ENTRYPOINT

Dockerfile - line 3

ENTRYPOINT [ "/hello.sh" ]

The ENTRYPOINT instruction lets you configure a container that will run as as an executable. Every time you launch a container using this image, the container will run the program specified in ENTRYPOINT, and any options you provide when launching will be passed as arguments to the program.

Any mandatory command-line arguments for the the process should be specified after the program name. If specified, mandatory arguments will not be overridden by any explicitly supplied arguments when launching a container using this image.

For example:

exec form

ENTRYPOINT ["executable", "param1", "param2"]

shell form

ENTRYPOINT command param1 param2

Always use the exec form. There are significant disadvantages to using the shell form, discussed here. In a nutshell, you want your process to run as PID 1 so that it can receive standard UNIX signals, particularly SIGTERM(the conventional termination request signal) and SIGINT (triggered by CTRL-C).

Optional arguments

Any optional command-line arguments that you would like to supply to the ENTRYPOINT process by default should be added to a CMD instruction. These will be appended to the list of any of mandatory arguments you specify with the ENTRYPOINT instruction. However, optional arguments will be overridden by any explicitly supplied arguments when launching a container using this image.

The CMD instruction can be used by itself, not just to augment the ENTRYPOINT instruction, but to replace it. This is useful for launching containers where it's desirable to run different processes bundled in the image. When used this way, the first argument for the CMD instruction must be the program to run, not one of the program options.

When launching a container, any supplied arguments will replace the entire CMD (which, of course, means the first argument in this case must be the name of the program to run, followed by any other arguments).