14 KiB
% DOCKER(1) Docker User Manuals % William Henry % APRIL 2014
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.
--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 any 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.
-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. The memory limit format: , where unit = b, k, m or g.
-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. The 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.
(bash)# 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=:
# 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
April 2014, Originally compiled by William Henry (whenry at redhat dot com) based on docker.io source material and internal work.