//=== https://docs.docker.com/engine/reference/run
$ docker run -d ... (detached mode, run in background?)
$ docker run -t ... (run in foreground)
Detached (-d)
To start a container in detached mode, you use -d=true or just -d option. By design, containers started in detached mode exit when the root process used to run the container exits, unless you also specify the --rm option. If you use -d with --rm, the container is removed when it exits or when the daemon exits, whichever happens first.
Do not pass a service x start command to a detached container. For example, this command attempts to start the nginx service.
$ docker run -d -p 80:80 my_image service nginx start
This succeeds in starting the nginx service inside the container. However, it fails the detached container paradigm in that, the root process (service nginx start) returns and the detached container stops as designed. As a result, the nginx service is started but could not be used. Instead, to start a process such as the nginx web server do the following:
$ docker run -d -p 80:80 my_image nginx -g 'daemon off;'
To do input/output with a detached container use network connections or shared volumes. These are required because the container is no longer listening to the command line where docker run was run.
To reattach to a detached container, use docker attach command.
Foreground
In foreground mode (the default when -d is not specified), docker run can start the process in the container and attach the console to the process’s standard input, output, and standard error. It can even pretend to be a TTY (this is what most command line executables expect) and pass along signals. All of that is configurable:
-a=[] : Attach to `STDIN`, `STDOUT` and/or `STDERR`
-t : Allocate a pseudo-tty
--sig-proxy=true: Proxy all received signals to the process (non-TTY mode only)
-i : Keep STDIN open even if not attached
If you do not specify -a then Docker will attach to both stdout and stderr . You can specify to which of the three standard streams (STDIN, STDOUT, STDERR) you’d like to connect instead, as in:
$ docker run -a stdin -a stdout -i -t ubuntu /bin/bash
For interactive processes (like a shell), you must use -i -t together in order to allocate a tty for the container process. -i -t is often written -it ,,,
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