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41de7a18d8
The purpose of this PR is for users to distinguish Docker errors from contained command errors. This PR modifies 'docker run' exit codes to follow the chroot standard for exit codes. Exit status: 125 if 'docker run' itself fails 126 if contained command cannot be invoked 127 if contained command cannot be found the exit status otherwise Signed-off-by: Sally O'Malley <somalley@redhat.com>
767 lines
30 KiB
Markdown
767 lines
30 KiB
Markdown
% DOCKER(1) Docker User Manuals
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% Docker Community
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% JUNE 2014
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# NAME
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docker-run - Run a command in a new container
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# SYNOPSIS
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**docker run**
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[**-a**|**--attach**[=*[]*]]
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[**--add-host**[=*[]*]]
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[**--blkio-weight**[=*[BLKIO-WEIGHT]*]]
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[**--cpu-shares**[=*0*]]
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[**--cap-add**[=*[]*]]
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[**--cap-drop**[=*[]*]]
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[**--cgroup-parent**[=*CGROUP-PATH*]]
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[**--cidfile**[=*CIDFILE*]]
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[**--cpu-period**[=*0*]]
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[**--cpu-quota**[=*0*]]
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[**--cpuset-cpus**[=*CPUSET-CPUS*]]
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[**--cpuset-mems**[=*CPUSET-MEMS*]]
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[**-d**|**--detach**[=*false*]]
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[**--device**[=*[]*]]
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[**--dns**[=*[]*]]
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[**--dns-opt**[=*[]*]]
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[**--dns-search**[=*[]*]]
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[**-e**|**--env**[=*[]*]]
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[**--entrypoint**[=*ENTRYPOINT*]]
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[**--env-file**[=*[]*]]
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[**--expose**[=*[]*]]
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[**--group-add**[=*[]*]]
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[**-h**|**--hostname**[=*HOSTNAME*]]
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[**--help**]
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[**-i**|**--interactive**[=*false*]]
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[**--ipc**[=*IPC*]]
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[**--kernel-memory**[=*KERNEL-MEMORY*]]
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[**-l**|**--label**[=*[]*]]
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[**--label-file**[=*[]*]]
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[**--link**[=*[]*]]
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[**--log-driver**[=*[]*]]
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[**--log-opt**[=*[]*]]
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[**--lxc-conf**[=*[]*]]
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[**-m**|**--memory**[=*MEMORY*]]
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[**--mac-address**[=*MAC-ADDRESS*]]
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[**--memory-reservation**[=*MEMORY-RESERVATION*]]
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[**--memory-swap**[=*MEMORY-SWAP*]]
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[**--memory-swappiness**[=*MEMORY-SWAPPINESS*]]
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[**--name**[=*NAME*]]
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[**--net**[=*"bridge"*]]
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[**--oom-kill-disable**[=*false*]]
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[**-P**|**--publish-all**[=*false*]]
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[**-p**|**--publish**[=*[]*]]
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[**--pid**[=*[]*]]
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[**--privileged**[=*false*]]
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[**--read-only**[=*false*]]
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[**--restart**[=*RESTART*]]
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[**--rm**[=*false*]]
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[**--security-opt**[=*[]*]]
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[**--stop-signal**[=*SIGNAL*]]
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[**--sig-proxy**[=*true*]]
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[**-t**|**--tty**[=*false*]]
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[**-u**|**--user**[=*USER*]]
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[**-v**|**--volume**[=*[]*]]
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[**--ulimit**[=*[]*]]
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[**--uts**[=*[]*]]
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[**--volumes-from**[=*[]*]]
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[**-w**|**--workdir**[=*WORKDIR*]]
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IMAGE [COMMAND] [ARG...]
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# DESCRIPTION
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Run a process in a new container. **docker run** starts a process with its own
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file system, its own networking, and its own isolated process tree. The IMAGE
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which starts the process may define defaults related to the process that will be
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run in the container, the networking to expose, and more, but **docker run**
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gives final control to the operator or administrator who starts the container
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from the image. For that reason **docker run** has more options than any other
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Docker command.
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If the IMAGE is not already loaded then **docker run** will pull the IMAGE, and
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all image dependencies, from the repository in the same way running **docker
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pull** IMAGE, before it starts the container from that image.
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# OPTIONS
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**-a**, **--attach**=[]
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Attach to STDIN, STDOUT or STDERR.
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In foreground mode (the default when **-d**
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is not specified), **docker run** can start the process in the container
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and attach the console to the process’s standard input, output, and standard
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error. It can even pretend to be a TTY (this is what most commandline
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executables expect) and pass along signals. The **-a** option can be set for
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each of stdin, stdout, and stderr.
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**--add-host**=[]
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Add a custom host-to-IP mapping (host:ip)
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Add a line to /etc/hosts. The format is hostname:ip. The **--add-host**
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option can be set multiple times.
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**--blkio-weight**=0
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Block IO weight (relative weight) accepts a weight value between 10 and 1000.
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**--cpu-shares**=0
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CPU shares (relative weight)
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By default, all containers get the same proportion of CPU cycles. This proportion
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can be modified by changing the container's CPU share weighting relative
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to the weighting of all other running containers.
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To modify the proportion from the default of 1024, use the **--cpu-shares**
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flag to set the weighting to 2 or higher.
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The proportion will only apply when CPU-intensive processes are running.
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When tasks in one container are idle, other containers can use the
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left-over CPU time. The actual amount of CPU time will vary depending on
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the number of containers running on the system.
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For example, consider three containers, one has a cpu-share of 1024 and
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two others have a cpu-share setting of 512. When processes in all three
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containers attempt to use 100% of CPU, the first container would receive
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50% of the total CPU time. If you add a fourth container with a cpu-share
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of 1024, the first container only gets 33% of the CPU. The remaining containers
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receive 16.5%, 16.5% and 33% of the CPU.
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On a multi-core system, the shares of CPU time are distributed over all CPU
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cores. Even if a container is limited to less than 100% of CPU time, it can
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use 100% of each individual CPU core.
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For example, consider a system with more than three cores. If you start one
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container **{C0}** with **-c=512** running one process, and another container
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**{C1}** with **-c=1024** running two processes, this can result in the following
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division of CPU shares:
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PID container CPU CPU share
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100 {C0} 0 100% of CPU0
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101 {C1} 1 100% of CPU1
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102 {C1} 2 100% of CPU2
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**--cap-add**=[]
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Add Linux capabilities
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**--cap-drop**=[]
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Drop Linux capabilities
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**--cgroup-parent**=""
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Path to cgroups under which the cgroup for the container will be created. If the path is not absolute, the path is considered to be relative to the cgroups path of the init process. Cgroups will be created if they do not already exist.
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**--cidfile**=""
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Write the container ID to the file
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**--cpu-period**=0
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Limit the CPU CFS (Completely Fair Scheduler) period
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Limit the container's CPU usage. This flag tell the kernel to restrict the container's CPU usage to the period you specify.
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**--cpuset-cpus**=""
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CPUs in which to allow execution (0-3, 0,1)
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**--cpuset-mems**=""
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Memory nodes (MEMs) in which to allow execution (0-3, 0,1). Only effective on NUMA systems.
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If you have four memory nodes on your system (0-3), use `--cpuset-mems=0,1`
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then processes in your Docker container will only use memory from the first
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two memory nodes.
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**--cpu-quota**=0
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Limit the CPU CFS (Completely Fair Scheduler) quota
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Limit the container's CPU usage. By default, containers run with the full
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CPU resource. This flag tell the kernel to restrict the container's CPU usage
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to the quota you specify.
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**-d**, **--detach**=*true*|*false*
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Detached mode: run the container in the background and print the new container ID. The default is *false*.
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At any time you can run **docker ps** in
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the other shell to view a list of the running containers. You can reattach to a
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detached container with **docker attach**. If you choose to run a container in
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the detached mode, then you cannot use the **-rm** option.
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When attached in the tty mode, you can detach from a running container without
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stopping the process by pressing the keys CTRL-P CTRL-Q.
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**--device**=[]
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Add a host device to the container (e.g. --device=/dev/sdc:/dev/xvdc:rwm)
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**--dns-search**=[]
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Set custom DNS search domains (Use --dns-search=. if you don't wish to set the search domain)
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**--dns-opt**=[]
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Set custom DNS options
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**--dns**=[]
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Set custom DNS servers
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This option can be used to override the DNS
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configuration passed to the container. Typically this is necessary when the
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host DNS configuration is invalid for the container (e.g., 127.0.0.1). When this
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is the case the **--dns** flags is necessary for every run.
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**-e**, **--env**=[]
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Set environment variables
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This option allows you to specify arbitrary
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environment variables that are available for the process that will be launched
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inside of the container.
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**--entrypoint**=""
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Overwrite the default ENTRYPOINT of the image
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This option allows you to overwrite the default entrypoint of the image that
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is set in the Dockerfile. The ENTRYPOINT of an image is similar to a COMMAND
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because it specifies what executable to run when the container starts, but it is
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(purposely) more difficult to override. The ENTRYPOINT gives a container its
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default nature or behavior, so that when you set an ENTRYPOINT you can run the
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container as if it were that binary, complete with default options, and you can
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pass in more options via the COMMAND. But, sometimes an operator may want to run
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something else inside the container, so you can override the default ENTRYPOINT
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at runtime by using a **--entrypoint** and a string to specify the new
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ENTRYPOINT.
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**--env-file**=[]
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Read in a line delimited file of environment variables
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**--expose**=[]
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Expose a port, or a range of ports (e.g. --expose=3300-3310) informs Docker
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that the container listens on the specified network ports at runtime. Docker
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uses this information to interconnect containers using links and to set up port
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redirection on the host system.
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**--group-add**=[]
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Add additional groups to run as
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**-h**, **--hostname**=""
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Container host name
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Sets the container host name that is available inside the container.
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**--help**
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Print usage statement
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**-i**, **--interactive**=*true*|*false*
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Keep STDIN open even if not attached. The default is *false*.
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When set to true, keep stdin open even if not attached. The default is false.
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**--ipc**=""
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Default is to create a private IPC namespace (POSIX SysV IPC) for the container
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'container:<name|id>': reuses another container shared memory, semaphores and message queues
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'host': use the host shared memory,semaphores and message queues inside the container. Note: the host mode gives the container full access to local shared memory and is therefore considered insecure.
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**-l**, **--label**=[]
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Set metadata on the container (e.g., --label com.example.key=value)
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**--kernel-memory**=""
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Kernel memory limit (format: `<number>[<unit>]`, where unit = b, k, m or g)
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Constrains the kernel memory available to a container. If a limit of 0
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is specified (not using `--kernel-memory`), the container's kernel memory
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is not limited. If you specify a limit, it may be rounded up to a multiple
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of the operating system's page size and the value can be very large,
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millions of trillions.
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**--label-file**=[]
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Read in a line delimited file of labels
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**--link**=[]
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Add link to another container in the form of <name or id>:alias or just <name or id>
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in which case the alias will match the name
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If the operator
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uses **--link** when starting the new client container, then the client
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container can access the exposed port via a private networking interface. Docker
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will set some environment variables in the client container to help indicate
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which interface and port to use.
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**--lxc-conf**=[]
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(lxc exec-driver only) Add custom lxc options --lxc-conf="lxc.cgroup.cpuset.cpus = 0,1"
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**--log-driver**="|*json-file*|*syslog*|*journald*|*gelf*|*fluentd*|*awslogs*|*splunk*|*none*"
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Logging driver for container. Default is defined by daemon `--log-driver` flag.
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**Warning**: the `docker logs` command works only for the `json-file` and
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`journald` logging drivers.
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**--log-opt**=[]
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Logging driver specific options.
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**-m**, **--memory**=""
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Memory limit (format: <number>[<unit>], where unit = b, k, m or g)
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Allows you to constrain the memory available to a container. If the host
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supports swap memory, then the **-m** memory setting can be larger than physical
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RAM. If a limit of 0 is specified (not using **-m**), the container's memory is
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not limited. The actual limit may be rounded up to a multiple of the operating
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system's page size (the value would be very large, that's millions of trillions).
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**--memory-reservation**=""
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Memory soft limit (format: <number>[<unit>], where unit = b, k, m or g)
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After setting memory reservation, when the system detects memory contention
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or low memory, containers are forced to restrict their consumption to their
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reservation. So you should always set the value below **--memory**, otherwise the
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hard limit will take precedence. By default, memory reservation will be the same
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as memory limit.
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**--memory-swap**=""
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Total memory limit (memory + swap)
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Set `-1` to disable swap (format: <number>[<unit>], where unit = b, k, m or g).
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This value should always larger than **-m**, so you should always use this with **-m**.
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**--mac-address**=""
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Container MAC address (e.g. 92:d0:c6:0a:29:33)
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Remember that the MAC address in an Ethernet network must be unique.
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The IPv6 link-local address will be based on the device's MAC address
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according to RFC4862.
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**--name**=""
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Assign a name to the container
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The operator can identify a container in three ways:
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UUID long identifier (“f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778”)
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UUID short identifier (“f78375b1c487”)
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Name (“jonah”)
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The UUID identifiers come from the Docker daemon, and if a name is not assigned
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to the container with **--name** then the daemon will also generate a random
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string name. The name is useful when defining links (see **--link**) (or any
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other place you need to identify a container). This works for both background
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and foreground Docker containers.
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**--net**="bridge"
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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. Note: the host mode gives the container full access to local system services such as D-bus and is therefore considered insecure.
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**--oom-kill-disable**=*true*|*false*
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Whether to disable OOM Killer for the container or not.
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**-P**, **--publish-all**=*true*|*false*
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Publish all exposed ports to random ports on the host interfaces. The default is *false*.
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When set to true publish all exposed ports to the host interfaces. The
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default is false. If the operator uses -P (or -p) then Docker will make the
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exposed port accessible on the host and the ports will be available to any
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client that can reach the host. When using -P, Docker will bind any exposed
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port to a random port on the host within an *ephemeral port range* defined by
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`/proc/sys/net/ipv4/ip_local_port_range`. To find the mapping between the host
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ports and the exposed ports, use `docker port`.
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**-p**, **--publish**=[]
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Publish a container's port, or range of ports, to the host.
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Format: `ip:hostPort:containerPort | ip::containerPort | hostPort:containerPort | containerPort`
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Both hostPort and containerPort can be specified as a range of ports.
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When specifying ranges for both, the number of container ports in the range must match the number of host ports in the range.
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(e.g., `docker run -p 1234-1236:1222-1224 --name thisWorks -t busybox`
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but not `docker run -p 1230-1236:1230-1240 --name RangeContainerPortsBiggerThanRangeHostPorts -t busybox`)
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With ip: `docker run -p 127.0.0.1:$HOSTPORT:$CONTAINERPORT --name CONTAINER -t someimage`
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Use `docker port` to see the actual mapping: `docker port CONTAINER $CONTAINERPORT`
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**--pid**=host
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Set the PID mode for the container
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**host**: use the host's PID namespace inside the container.
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Note: the host mode gives the container full access to local PID and is therefore considered insecure.
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**--uts**=host
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Set the UTS mode for the container
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**host**: use the host's UTS namespace inside the container.
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Note: the host mode gives the container access to changing the host's hostname and is therefore considered insecure.
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**--privileged**=*true*|*false*
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Give extended privileges to this container. The default is *false*.
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By default, Docker containers are
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“unprivileged” (=false) and cannot, for example, run a Docker daemon inside the
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Docker container. This is because by default a container is not allowed to
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access any devices. A “privileged” container is given access to all devices.
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When the operator executes **docker run --privileged**, Docker will enable access
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to all devices on the host as well as set some configuration in AppArmor to
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allow the container nearly all the same access to the host as processes running
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outside of a container on the host.
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**--read-only**=*true*|*false*
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Mount the container's root filesystem as read only.
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By default a container will have its root filesystem writable allowing processes
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to write files anywhere. By specifying the `--read-only` flag the container will have
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its root filesystem mounted as read only prohibiting any writes.
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**--restart**="no"
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Restart policy to apply when a container exits (no, on-failure[:max-retry], always, unless-stopped).
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**--rm**=*true*|*false*
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Automatically remove the container when it exits (incompatible with -d). The default is *false*.
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**--security-opt**=[]
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Security Options
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"label:user:USER" : Set the label user for the container
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"label:role:ROLE" : Set the label role for the container
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"label:type:TYPE" : Set the label type for the container
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"label:level:LEVEL" : Set the label level for the container
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"label:disable" : Turn off label confinement for the container
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**--stop-signal**=SIGTERM
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Signal to stop a container. Default is SIGTERM.
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**--sig-proxy**=*true*|*false*
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Proxy received signals to the process (non-TTY mode only). SIGCHLD, SIGSTOP, and SIGKILL are not proxied. The default is *true*.
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**--memory-swappiness**=""
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Tune a container's memory swappiness behavior. Accepts an integer between 0 and 100.
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**-t**, **--tty**=*true*|*false*
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Allocate a pseudo-TTY. The default is *false*.
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When set to true Docker can allocate a pseudo-tty and attach to the standard
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input of any container. This can be used, for example, to run a throwaway
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interactive shell. The default is false.
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The **-t** option is incompatible with a redirection of the docker client
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standard input.
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**-u**, **--user**=""
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Sets the username or UID used and optionally the groupname or GID for the specified command.
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The followings examples are all valid:
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--user [user | user:group | uid | uid:gid | user:gid | uid:group ]
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||
Without this argument the command will be run as root in the container.
|
||
|
||
""--ulimit""=[]
|
||
Ulimit options
|
||
|
||
**-v**, **--volume**=[] Create a bind mount
|
||
(format: `[host-dir:]container-dir[:<suffix options>]`, where suffix options
|
||
are comma delimited and selected from [rw|ro] and [z|Z].)
|
||
|
||
(e.g., using -v /host-dir:/container-dir, bind mounts /host-dir in the
|
||
host to /container-dir in the Docker container)
|
||
|
||
If 'host-dir' is missing, then docker automatically creates the new volume
|
||
on the host. **This auto-creation of the host path has been deprecated in
|
||
Release: v1.9.**
|
||
|
||
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.
|
||
|
||
The volume may be optionally suffixed with :ro or :rw to mount the volumes in
|
||
read-only or read-write mode, respectively. By default, the volumes are mounted
|
||
read-write. See examples.
|
||
|
||
Labeling systems like SELinux require that proper labels are placed on volume
|
||
content mounted into a container. Without a label, the security system might
|
||
prevent the processes running inside the container from using the content. By
|
||
default, Docker does not change the labels set by the OS.
|
||
|
||
To change a label in the container context, you can add either of two suffixes
|
||
`:z` or `:Z` to the volume mount. These suffixes tell Docker to relabel file
|
||
objects on the shared volumes. The `z` option tells Docker that two containers
|
||
share the volume content. As a result, Docker labels the content with a shared
|
||
content label. Shared volume labels allow all containers to read/write content.
|
||
The `Z` option tells Docker to label the content with a private unshared label.
|
||
Only the current container can use a private volume.
|
||
|
||
The `container-dir` must always be an absolute path such as `/src/docs`.
|
||
The `host-dir` can either be an absolute path or a `name` value. If you
|
||
supply an absolute path for the `host-dir`, Docker bind-mounts to the path
|
||
you specify. If you supply a `name`, Docker creates a named volume by that `name`.
|
||
|
||
A `name` value must start with start with an alphanumeric character,
|
||
followed by `a-z0-9`, `_` (underscore), `.` (period) or `-` (hyphen).
|
||
An absolute path starts with a `/` (forward slash).
|
||
|
||
For example, you can specify either `/foo` or `foo` for a `host-dir` value.
|
||
If you supply the `/foo` value, Docker creates a bind-mount. If you supply
|
||
the `foo` specification, Docker creates a named volume.
|
||
|
||
**--volumes-from**=[]
|
||
Mount volumes from the specified container(s)
|
||
|
||
Mounts already mounted volumes from a source container onto another
|
||
container. You must supply the source's container-id. To share
|
||
a volume, use the **--volumes-from** option when running
|
||
the target container. You can share volumes even if the source container
|
||
is not running.
|
||
|
||
By default, Docker mounts the volumes in the same mode (read-write or
|
||
read-only) as it is mounted in the source container. Optionally, you
|
||
can change this by suffixing the container-id with either the `:ro` or
|
||
`:rw ` keyword.
|
||
|
||
If the location of the volume from the source container overlaps with
|
||
data residing on a target container, then the volume hides
|
||
that data on the target.
|
||
|
||
**-w**, **--workdir**=""
|
||
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.
|
||
|
||
# Exit Status
|
||
|
||
The exit code from `docker run` gives information about why the container
|
||
failed to run or why it exited. When `docker run` exits with a non-zero code,
|
||
the exit codes follow the `chroot` standard, see below:
|
||
|
||
**_125_** if the error is with Docker daemon **_itself_**
|
||
|
||
$ docker run --foo busybox; echo $?
|
||
# flag provided but not defined: --foo
|
||
See 'docker run --help'.
|
||
125
|
||
|
||
**_126_** if the **_contained command_** cannot be invoked
|
||
|
||
$ docker run busybox /etc; echo $?
|
||
# exec: "/etc": permission denied
|
||
docker: Error response from daemon: Contained command could not be invoked
|
||
126
|
||
|
||
**_127_** if the **_contained command_** cannot be found
|
||
|
||
$ docker run busybox foo; echo $?
|
||
# exec: "foo": executable file not found in $PATH
|
||
docker: Error response from daemon: Contained command not found or does not exist
|
||
127
|
||
|
||
**_Exit code_** of **_contained command_** otherwise
|
||
|
||
$ docker run busybox /bin/sh -c 'exit 3'
|
||
# 3
|
||
|
||
# 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 /dev/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
|
||
|
||
## Sharing IPC between containers
|
||
|
||
Using shm_server.c available here: https://www.cs.cf.ac.uk/Dave/C/node27.html
|
||
|
||
Testing `--ipc=host` mode:
|
||
|
||
Host shows a shared memory segment with 7 pids attached, happens to be from httpd:
|
||
|
||
```
|
||
$ sudo ipcs -m
|
||
|
||
------ Shared Memory Segments --------
|
||
key shmid owner perms bytes nattch status
|
||
0x01128e25 0 root 600 1000 7
|
||
```
|
||
|
||
Now run a regular container, and it correctly does NOT see the shared memory segment from the host:
|
||
|
||
```
|
||
$ docker run -it shm ipcs -m
|
||
|
||
------ Shared Memory Segments --------
|
||
key shmid owner perms bytes nattch status
|
||
```
|
||
|
||
Run a container with the new `--ipc=host` option, and it now sees the shared memory segment from the host httpd:
|
||
|
||
```
|
||
$ docker run -it --ipc=host shm ipcs -m
|
||
|
||
------ Shared Memory Segments --------
|
||
key shmid owner perms bytes nattch status
|
||
0x01128e25 0 root 600 1000 7
|
||
```
|
||
Testing `--ipc=container:CONTAINERID` mode:
|
||
|
||
Start a container with a program to create a shared memory segment:
|
||
```
|
||
$ docker run -it shm bash
|
||
$ sudo shm/shm_server &
|
||
$ sudo ipcs -m
|
||
|
||
------ Shared Memory Segments --------
|
||
key shmid owner perms bytes nattch status
|
||
0x0000162e 0 root 666 27 1
|
||
```
|
||
Create a 2nd container correctly shows no shared memory segment from 1st container:
|
||
```
|
||
$ docker run shm ipcs -m
|
||
|
||
------ Shared Memory Segments --------
|
||
key shmid owner perms bytes nattch status
|
||
```
|
||
|
||
Create a 3rd container using the new --ipc=container:CONTAINERID option, now it shows the shared memory segment from the first:
|
||
|
||
```
|
||
$ docker run -it --ipc=container:ed735b2264ac shm ipcs -m
|
||
$ sudo ipcs -m
|
||
|
||
------ Shared Memory Segments --------
|
||
key shmid owner perms bytes nattch status
|
||
0x0000162e 0 root 666 27 1
|
||
```
|
||
|
||
## 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.
|
||
|
||
If a container is connected to the default bridge network and `linked`
|
||
with other containers, then the container's `/etc/hosts` file is updated
|
||
with the linked container's name.
|
||
|
||
> **Note** Since Docker may live update the container’s `/etc/hosts` file, there
|
||
may be situations when processes inside the container can end up reading an
|
||
empty or incomplete `/etc/hosts` file. In most cases, retrying the read again
|
||
should fix the problem.
|
||
|
||
|
||
## 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 intermediary
|
||
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.
|
||
|
||
## Using alternative security labeling
|
||
|
||
You can override the default labeling scheme for each container by specifying
|
||
the `--security-opt` flag. For example, you can specify the MCS/MLS level, a
|
||
requirement for MLS systems. Specifying the level in the following command
|
||
allows you to share the same content between containers.
|
||
|
||
# docker run --security-opt label:level:s0:c100,c200 -i -t fedora bash
|
||
|
||
An MLS example might be:
|
||
|
||
# docker run --security-opt label:level:TopSecret -i -t rhel7 bash
|
||
|
||
To disable the security labeling for this container versus running with the
|
||
`--permissive` flag, use the following command:
|
||
|
||
# docker run --security-opt label:disable -i -t fedora bash
|
||
|
||
If you want a tighter security policy on the processes within a container,
|
||
you can specify an alternate type for the container. You could run a container
|
||
that is only allowed to listen on Apache ports by executing the following
|
||
command:
|
||
|
||
# docker run --security-opt label:type:svirt_apache_t -i -t centos bash
|
||
|
||
Note:
|
||
|
||
You would have to write policy defining a `svirt_apache_t` type.
|
||
|
||
# HISTORY
|
||
April 2014, Originally compiled by William Henry (whenry at redhat dot com)
|
||
based on docker.com source material and internal work.
|
||
June 2014, updated by Sven Dowideit <SvenDowideit@home.org.au>
|
||
July 2014, updated by Sven Dowideit <SvenDowideit@home.org.au>
|
||
November 2015, updated by Sally O'Malley <somalley@redhat.com>
|