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Added note about process interaction with container in detached mode

Signed-off-by: Dharmit Shah <shahdharmit@gmail.com>

Added note about process interaction with container in detached mode

Signed-off-by: Dharmit Shah <shahdharmit@gmail.com>

Dharmit Shah authored on 2015/08/23 21:38:50
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@@ -87,12 +87,30 @@ default foreground mode:
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 ### Detached (-d)
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-In detached mode (`-d=true` or just `-d`), all I/O should be done
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-through network connections or shared volumes because the container is
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-no longer listening to the command line where you executed `docker run`.
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-You can reattach to a detached container with `docker`
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-[*attach*](/reference/commandline/attach). If you choose to run a
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-container in the detached mode, then you cannot use the `--rm` option.
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+To start a container in detached mode, you use `-d=true` or just `-d` option. By
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+design, containers started in detached mode exit when the root process used to
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+run the container exits. A container in detached mode cannot be automatically
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+removed when it stops, this means you cannot use the `--rm` option with `-d` option.
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+
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+Do not pass a `service x start` command to a detached container. For example, this
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+command attempts to start the `nginx` service.
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+
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+    $ docker run -d -p 80:80 my_image service nginx start
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+
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+This succeeds in starting the `nginx` service inside the container. However, it
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+fails the detached container paradigm in that, the root process (`service nginx
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+start`) returns and the detached container stops as designed. As a result, the
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+`nginx` service is started but could not be used. Instead, to start a process
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+such as the `nginx` web server do the following:
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+
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+    $ docker run -d -p 80:80 my_image nginx -g 'daemon off;'
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+
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+To do input/output with a detached container use network connections or shared
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+volumes. These are required because the container is no longer listening to the
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+command line where `docker run` was run.
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+
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+To reattach to a detached container, use `docker`
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+[*attach*](/reference/commandline/attach) command.
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 ### Foreground
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