23feaaa240
We want to be able to use container without the PID namespace. We basically want containers that can manage the host os, which I call Super Privileged Containers. We eventually would like to get to the point where the only namespace we use is the MNT namespace to bring the Apps userspace with it. By eliminating the PID namespace we can get better communication between the host and the clients and potentially tools like strace and gdb become easier to use. We also see tools like libvirtd running within a container telling systemd to place a VM in a particular cgroup, we need to have communications of the PID. I don't see us needing to share PID namespaces between containers, since this is really what docker exec does. So currently I see us just needing docker run --pid=host Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
680 lines
30 KiB
Markdown
680 lines
30 KiB
Markdown
page_title: Docker run reference
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page_description: Configure containers at runtime
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page_keywords: docker, run, configure, runtime
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# Docker run reference
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**Docker runs processes in isolated containers**. When an operator
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executes `docker run`, she starts a process with its own file system,
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its own networking, and its own isolated process tree. The
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[*Image*](/terms/image/#image) which starts the process may define
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defaults related to the binary to run, the networking to expose, and
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more, but `docker run` gives final control to the operator who starts
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the container from the image. That's the main reason
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[*run*](/reference/commandline/cli/#run) has more options than any
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other `docker` command.
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## General form
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The basic `docker run` command takes this form:
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$ sudo docker run [OPTIONS] IMAGE[:TAG] [COMMAND] [ARG...]
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To learn how to interpret the types of `[OPTIONS]`,
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see [*Option types*](/reference/commandline/cli/#option-types).
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The list of `[OPTIONS]` breaks down into two groups:
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1. Settings exclusive to operators, including:
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* Detached or Foreground running,
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* Container Identification,
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* Network settings, and
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* Runtime Constraints on CPU and Memory
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* Privileges and LXC Configuration
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2. Settings shared between operators and developers, where operators can
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override defaults developers set in images at build time.
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Together, the `docker run [OPTIONS]` give the operator complete control over runtime
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behavior, allowing them to override all defaults set by
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the developer during `docker build` and nearly all the defaults set by
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the Docker runtime itself.
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## Operator exclusive options
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Only the operator (the person executing `docker run`) can set the
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following options.
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- [Detached vs Foreground](#detached-vs-foreground)
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- [Detached (-d)](#detached-d)
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- [Foreground](#foreground)
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- [Container Identification](#container-identification)
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- [Name (--name)](#name-name)
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- [PID Equivalent](#pid-equivalent)
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- [IPC Settings](#ipc-settings)
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- [Network Settings](#network-settings)
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- [Clean Up (--rm)](#clean-up-rm)
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- [Runtime Constraints on CPU and Memory](#runtime-constraints-on-cpu-and-memory)
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- [Runtime Privilege, Linux Capabilities, and LXC Configuration](#runtime-privilege-linux-capabilities-and-lxc-configuration)
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## Detached vs foreground
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When starting a Docker container, you must first decide if you want to
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run the container in the background in a "detached" mode or in the
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default foreground mode:
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-d=false: Detached mode: Run container in the background, print new container id
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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/cli/#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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### Foreground
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In foreground mode (the default when `-d` is not specified), `docker
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run` can start the process in the container and attach the console to
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the process's standard input, output, and standard error. It can even
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pretend to be a TTY (this is what most command line executables expect)
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and pass along signals. All of that is configurable:
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-a=[] : Attach to `STDIN`, `STDOUT` and/or `STDERR`
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-t=false : Allocate a pseudo-tty
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--sig-proxy=true: Proxify all received signal to the process (non-TTY mode only)
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-i=false : Keep STDIN open even if not attached
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If you do not specify `-a` then Docker will [attach all standard
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streams]( https://github.com/docker/docker/blob/
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75a7f4d90cde0295bcfb7213004abce8d4779b75/commands.go#L1797). You can
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specify to which of the three standard streams (`STDIN`, `STDOUT`,
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`STDERR`) you'd like to connect instead, as in:
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$ sudo docker run -a stdin -a stdout -i -t ubuntu /bin/bash
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For interactive processes (like a shell), you must use `-i -t` together in
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order to allocate a tty for the container process. Specifying `-t` is however
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forbidden when the client standard output is redirected or pipe, such as in:
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`echo test | docker run -i busybox cat`.
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## Container identification
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### Name (--name)
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The operator can identify a container in three ways:
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- UUID long identifier
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("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778")
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- UUID short identifier ("f78375b1c487")
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- Name ("evil_ptolemy")
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The UUID identifiers come from the Docker daemon, and if you do not
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assign a name to the container with `--name` then the daemon will also
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generate a random string name too. The name can become a handy way to
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add meaning to a container since you can use this name when defining
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[*links*](/userguide/dockerlinks) (or any
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other place you need to identify a container). This works for both
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background and foreground Docker containers.
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### PID equivalent
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Finally, to help with automation, you can have Docker write the
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container ID out to a file of your choosing. This is similar to how some
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programs might write out their process ID to a file (you've seen them as
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PID files):
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--cidfile="": Write the container ID to the file
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### Image[:tag]
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While not strictly a means of identifying a container, you can specify a version of an
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image you'd like to run the container with by adding `image[:tag]` to the command. For
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example, `docker run ubuntu:14.04`.
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## PID Settings
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--pid="" : Set the PID (Process) Namespace mode for the container,
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'host': use the host's PID namespace inside the container
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By default, all containers have the PID namespace enabled.
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PID namespace provides separation of processes. The PID Namespace removes the
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view of the system processes, and allows process ids to be reused including
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pid 1.
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In certain cases you want your container to share the host's process namespace,
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basically allowing processes within the container to see all of the processes
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on the system. For example, you could build a container with debugging tools
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like `strace` or `gdb`, but want to use these tools when debugging processes
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within the container.
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$ sudo docker run --pid=host rhel7 strace -p 1234
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This command would allow you to use `strace` inside the container on pid 1234 on
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the host.
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## IPC Settings
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--ipc="" : Set the IPC mode for the container,
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'container:<name|id>': reuses another container's IPC namespace
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'host': use the host's IPC namespace inside the container
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By default, all containers have the IPC namespace enabled.
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IPC (POSIX/SysV IPC) namespace provides separation of named shared memory segments, semaphores and message queues.
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Shared memory segments are used to accelerate inter-process communication at
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memory speed, rather than through pipes or through the network stack. Shared
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memory is commonly used by databases and custom-built (typically C/OpenMPI,
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C++/using boost libraries) high performance applications for scientific
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computing and financial services industries. If these types of applications
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are broken into multiple containers, you might need to share the IPC mechanisms
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of the containers.
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## Network settings
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--dns=[] : Set custom dns servers for the container
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--net="bridge" : Set the Network mode for the container
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'bridge': creates a new network stack for the container on the docker bridge
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'none': no networking for this container
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'container:<name|id>': reuses another container network stack
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'host': use the host network stack inside the container
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--add-host="" : Add a line to /etc/hosts (host:IP)
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--mac-address="" : Sets the container's Ethernet device's MAC address
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By default, all containers have networking enabled and they can make any
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outgoing connections. The operator can completely disable networking
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with `docker run --net none` which disables all incoming and outgoing
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networking. In cases like this, you would perform I/O through files or
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`STDIN` and `STDOUT` only.
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Your container will use the same DNS servers as the host by default, but
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you can override this with `--dns`.
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By default a random MAC is generated. You can set the container's MAC address
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explicitly by providing a MAC via the `--mac-address` parameter (format:
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`12:34:56:78:9a:bc`).
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Supported networking modes are:
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* none - no networking in the container
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* bridge - (default) connect the container to the bridge via veth interfaces
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* host - use the host's network stack inside the container. Note: This gives the container full access to local system services such as D-bus and is therefore considered insecure.
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* container - use another container's network stack
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#### Mode: none
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With the networking mode set to `none` a container will not have a
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access to any external routes. The container will still have a
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`loopback` interface enabled in the container but it does not have any
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routes to external traffic.
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#### Mode: bridge
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With the networking mode set to `bridge` a container will use docker's
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default networking setup. A bridge is setup on the host, commonly named
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`docker0`, and a pair of `veth` interfaces will be created for the
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container. One side of the `veth` pair will remain on the host attached
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to the bridge while the other side of the pair will be placed inside the
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container's namespaces in addition to the `loopback` interface. An IP
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address will be allocated for containers on the bridge's network and
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traffic will be routed though this bridge to the container.
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#### Mode: host
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With the networking mode set to `host` a container will share the host's
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network stack and all interfaces from the host will be available to the
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container. The container's hostname will match the hostname on the host
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system. Publishing ports and linking to other containers will not work
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when sharing the host's network stack.
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#### Mode: container
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With the networking mode set to `container` a container will share the
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network stack of another container. The other container's name must be
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provided in the format of `--net container:<name|id>`.
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Example running a Redis container with Redis binding to `localhost` then
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running the `redis-cli` command and connecting to the Redis server over the
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`localhost` interface.
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$ sudo docker run -d --name redis example/redis --bind 127.0.0.1
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$ # use the redis container's network stack to access localhost
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$ sudo docker run --rm -ti --net container:redis example/redis-cli -h 127.0.0.1
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### Managing /etc/hosts
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Your container will have lines in `/etc/hosts` which define the hostname of the
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container itself as well as `localhost` and a few other common things. The
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`--add-host` flag can be used to add additional lines to `/etc/hosts`.
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$ /docker run -ti --add-host db-static:86.75.30.9 ubuntu cat /etc/hosts
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172.17.0.22 09d03f76bf2c
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fe00::0 ip6-localnet
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ff00::0 ip6-mcastprefix
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ff02::1 ip6-allnodes
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ff02::2 ip6-allrouters
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127.0.0.1 localhost
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::1 localhost ip6-localhost ip6-loopback
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86.75.30.9 db-static
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## Clean up (--rm)
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By default a container's file system persists even after the container
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exits. This makes debugging a lot easier (since you can inspect the
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final state) and you retain all your data by default. But if you are
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running short-term **foreground** processes, these container file
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systems can really pile up. If instead you'd like Docker to
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**automatically clean up the container and remove the file system when
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the container exits**, you can add the `--rm` flag:
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--rm=false: Automatically remove the container when it exits (incompatible with -d)
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## Security configuration
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--security-opt="label:user:USER" : Set the label user for the container
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--security-opt="label:role:ROLE" : Set the label role for the container
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--security-opt="label:type:TYPE" : Set the label type for the container
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--security-opt="label:level:LEVEL" : Set the label level for the container
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--security-opt="label:disable" : Turn off label confinement for the container
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--security-opt="apparmor:PROFILE" : Set the apparmor profile to be applied
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to the container
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You can override the default labeling scheme for each container by specifying
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the `--security-opt` flag. For example, you can specify the MCS/MLS level, a
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requirement for MLS systems. Specifying the level in the following command
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allows you to share the same content between containers.
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# docker run --security-opt label:level:s0:c100,c200 -i -t fedora bash
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An MLS example might be:
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# docker run --security-opt label:level:TopSecret -i -t rhel7 bash
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To disable the security labeling for this container versus running with the
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`--permissive` flag, use the following command:
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# docker run --security-opt label:disable -i -t fedora bash
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If you want a tighter security policy on the processes within a container,
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you can specify an alternate type for the container. You could run a container
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that is only allowed to listen on Apache ports by executing the following
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command:
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# docker run --security-opt label:type:svirt_apache_t -i -t centos bash
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Note:
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You would have to write policy defining a `svirt_apache_t` type.
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## Runtime constraints on CPU and memory
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The operator can also adjust the performance parameters of the
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container:
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-m="": Memory limit (format: <number><optional unit>, where unit = b, k, m or g)
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-c=0 : CPU shares (relative weight)
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The operator can constrain the memory available to a container easily
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with `docker run -m`. If the host supports swap memory, then the `-m`
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memory setting can be larger than physical RAM.
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Similarly the operator can increase the priority of this container with
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the `-c` option. By default, all containers run at the same priority and
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get the same proportion of CPU cycles, but you can tell the kernel to
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give more shares of CPU time to one or more containers when you start
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them via Docker.
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The flag `-c` or `--cpu-shares` with value 0 indicates that the running
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container has access to all 1024 (default) CPU shares. However, this value
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can be modified to run a container with a different priority or different
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proportion of CPU cycles.
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E.g., If we start three {C0, C1, C2} containers with default values
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(`-c` OR `--cpu-shares` = 0) and one {C3} with (`-c` or `--cpu-shares`=512)
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then C0, C1, and C2 would have access to 100% CPU shares (1024) and C3 would
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only have access to 50% CPU shares (512). In the context of a time-sliced OS
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with time quantum set as 100 milliseconds, containers C0, C1, and C2 will run
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for full-time quantum, and container C3 will run for half-time quantum i.e 50
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milliseconds.
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## Runtime privilege, Linux capabilities, and LXC configuration
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--cap-add: Add Linux capabilities
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--cap-drop: Drop Linux capabilities
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--privileged=false: Give extended privileges to this container
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--device=[]: Allows you to run devices inside the container without the --privileged flag.
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--lxc-conf=[]: (lxc exec-driver only) Add custom lxc options --lxc-conf="lxc.cgroup.cpuset.cpus = 0,1"
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By default, Docker containers are "unprivileged" and cannot, for
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example, run a Docker daemon inside a Docker container. This is because
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by default a container is not allowed to access any devices, but a
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"privileged" container is given access to all devices (see [lxc-template.go](
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https://github.com/docker/docker/blob/master/daemon/execdriver/lxc/lxc_template.go)
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and documentation on [cgroups devices](
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https://www.kernel.org/doc/Documentation/cgroups/devices.txt)).
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When the operator executes `docker run --privileged`, Docker will enable
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to access to all devices on the host as well as set some configuration
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in AppArmor or SELinux to allow the container nearly all the same access to the
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host as processes running outside containers on the host. Additional
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information about running with `--privileged` is available on the
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[Docker Blog](http://blog.docker.com/2013/09/docker-can-now-run-within-docker/).
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If you want to limit access to a specific device or devices you can use
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the `--device` flag. It allows you to specify one or more devices that
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will be accessible within the container.
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$ sudo docker run --device=/dev/snd:/dev/snd ...
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By default, the container will be able to `read`, `write`, and `mknod` these devices.
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This can be overridden using a third `:rwm` set of options to each `--device` flag:
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```
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$ sudo docker run --device=/dev/sda:/dev/xvdc --rm -it ubuntu fdisk /dev/xvdc
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Command (m for help): q
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$ sudo docker run --device=/dev/sda:/dev/xvdc:r --rm -it ubuntu fdisk /dev/xvdc
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You will not be able to write the partition table.
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Command (m for help): q
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$ sudo docker run --device=/dev/sda:/dev/xvdc:w --rm -it ubuntu fdisk /dev/xvdc
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crash....
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$ sudo docker run --device=/dev/sda:/dev/xvdc:m --rm -it ubuntu fdisk /dev/xvdc
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fdisk: unable to open /dev/xvdc: Operation not permitted
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```
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||
In addition to `--privileged`, the operator can have fine grain control over the
|
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capabilities using `--cap-add` and `--cap-drop`. By default, Docker has a default
|
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list of capabilities that are kept. Both flags support the value `all`, so if the
|
||
operator wants to have all capabilities but `MKNOD` they could use:
|
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|
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$ sudo docker run --cap-add=ALL --cap-drop=MKNOD ...
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|
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For interacting with the network stack, instead of using `--privileged` they
|
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should use `--cap-add=NET_ADMIN` to modify the network interfaces.
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|
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$ docker run -t -i --rm ubuntu:14.04 ip link add dummy0 type dummy
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RTNETLINK answers: Operation not permitted
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$ docker run -t -i --rm --cap-add=NET_ADMIN ubuntu:14.04 ip link add dummy0 type dummy
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|
||
To mount a FUSE based filesystem, you need to combine both `--cap-add` and
|
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`--device`:
|
||
|
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$ docker run --rm -it --cap-add SYS_ADMIN sshfs sshfs sven@10.10.10.20:/home/sven /mnt
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fuse: failed to open /dev/fuse: Operation not permitted
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$ docker run --rm -it --device /dev/fuse sshfs sshfs sven@10.10.10.20:/home/sven /mnt
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fusermount: mount failed: Operation not permitted
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$ docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse sshfs
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# sshfs sven@10.10.10.20:/home/sven /mnt
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The authenticity of host '10.10.10.20 (10.10.10.20)' can't be established.
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ECDSA key fingerprint is 25:34:85:75:25:b0:17:46:05:19:04:93:b5:dd:5f:c6.
|
||
Are you sure you want to continue connecting (yes/no)? yes
|
||
sven@10.10.10.20's password:
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root@30aa0cfaf1b5:/# ls -la /mnt/src/docker
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total 1516
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drwxrwxr-x 1 1000 1000 4096 Dec 4 06:08 .
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drwxrwxr-x 1 1000 1000 4096 Dec 4 11:46 ..
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-rw-rw-r-- 1 1000 1000 16 Oct 8 00:09 .dockerignore
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-rwxrwxr-x 1 1000 1000 464 Oct 8 00:09 .drone.yml
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||
drwxrwxr-x 1 1000 1000 4096 Dec 4 06:11 .git
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-rw-rw-r-- 1 1000 1000 461 Dec 4 06:08 .gitignore
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....
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||
|
||
|
||
If the Docker daemon was started using the `lxc` exec-driver
|
||
(`docker -d --exec-driver=lxc`) then the 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](
|
||
https://github.com/docker/docker/blob/master/daemon/execdriver/lxc/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.
|
||
|
||
> **Note:**
|
||
> If you use `--lxc-conf` to modify a container's configuration which is also
|
||
> managed by the Docker daemon, then the Docker daemon will not know about this
|
||
> modification, and you will need to manage any conflicts yourself. For example,
|
||
> you can use `--lxc-conf` to set a container's IP address, but this will not be
|
||
> reflected in the `/etc/hosts` file.
|
||
|
||
## Overriding Dockerfile image defaults
|
||
|
||
When a developer builds an image from a [*Dockerfile*](/reference/builder)
|
||
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: `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 operator can override that setting.
|
||
|
||
- [CMD (Default Command or Options)](#cmd-default-command-or-options)
|
||
- [ENTRYPOINT (Default Command to Execute at Runtime)](
|
||
#entrypoint-default-command-to-execute-at-runtime)
|
||
- [EXPOSE (Incoming Ports)](#expose-incoming-ports)
|
||
- [ENV (Environment Variables)](#env-environment-variables)
|
||
- [VOLUME (Shared Filesystems)](#volume-shared-filesystems)
|
||
- [USER](#user)
|
||
- [WORKDIR](#workdir)
|
||
|
||
## CMD (default command or options)
|
||
|
||
Recall the optional `COMMAND` in the Docker
|
||
commandline:
|
||
|
||
$ sudo 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 `CMD`
|
||
instruction. As the operator (the person running a container from the
|
||
image), you can override that `CMD` instruction just by specifying a new
|
||
`COMMAND`.
|
||
|
||
If the image also specifies an `ENTRYPOINT` then the `CMD` or `COMMAND`
|
||
get appended as arguments to the `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
|
||
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 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`):
|
||
|
||
$ sudo docker run -i -t --entrypoint /bin/bash example/redis
|
||
|
||
or two examples of how to pass more parameters to that ENTRYPOINT:
|
||
|
||
$ sudo docker run -i -t --entrypoint /bin/bash example/redis -c ls -l
|
||
$ sudo docker run -i -t --entrypoint /usr/bin/redis-cli example/redis --help
|
||
|
||
## 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. The following options work with
|
||
or override the Dockerfile's exposed defaults:
|
||
|
||
--expose=[]: Expose a port or a range of ports from the container
|
||
without publishing it to your host
|
||
-P=false : Publish all exposed ports to the host interfaces
|
||
-p=[] : Publish a container᾿s port or a range of ports to the host
|
||
format: ip:hostPort:containerPort | ip::containerPort | hostPort:containerPort | containerPort
|
||
Both hostPort and containerPort can be specified as a range of ports.
|
||
When specifying ranges for both, the number of container ports in the range must match the number of host ports in the range. (e.g., `-p 1234-1236:1234-1236/tcp`)
|
||
(use 'docker port' to see the actual mapping)
|
||
--link="" : Add link to another container (name:alias)
|
||
|
||
As mentioned previously, `EXPOSE` (and `--expose`) makes ports 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.
|
||
|
||
To help a new client container reach the server container's internal
|
||
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`.
|
||
|
||
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. When using `-P`, Docker will bind the exposed
|
||
ports to a random port on the host between 49153 and 65535. To find the
|
||
mapping between the host ports and the exposed ports, use `docker port`.
|
||
|
||
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.
|
||
|
||
## ENV (environment variables)
|
||
|
||
When a new container is created, Docker will set the following environment
|
||
variables automatically:
|
||
|
||
<table width=100%>
|
||
<tr style="background-color:#C0C0C0">
|
||
<td> <b>Variable</b> </td>
|
||
<td style="padding-left:10px"> <b>Value</b> </td>
|
||
</tr>
|
||
<tr>
|
||
<td> <code>HOME</code> </td>
|
||
<td style="padding-left:10px">
|
||
Set based on the value of <code>USER</code>
|
||
</td>
|
||
</tr>
|
||
<tr style="background-color:#E8E8E8">
|
||
<td valign=top> <code>HOSTNAME</code> </td>
|
||
<td style="padding-left:10px">
|
||
The hostname associated with the container
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td valign=top> <code>PATH</code> </td>
|
||
<td style="padding-left:10px">
|
||
Includes popular directories, such as :<br>
|
||
<code>/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin</code>
|
||
</td>
|
||
<tr style="background-color:#E8E8E8">
|
||
<td valign=top> <code>TERM</code> </td>
|
||
<td style="padding-left:10px">
|
||
<code>xterm</code> if the container is allocated a psuedo-TTY
|
||
</td>
|
||
</tr>
|
||
</table>
|
||
|
||
The container may also include environment variables defined
|
||
as a result of the container being linked with another container. See
|
||
the [*Container Links*](/userguide/dockerlinks/#container-linking)
|
||
section for more details.
|
||
|
||
Additionally, the operator can **set any environment variable** in the
|
||
container by using one or more `-e` flags, even overriding those mentioned
|
||
above, or already defined by the developer with a Dockerfile `ENV`:
|
||
|
||
$ sudo docker run -e "deep=purple" --rm ubuntu /bin/bash -c export
|
||
declare -x HOME="/"
|
||
declare -x HOSTNAME="85bc26a0e200"
|
||
declare -x OLDPWD
|
||
declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
|
||
declare -x PWD="/"
|
||
declare -x SHLVL="1"
|
||
declare -x container="lxc"
|
||
declare -x deep="purple"
|
||
|
||
Similarly the operator can set the **hostname** with `-h`.
|
||
|
||
`--link name:alias` also sets environment variables, using the *alias* string to
|
||
define environment variables within the container that give the IP and PORT
|
||
information for connecting to the service container. Let's imagine we have a
|
||
container running Redis:
|
||
|
||
# Start the service container, named redis-name
|
||
$ sudo docker run -d --name redis-name dockerfiles/redis
|
||
4241164edf6f5aca5b0e9e4c9eccd899b0b8080c64c0cd26efe02166c73208f3
|
||
|
||
# The redis-name container exposed port 6379
|
||
$ sudo docker ps
|
||
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
|
||
4241164edf6f $ dockerfiles/redis:latest /redis-stable/src/re 5 seconds ago Up 4 seconds 6379/tcp redis-name
|
||
|
||
# Note that there are no public ports exposed since we didn᾿t use -p or -P
|
||
$ sudo docker port 4241164edf6f 6379
|
||
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!
|
||
|
||
$ sudo docker run --rm --link redis-name:redis_alias --entrypoint /bin/bash dockerfiles/redis -c export
|
||
declare -x HOME="/"
|
||
declare -x HOSTNAME="acda7f7b1cdc"
|
||
declare -x OLDPWD
|
||
declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
|
||
declare -x PWD="/"
|
||
declare -x REDIS_ALIAS_NAME="/distracted_wright/redis"
|
||
declare -x REDIS_ALIAS_PORT="tcp://172.17.0.32:6379"
|
||
declare -x REDIS_ALIAS_PORT_6379_TCP="tcp://172.17.0.32:6379"
|
||
declare -x REDIS_ALIAS_PORT_6379_TCP_ADDR="172.17.0.32"
|
||
declare -x REDIS_ALIAS_PORT_6379_TCP_PORT="6379"
|
||
declare -x REDIS_ALIAS_PORT_6379_TCP_PROTO="tcp"
|
||
declare -x SHLVL="1"
|
||
declare -x container="lxc"
|
||
|
||
And we can use that information to connect from another container as a client:
|
||
|
||
$ sudo docker run -i -t --rm --link redis-name:redis_alias --entrypoint /bin/bash dockerfiles/redis -c '/redis-stable/src/redis-cli -h $REDIS_ALIAS_PORT_6379_TCP_ADDR -p $REDIS_ALIAS_PORT_6379_TCP_PORT'
|
||
172.17.0.32:6379>
|
||
|
||
Docker will also map the private IP address to the alias of a linked
|
||
container by inserting an entry into `/etc/hosts`. You can use this
|
||
mechanism to communicate with a linked container by its alias:
|
||
|
||
$ sudo docker run -d --name servicename busybox sleep 30
|
||
$ sudo docker run -i -t --link servicename:servicealias busybox ping -c 1 servicealias
|
||
|
||
If you restart the source container (`servicename` in this case), the recipient
|
||
container's `/etc/hosts` entry will be automatically updated.
|
||
|
||
## VOLUME (shared filesystems)
|
||
|
||
-v=[]: Create a bind mount with: [host-dir]:[container-dir]:[rw|ro].
|
||
If "container-dir" is missing, then docker creates a new volume.
|
||
--volumes-from="": Mount all volumes from the given container(s)
|
||
|
||
The volumes commands are complex enough to have their own documentation
|
||
in section [*Managing data in
|
||
containers*](/userguide/dockervolumes). A developer can define
|
||
one 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` instruction, but the operator can override it:
|
||
|
||
-u="": Username or UID
|
||
|
||
> **Note:** if you pass numeric uid, it must be in range 0-2147483647.
|
||
|
||
## 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
|