WORKDIR)
If you want to view the intermediate image layers from your custom image
docker image inspect < image-name >
The default WORKDIR driectory if this is not specified, is the / directory.
More info at the following link,
https://www.geeksforgeeks.org/docker-workdir-instruction/
Related
A simple bash script whereby a user can search through a folder and organise their files by type. For this I need to give my container access to my C drive and navigate to the right directory where the code is executed and where the folders are.
Since it s windows I know I need to use winpty and use \ rather than / when navigating.
winpty docker run -it -v basic-vol:/C:\Users\XYZ\dev\repos\filefind filefind:latest
I am not sure why this is not working. Here is my Dockerfile too:
FROM ubuntu
RUN chmod 700 .
WORKDIR /app
COPY . .
VOLUME [ "/c/Users/XYZ/dev/repos/"]
#when conatiner starts what is the executable
ENTRYPOINT ["/bin/bash", "file-find.sh"]
Would love your help here folks
I am a newbie in Docker. I introduced the Docker environment in WSL2 (Windows10Home). I do not wish to use the VSCode for simpler implementation. I would like to rather use the Ubuntu terminal. When I try to compile my LaTeX file (my_input.tex) with a Docker image (https://hub.docker.com/r/weichuntsai/texlive-small), but it complains that there is no such a tex file.
docker run --name mylatex -dt -v /home/myname:/home weichuntsai/texlive-small:1.1.0
When I send the following command in the terminal, he complains of no corresponding file.
txrun my_input.tex xelex, although I created this tex file in the home
(~, or home/myname) directory.
Sending ls returns tex.mf only without showing my_input.tex unfortunately.
Sending pwd returns root with some reasons. I have no idea why it returns root, not home/myname.
It may be due to my insufficient understanding of Docker, but I appreciate your kind advice on
that question.
N.B. I became to know that Docker images are located in /var/lib/docker.
To change this directory, one must stop the Docker daemon with
sudo service docker stop. Then one must edit /etc/docker/daemon.json.
{
"data-root": "/to/some/path"
}
Checking Dockerfile of your image shows that working directory is root https://hub.docker.com/r/weichuntsai/texlive-small/dockerfile
Just mount your home to container root:
docker run --name mylatex -dt -v /home/myname:/root weichuntsai/texlive-small:1.1.0
OR inside container change to home by cd /home
Checking Dockerfile of your image shows that working directory is root https://hub.docker.com/r/weichuntsai/texlive-small/dockerfile
Just mount your home to container root:
docker run --name mylatex -dt -v "/home/me":"/file" weichuntsai/texlive-small:1.1.0
OR inside container change to home by cd /home
and then you access your file like
docker exec -it mylatex bash
cd /file
ls
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 am a docker beginner. I have used this SO post to run a shell script with docker run and this works fine. However, what I am trying to do is to apply my shell script to a file that lives in my current working directory, where Dockerfile and script are.
My shell script - given a file as an argument, return its name and the number of lines:
#!/bin/bash
echo $1
wc -l $1
Dockerfile:
FROM ubuntu
COPY ./file.sh /
CMD /bin/bash file.sh
then build and run:
docker build -t test .
docker run -ti test /file.sh text_file
This is what I get:
text_file
wc: text_file: No such file or directory
I'm left clueless why the second line doesn't work, why the file can't be found. I don't want to copy my text_file to the container. Ideally, I'd like to run my script from docker container on any file in my current working directory.
Any help will be much appreciated.
Thanks!!
You're building your Docker image containing the script /file.sh. Still, your Docker container does not contain (or know) about the file text_file which you're passing as an argument.
In order to make it known to your Docker container, you have to mount it when running the container.
docker run --rm -it -v "$PWD"/text_file:/text_file test /file.sh /text_file
In order to check for other files, you just have to swap text_file in both the mount and the argument.
Notes
In addition to Docker volume mounts, I might suggest some more improvements to spice up your image.
In order to run a script, you don't have to use ubuntu as your base image. You might be fine with alpine or even more focused bash. And don't forget to use tags in order to enforce the exact same behavior over time.
You can set your script as an ENTRYPOINT of your Dockerfile. Then, your only specifying the script name (text_file in that case) as your command.
When mounting files, you can change the name of the file in your container. Therefore, you can simplify your script and just mounting the file to test at the exact same place every time you run the container.
FROM alpine:3.10
WORKDIR /tmp
COPY file.sh /usr/local/bin/wordcount
ENTRYPOINT /usr/local/bin/wordcount
CMD file
Then,
docker run --rm -it -v "PWD"/text_file:/tmp/file test
will do the job.
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]