DOCKER(1)

NAME
docker-run - Run a process in an isolated container

SYNOPSIS
docker run [-a|--attach[=]] [-c|--cpu-shares[=0] [-m|--memory=memory-limit] [--cidfile=file] [-d|--detach[=false]] [--dns=IP-address] [--name=name] [-u|--user=username|uid] [--link=name:alias] [-e|--env=environment] [--entrypoint=command] [--expose=port] [-P|--publish-all[=false]] [-p|--publish=port-mappping] [-h|--hostname=hostname] [--rm[=false]] [--priviledged[=false] [-i|--interactive[=false] [-t|--tty[=false]] [--lxc-conf=options] [-n|--networking[=true]] [-v|--volume=volume] [--volumes-from=container-id] [-w|--workdir=directory] [--sig-proxy[=true]] IMAGE [COMMAND] [ARG...]

DESCRIPTION

Run a process in a new container. docker run starts a process with its own file system, its own networking, and its own isolated process tree. The IMAGE which starts the process may define defaults related to the process that will be run in the container, the networking to expose, and more, but docker run gives final control to the operator or administrator who starts the container from the image. For that reason docker run has more options than any other docker command. If the IMAGE is not already loaded then docker run will pull the IMAGE, and all image dependencies, from the repository in the same way running docker pull IMAGE, before it starts the container from that image.

OPTIONS

-a, --attach=stdin|stdout|stderr:
    Attach to stdin, stdout or stderr. 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 commandline executables expect) and pass along signals. The -a option can be set for each of stdin, stdout, and stderr.

-c, --cpu-shares=0:
    CPU shares in relative weight. You can increase the priority of a 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 run.

-m, --memory=memory-limit:
    Allows you to constrain the memory available to a container. If the host supports swap memory, then the -m memory setting can be larger than physical RAM. If a limit of 0 is specified, the container's memory is not limited. The memory limit format: <number><optional unit>, where unit = b, k, m or g.

--cidfile=file:
    Write the container ID to the file specified.

-d, --detach=true|false:
    Detached mode. This runs the container in the background. It outputs the new container's id and and error messages. At any time you can run docker ps in the other shell to view a list of the running containers. You can reattach to a detached container with docker attach. If you choose to run a container in the detached mode, then you cannot use the -rm option.

--dns=IP-address:
    Set custom DNS servers. This option can be used to override the DNS configuration passed to the container. Typically this is necessary when the host DNS configuration is invalid for the container (eg. 127.0.0.1). When this is the case the -dns flags is necessary for every run.

-e, --env=environment:
    Set environment variables. This option allows you to specify arbitrary environment variables that are available for the process that will be launched inside of the container.

--entrypoint=command:
    This option allows you to overwrite the default entrypoint of the image that is set in the Dockerfile. 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 container its default nature or behavior, so that when you set an 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 --entrypoint and a string to specify the new ENTRYPOINT.

--expose=port:
    Expose a port from the container without publishing it to your host. A containers port can be exposed to other containers in three ways: 1) The developer can expose the port using the EXPOSE parameter of the Dockerfile, 2) the operator can use the --expose option with docker run, or 3) the container can be started with the --link.

-P, --publish-all=true|false:
    When set to true publish all exposed ports to the host interfaces. The default is false. If the operator uses -P (or -p) then Docker will make the exposed port accessible on the host and the ports will be available to any client that can reach the host. To find the map between the host ports and the exposed ports, use docker port.

-p, --publish=[]:
    Publish a container's port to the host (format: ip:hostPort:containerPort | ip::containerPort | hostPort:containerPort) (use 'docker port' to see the actual mapping)

-h , --hostname=hostname:
    Sets the container host name that is available inside the container.

-i , --interactive=true|false:
    When set to true, keep stdin open even if not attached. The default is false.

--link=name:alias:
    Add link to another container. The format is name:alias. If the operator uses --link when starting the new client container, then the client container can access the exposed port via a private networking interface. Docker will set some environment variables in the client container to help indicate which interface and port to use.

-n, --networking=true|false:
    By default, all containers have networking enabled (true) and can make outgoing connections. The operator can disable networking with --networking to false. This disables all incoming and outgoing networking. In cases like this, I/O can only be performed through files or by using STDIN/STDOUT. Also by default, the container will use the same DNS servers as the host. but you canThe operator may override this with -dns.

--name=name:
    Assign a name to the container. The operator can identify a container in three ways:

    UUID long identifier (“f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778”)
    UUID short identifier (“f78375b1c487”)
    Name (“jonah”)

    The UUID identifiers come from the Docker daemon, and if a name is not assigned to the container with --name then the daemon will also generate a random string name. The name is useful when defining links (see --link) (or any other place you need to identify a container). This works for both background and foreground Docker containers.

--privileged=true|false:
    Give extended privileges to this container. By default, Docker containers are “unprivileged” (=false) and cannot, for example, run a Docker daemon inside the Docker container. This is because by default a container is not allowed to access any devices. A “privileged” container is given access to all devices. When the operator executes docker run -privileged, Docker will enable 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 of a container on the host.

--rm=true|false:
    If set to true the container is automatically removed when it exits. The default is false. This option is incompatible with -d.

--sig-proxy=true|false:
    When set to true, proxify all received signals to the process (even in non-tty mode). The default is true.

-t, --tty=true|false:
    When set to true Docker can allocate a pseudo-tty and attach to the standard input of any container. This can be used, for example, to run a throwaway interactive shell. The default is value is false.

-u, --user=username,uid:
    Set a username or UID for the container.

-v, --volume=volume:
    Bind mount a volume to the container. The -v option can be used one or more times to add one or more mounts to a container. These mounts can then be used in other containers using the --volumes-from option. See examples.

--volumes-from=container-id:
    Will mount volumes from the specified container identified by container-id. Once a volume is mounted in a one container it can be shared with other containers using the --volumes-from option when running those other containers. The volumes can be shared even if the original container with the mount is not running.

-w, --workdir=directory:
    Working directory inside the container. The default working directory for running binaries within a container is the root directory (/). The developer can set a different default with the Dockerfile WORKDIR instruction. The operator can override the working directory by using the -w option.

IMAGE:
    The image name or ID.

COMMAND:
    The command or program to run inside the image.

ARG:
    The arguments for the command to be run in the container.

EXAMPLES

Exposing log messages from the container to the host's log

If you want messages that are logged in your container to show up in the host's syslog/journal then you should bind mount the /var/log directory as follows.

    docker run -v /dev/log:/dev/log -i -t fedora /bin/bash

From inside the container you can test this by sending a message to the log.

    logger "Hello from my container"

Then exit and check the journal.

    exit

    journalctl -b | grep hello

This should list the message sent to logger.

Attaching to one or more from STDIN, STDOUT, STDERR

If you do not specify -a then Docker will attach everything (stdin,stdout,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 fedora /bin/bash

Linking Containers

The link feature allows multiple containers to communicate with each other. For example, a container whose Dockerfile has exposed port 80 can be run and named as follows:

    docker run --name=link-test -d -i -t fedora/httpd

A second container, in this case called linker, can communicate with the httpd container, named link-test, by running with the --link=<name>:<alias>

    docker run -t -i --link=link-test:lt --name=linker fedora /bin/bash

Now the container linker is linked to container link-test with the alias lt. Running the env command in the linker container shows environment variables with the LT (alias) context (LT_)

    # env
    HOSTNAME=668231cb0978
    TERM=xterm
    LT_PORT_80_TCP=tcp://172.17.0.3:80
    LT_PORT_80_TCP_PORT=80
    LT_PORT_80_TCP_PROTO=tcp
    LT_PORT=tcp://172.17.0.3:80
    PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
    PWD=/
    LT_NAME=/linker/lt
    SHLVL=1
    HOME=/
    LT_PORT_80_TCP_ADDR=172.17.0.3
    _=/usr/bin/env

When linking two containers Docker will use the exposed ports of the container to create a secure tunnel for the parent to access.

Mapping Ports for External Usage

The exposed port of an application can be mapped to a host port using the -p flag. For example a httpd port 80 can be mapped to the host port 8080 using the following:

    docker run -p 8080:80 -d -i -t fedora/httpd

Creating and Mounting a Data Volume Container

Many applications require the sharing of persistent data across several containers. Docker allows you to create a Data Volume Container that other containers can mount from. For example, create a named container that contains directories /var/volume1 and /tmp/volume2. The image will need to contain these directories so a couple of RUN mkdir instructions might be required for you fedora-data image:

    docker run --name=data -v /var/volume1 -v /tmp/volume2 -i -t fedora-data true

    docker run --volumes-from=data --name=fedora-container1 -i -t fedora bash

Multiple --volumes-from parameters will bring together multiple data volumes from multiple containers. And it's possible to mount the volumes that came from the DATA container in yet another container via the fedora-container1 intermidiery container, allowing to abstract the actual data source from users of that data:

    docker run --volumes-from=fedora-container1 --name=fedora-container2 -i -t fedora bash

Mounting External Volumes

To mount a host directory as a container volume, specify the absolute path to the directory and the absolute path for the container directory separated by a colon:

    docker run -v /var/db:/data1 -i -t fedora bash

When using SELinux, be aware that the host has no knowledge of container SELinux policy. Therefore, in the above example, if SELinux policy is enforced, the /var/db directory is not writable to the container. A "Permission Denied" message will occur and an avc: message in the host's syslog.

To work around this, at time of writing this man page, the following command needs to be run in order for the proper SELinux policy type label to be attached to the host directory:

    chcon -Rt svirt_sandbox_file_t /var/db

Now, writing to the /data1 volume in the container will be allowed and the changes will also be reflected on the host in /var/db.

HISTORY
March 2014, Originally compiled by William Henry (whenry at redhat dot com) based on dockier.io source material and internal work.