Docker - Entrypoint (Main)

Language - (Main|Application Entry point) in Docker.

The entry point script is the script called when creating a container from an image with the docker run command

The entrypoint is specified in a dockerfile.

docker run --entrypoint /script.sh repo/image

where: Docker - docker run (Creating a container)

The default entrypoint is specified in the dockerfile. See Doc entrypoint

It has two different behavior that depends of the assignment format. ENTRYPOINT has the following forms:

# exec form, preferred
ENTRYPOINT ["executable", "param1", "param2"] 
# or shell form
ENTRYPOINT command param1 param2 
# or
ENTRYPOINT ["python"]
CMD ["myPythonFile.py"]

Command line arguments to docker run will be appended after all elements in an exec form ENTRYPOINT, and will override all elements specified using CMD.

The shell form prevents any command line arguments (cmd or via run) from being used.

The ENTRYPOINT will be started as a subcommand of /bin/sh -c, which does not pass signals. This means that the executable will not be the container’s PID 1 - and will not receive Unix signals - so your executable will not receive a SIGTERM from docker stop <container>.

docker inspect --format "{{range .Config.Entrypoint}}{{.}}{{end}}" containerName

See Docker - Inspect

When you run docker like this:

docker run -i -t ubuntu bash 

• the image is ubuntu
• the entrypoint is the default /bin/sh -c because there is no ENTRPOINT in the ubuntu dockerfile
• and the command is bash.

The below script start a process before starting the command given at the command line.

It's a wrapper around the default entrypoint.

#!/usr/bin/env bash

echo Starting the ssh-agent for convenience
eval `ssh-agent`

# Start the passed command ($*)
/bin/sh -c "$*"