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Address feedback from @jamtur01. 

Docker-DCO-1.1-Signed-off-by: Andy Rothfusz <github@developersupport.net> (github: metalivedev)
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Andy Rothfusz 2014-01-28 17:32:05 -08:00 committed by Tibor Vass
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docs/sources/reference/run.rst
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@ -21,6 +21,7 @@ Every one of the :ref:`example_list` shows running containers, and so
here we try to give more in-depth guidance.
.. contents:: Table of Contents
:depth: 2
.. _run_running:
@ -37,24 +38,33 @@ To learn how to interpret the types of ``[OPTIONS]``, see
The list of ``[OPTIONS]`` breaks down into two groups:
* options that define the runtime behavior or environment, and
* options that override image defaults.
1. Settings exclusive to operators, including:
Since image defaults usually get set in :ref:`Dockerfiles
<dockerbuilder>` (though they could also be set at :ref:`cli_commit`
time too), we will group the runtime options here by their related
Dockerfile commands so that it is easier to see how to override image
defaults and set new behavior.
* Detached or Foreground running,
* Container Identification,
* Network settings, and
* Runtime Constraints on CPU and Memory
* Privileges and LXC Configuration
We'll start, though, with the options that are unique to ``docker
run``, the options which define the runtime behavior or the container
environment.
2. Setting shared between operators and developers, where operators
can override defaults developers set in images at build time.
.. note:: The runtime operator always has final control over the
behavior of a Docker container.
Together, the ``docker run [OPTIONS]`` give complete control over
runtime behavior to the operator, allowing them to override all
defaults set by the developer during ``docker build`` and nearly all
the defaults set by the Docker runtime itself.
Detached or Foreground
======================
Operator Exclusive Options
==========================
Only the operator (the person executing ``docker run``) can set the
following options.
.. contents::
:local:
Detached vs Foreground
----------------------
When starting a Docker container, you must first decide if you want to
run the container in the background in a "detached" mode or in the
@ -65,7 +75,7 @@ default foreground mode::
Detached (-d)
.............
In detached mode (``-d=true`` or just ``-d``), all IO should be done
In detached mode (``-d=true`` or just ``-d``), all I/O should be done
through network connections or shared volumes because the container is
no longer listening to the commandline where you executed ``docker
run``. You can reattach to a detached container with ``docker``
@ -82,22 +92,68 @@ error. It can even pretend to be a TTY (this is what most commandline
executables expect) and pass along signals. All of that is
configurable::
-a=[] : Attach to stdin, stdout and/or stderr
-a=[] : Attach to ``stdin``, ``stdout`` and/or ``stderr``
-t=false : Allocate a pseudo-tty
-sig-proxy=true: Proxify all received signal to the process (even in non-tty mode)
-i=false : Keep stdin open even if not attached
-i=false : Keep STDIN open even if not attached
If you do not specify ``-a`` then Docker will `attach everything
(stdin,stdout,stderr)
<https://github.com/dotcloud/docker/blob/master/commands.go#L1797>`_. You
can specify which of the three standard streams (stdin, stdout,
stderr) you'd like to connect between your instead, as in::
<https://github.com/dotcloud/docker/blob/75a7f4d90cde0295bcfb7213004abce8d4779b75/commands.go#L1797>`_. 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 will typically want a tty
as well as persistent standard in, so you'll use ``-i -t`` together in
most interactive cases.
as well as persistent standard input (``stdin``), so you'll use ``-i
-t`` together in most interactive cases.
Container Identification
------------------------
Name (-name)
............
The operator can identify a container in three ways:
* UUID long identifier ("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778")
* UUID short identifier ("f78375b1c487")
* Name ("evil_ptolemy")
The UUID identifiers come from the Docker daemon, and if you do not
assign a name to the container with ``-name`` then the daemon will
also generate a random string name too. The name can become a handy
way to add meaning to a container since you can use this name when
defining :ref:`links <working_with_links_names>` (or any other place
you need to identify a container). This works for both background and
foreground Docker containers.
PID Equivalent
..............
And finally, to help with automation, you can have Docker write the
container ID out to a file of your choosing. This is similar to how
some programs might write out their process ID to a file (you've seen
them as PID files)::
-cidfile="": Write the container ID to the file
Network Settings
----------------
::
-n=true : Enable networking for this container
-dns=[] : Set custom dns servers for the container
By default, all containers have networking enabled and they can make
any outgoing connections. The operator can completely disable
networking with ``docker run -n`` which disables all incoming and outgoing
networking. In cases like this, you would perform I/O through files or
STDIN/STDOUT only.
Your container will use the same DNS servers as the host by default,
but you can override this with ``-dns``.
Clean Up (-rm)
--------------
@ -112,57 +168,84 @@ the container exits**, you can add the ``-rm`` flag::
-rm=false: Automatically remove the container when it exits (incompatible with -d)
Name (-name)
============
The operator can identify a container in three ways:
Runtime Constraints on CPU and Memory
-------------------------------------
* UUID long identifier ("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778")
* UUID short identifier ("f78375b1c487")
* name ("evil_ptolemy")
The operator can also adjust the performance parameters of the container::
The UUID identifiers come from the Docker daemon, and if you do not
assign a name to the container with ``-name`` then the daemon will
also generate a random string name too. The name can become a handy
way to add meaning to a container since you can use this name when
defining :ref:`links <working_with_links_names>` (or any other place
you need to identify a container). This works for both background and
foreground Docker containers.
-m="": Memory limit (format: <number><optional unit>, where unit = b, k, m or g)
-c=0 : CPU shares (relative weight)
PID Equivalent
==============
The operator can constrain the memory available to a container easily
with ``docker run -m``. If the host supports swap memory, then the
``-m`` memory setting can be larger than physical RAM.
And finally, to help with automation, you can have Docker write the
container id out to a file of your choosing. This is similar to how
some programs might write out their process ID to a file (you've seen
them as .pid files)::
Similarly the operator can increase the priority of this container
with the ``-c`` option. By default, all containers run at the same
priority and get the same proportion of CPU cycles, but you can tell
the kernel to give more shares of CPU time to one or more containers
when you start them via Docker.
-cidfile="": Write the container ID to the file
Runtime Privilege and LXC Configuration
---------------------------------------
Overriding Dockerfile Image Defaults
====================================
::
-privileged=false: Give extended privileges to this container
-lxc-conf=[]: Add custom lxc options -lxc-conf="lxc.cgroup.cpuset.cpus = 0,1"
By default, Docker containers are "unprivileged" and cannot, for
example, run a Docker daemon inside a Docker container. This is
because by default a container is not allowed to access any devices,
but a "privileged" container is given access to all devices (see
lxc-template.go_ and documentation on `cgroups devices
<https://www.kernel.org/doc/Documentation/cgroups/devices.txt>`_).
When the operator executes ``docker run -privileged``, Docker will
enable to access to all devices on the host as well as set some
configuration in AppArmor to allow the container nearly all the same
access to the host as processes running outside containers on the
host. Additional information about running with ``-privileged`` is
available on the `Docker Blog
<http://blog.docker.io/2013/09/docker-can-now-run-within-docker/>`_.
An operator can also specify LXC options using one or more
``-lxc-conf`` parameters. These can be new parameters or override
existing parameters from the lxc-template.go_. Note that in the
future, a given host's Docker daemon may not use LXC, so this is an
implementation-specific configuration meant for operators already
familiar with using LXC directly.
.. _lxc-template.go: https://github.com/dotcloud/docker/blob/master/execdriver/lxc/lxc_template.go
Overriding ``Dockerfile`` Image Defaults
========================================
When a developer builds an image from a :ref:`Dockerfile
<dockerbuilder>` or when she commits it, the developer can set a
number of default parameters that take effect when the image starts up
as a container.
Four of the Dockerfile commands cannot be overridden at runtime:
Four of the ``Dockerfile`` commands cannot be overridden at runtime:
``FROM, MAINTAINER, RUN``, and ``ADD``. Everything else has a
corresponding override in ``docker run``. We'll go through what the
developer might have set in each Dockerfile instruction and how the
developer might have set in each ``Dockerfile`` instruction and how the
operator can override that setting.
.. contents::
:local:
CMD
...
CMD (Default Command or Options)
--------------------------------
Remember the optional ``COMMAND`` in the Docker commandline::
Recall the optional ``COMMAND`` in the Docker commandline::
docker run [OPTIONS] IMAGE[:TAG] [COMMAND] [ARG...]
This command is optional because the person who created the ``IMAGE``
may have already provided a default ``COMMAND`` using the Dockerfile
may have already provided a default ``COMMAND`` using the ``Dockerfile``
``CMD``. As the operator (the person running a container from the
image), you can override that ``CMD`` just by specifying a new
``COMMAND``.
@ -171,22 +254,22 @@ If the image also specifies an ``ENTRYPOINT`` then the ``CMD`` or
``COMMAND`` get appended as arguments to the ``ENTRYPOINT``.
ENTRYPOINT
..........
ENTRYPOINT (Default Command to Execute at Runtime
-------------------------------------------------
::
-entrypoint="": Overwrite the default entrypoint set by the image
The ENTRYPOINT of an image is similar to a COMMAND because it
The ENTRYPOINT of an image is similar to a ``COMMAND`` because it
specifies what executable to run when the container starts, but it is
(purposely) more difficult to override. The ENTRYPOINT gives a
(purposely) more difficult to override. The ``ENTRYPOINT`` gives a
container its default nature or behavior, so that when you set an
ENTRYPOINT you can run the container *as if it were that binary*,
``ENTRYPOINT`` you can run the container *as if it were that binary*,
complete with default options, and you can pass in more options via
the COMMAND. But, sometimes an operator may want to run something else
inside the container, so you can override the default ENTRYPOINT at
runtime by using a string to specify the new ENTRYPOINT. Here is an
the ``COMMAND``. But, sometimes an operator may want to run something else
inside the container, so you can override the default ``ENTRYPOINT`` at
runtime by using a string to specify the new ``ENTRYPOINT``. Here is an
example of how to run a shell in a container that has been set up to
automatically run something else (like ``/usr/bin/redis-server``)::
@ -198,16 +281,14 @@ or two examples of how to pass more parameters to that ENTRYPOINT::
docker run -i -t -entrypoint /usr/bin/redis-cli example/redis --help
EXPOSE (``run`` Networking Options)
...................................
EXPOSE (Incoming Ports)
-----------------------
The *Dockerfile* doesn't give much control over networking, only
providing the EXPOSE instruction to give a hint to the operator about
what incoming ports might provide services. At runtime, however,
Docker provides a number of ``run`` options related to networking::
The ``Dockerfile`` doesn't give much control over networking, only
providing the ``EXPOSE`` instruction to give a hint to the operator
about what incoming ports might provide services. The following
options work with or override the ``Dockerfile``'s exposed defaults::
-n=true : Enable networking for this container
-dns=[] : Set custom dns servers for the container
-expose=[]: Expose a port from the container
without publishing it to your host
-P=false : Publish all exposed ports to the host interfaces
@ -217,25 +298,16 @@ Docker provides a number of ``run`` options related to networking::
(use 'docker port' to see the actual mapping)
-link="" : Add link to another container (name:alias)
By default, all containers have networking enabled and they can make
any outgoing connections. The operator can completely disable
networking with ``run -n`` which disables all incoming and outgoing
networking. In cases like this, you would perform IO through files or
stdin/stdout only.
Your container will use the same DNS servers as the host by default,
but you can override this with ``-dns``.
As mentioned previously, ``EXPOSE`` (and ``-expose``) make a port
available **in** a container for incoming connections. The port number
on the inside of the container (where the service listens) does not
need to be the same number as the port exposed on the outside of the
container (where clients connect), so inside the container you might
have an HTTP service listening on port 80 (and so you ``EXPOSE 80`` in
the Dockerfile), but outside the container the port might be 42800.
the ``Dockerfile``), but outside the container the port might be 42800.
To help a new client container reach the server container's internal
port operator ``-expose'd`` by the operator or ``EXPOSE'd`` by the
port operator ``-expose``'d by the operator or ``EXPOSE``'d by the
developer, the operator has three choices: start the server container
with ``-P`` or ``-p,`` or start the client container with ``-link``.
@ -250,10 +322,10 @@ networking interface. Docker will set some environment variables in
the client container to help indicate which interface and port to use.
ENV (Environment Variables)
...........................
---------------------------
The operator can **set any environment variable** in the container by
using one or more ``-e``, even overriding those already defined by the
using one or more ``-e`` flags, even overriding those already defined by the
developer with a Dockefile ``ENV``::
$ docker run -e "deep=purple" -rm ubuntu /bin/bash -c export
@ -287,7 +359,9 @@ container. Let's imagine we have a container running Redis::
2014/01/25 00:55:38 Error: No public port '6379' published for 4241164edf6f
Yet we can get information about the redis container's exposed ports with ``-link``. Choose an alias that will form a valid environment variable!
Yet we can get information about the Redis container's exposed ports
with ``-link``. Choose an alias that will form a valid environment
variable!
::
@ -312,7 +386,7 @@ And we can use that information to connect from another container as a client::
172.17.0.32:6379>
VOLUME (Shared Filesystems)
...........................
---------------------------
::
@ -322,32 +396,24 @@ VOLUME (Shared Filesystems)
The volumes commands are complex enough to have their own
documentation in section :ref:`volume_def`. A developer can define one
or more VOLUMEs associated with an image, but only the operator can
or more ``VOLUME``\s associated with an image, but only the operator can
give access from one container to another (or from a container to a
volume mounted on the host).
USER
....
----
::
The default user within a container is ``root`` (id = 0), but if the
developer created additional users, those are accessible too. The
developer can set a default user to run the first process with the
``Dockerfile USER`` command, but the operator can override it ::
-u="": Username or UID
WORKDIR
.......
-------
::
The default working directory for running binaries within a container is the root directory (``/``), but the developer can set a different default with the ``Dockerfile WORKDIR`` command. The operator can override this with::
-w="": Working directory inside the container
Performance
===========
The operator can also adjust the performance parameters of the container::
-c=0 : CPU shares (relative weight)
-m="": Memory limit (format: <number><optional unit>, where unit = b, k, m or g)
-lxc-conf=[]: Add custom lxc options -lxc-conf="lxc.cgroup.cpuset.cpus = 0,1"
-privileged=false: Give extended privileges to this container