Docker create/start and --interactive option

[goofyfranklin (Antonio Cota)]

1. Is it correct to say that docker container create --interactive ubuntu is equal to docker container create -a STDIN -a STDOUT -a STDERR --interactive ubuntu?
2. Is it correct to say that docker container start --interactive <container ID> is equal to docker container start --interactive --attach <container ID>?

I tested the following commands docker container create --interactive --name u8 ubuntu and docker container start --interactive u8 and I can properly interact with the bash shell.

[meyay (Metin Y.)]

You can check container configurations like this:

docker inspect --format '{{json .Config}}' <container name or id>

Replace <container name or id> with the name of a container or its id. You might want to pipe the result to jq to have a nice formatted output.

You can create all the variations you want, inspect their config and compare the resulting configs.

I am aware this does not directly answer your questions. It does something better: it shows you, how you can answer your questions yourself.

[rimelek (Ákos Takács)]

I also had some tests here:

Understanding docker run --attach option

I can’t say that I know everythng about these parameters, but extending @meyay’s answer here is what I think can help you to understand a little bit better what these parameters are for. Docker has a client-server architecture. The Docker client is just communicating with the server and tells the server to run a container. The standard input, standard error and standard output streams are still on the server. Normally you wouldn’t see the output or error messages and you wouldn’t be able to run…

Understanding docker run --attach option

My point was that the command is not running on your client. The container is running on the server so the command is running on the server too in a container. Of course if you are not using Docker Desktop or any other remote docker daemon, your client is the server. The container is just isolation and resouce limits. The process “thinks” it is running on a separate machine but it is still running on the host isolated from the rest of the environment. When I saw @meyay’s post I…

In short, -a or --attach means you attach to standard sreams which will happen by default unless passing -d or --detach, so yes to the question 1., but docker start or docker container start by default will not attach to STDIN as it also menitoned in the output of docker start --help

  -a, --attach               Attach STDOUT/STDERR and forward signals

But it is true, that @meyay gave you a way to check the config even if the behaviour changes in the future. Currently you can also use this command as well to get the the values of the relevant parameters:

docker inspect <container name or id> | grep -A5 AttachStdin

But it may not work in the future if the structure of the config changes.

[goofyfranklin (Antonio Cota)]

Thanks both. Following your suggestions I can conclude that:

1. docker container create --interactive is equal to docker container create -a STDIN -a STDOUT -a STDERR --interactive
2. docker container start --interactive is not properly equal to docker container start --interactive --attach, since, as far as I understood, with docker container start --interactive STDOUT/STDERR is attached after sending the first input.