docker run

Create and run a new container from an image


docker run [OPTIONS] IMAGE [COMMAND] [ARG...]


The docker run command runs a command in a new container, pulling the image if needed and starting the container.

You can restart a stopped container with all its previous changes intact using docker start. Use docker ps -a to view a list of all containers, including those that are stopped.


--add-hostAdd a custom host-to-IP mapping (host:ip)
--annotationAPI 1.43+ Add an annotation to the container (passed through to the OCI runtime)
--attach-aAttach to STDIN, STDOUT or STDERR
--blkio-weightBlock IO (relative weight), between 10 and 1000, or 0 to disable (default 0)
--blkio-weight-deviceBlock IO weight (relative device weight)
--cap-addAdd Linux capabilities
--cap-dropDrop Linux capabilities
--cgroup-parentOptional parent cgroup for the container
--cgroupnsAPI 1.41+ Cgroup namespace to use (host|private) 'host': Run the container in the Docker host's cgroup namespace 'private': Run the container in its own private cgroup namespace '': Use the cgroup namespace as configured by the default-cgroupns-mode option on the daemon (default)
--cidfileWrite the container ID to the file
--cpu-countCPU count (Windows only)
--cpu-percentCPU percent (Windows only)
--cpu-periodLimit CPU CFS (Completely Fair Scheduler) period
--cpu-quotaLimit CPU CFS (Completely Fair Scheduler) quota
--cpu-rt-periodAPI 1.25+ Limit CPU real-time period in microseconds
--cpu-rt-runtimeAPI 1.25+ Limit CPU real-time runtime in microseconds
--cpu-shares-cCPU shares (relative weight)
--cpusAPI 1.25+ Number of CPUs
--cpuset-cpusCPUs in which to allow execution (0-3, 0,1)
--cpuset-memsMEMs in which to allow execution (0-3, 0,1)
--detach-dRun container in background and print container ID
--detach-keysOverride the key sequence for detaching a container
--deviceAdd a host device to the container
--device-cgroup-ruleAdd a rule to the cgroup allowed devices list
--device-read-bpsLimit read rate (bytes per second) from a device
--device-read-iopsLimit read rate (IO per second) from a device
--device-write-bpsLimit write rate (bytes per second) to a device
--device-write-iopsLimit write rate (IO per second) to a device
--disable-content-trusttrueSkip image verification
--dnsSet custom DNS servers
--dns-optSet DNS options
--dns-optionSet DNS options
--dns-searchSet custom DNS search domains
--domainnameContainer NIS domain name
--entrypointOverwrite the default ENTRYPOINT of the image
--env-eSet environment variables
--env-fileRead in a file of environment variables
--exposeExpose a port or a range of ports
--gpusAPI 1.40+ GPU devices to add to the container ('all' to pass all GPUs)
--group-addAdd additional groups to join
--health-cmdCommand to run to check health
--health-intervalTime between running the check (ms|s|m|h) (default 0s)
--health-retriesConsecutive failures needed to report unhealthy
--health-start-periodAPI 1.29+ Start period for the container to initialize before starting health-retries countdown (ms|s|m|h) (default 0s)
--health-timeoutMaximum time to allow one check to run (ms|s|m|h) (default 0s)
--helpPrint usage
--hostname-hContainer host name
--initAPI 1.25+ Run an init inside the container that forwards signals and reaps processes
--interactive-iKeep STDIN open even if not attached
--io-maxbandwidthMaximum IO bandwidth limit for the system drive (Windows only)
--io-maxiopsMaximum IOps limit for the system drive (Windows only)
--ipIPv4 address (e.g.,
--ip6IPv6 address (e.g., 2001:db8::33)
--ipcIPC mode to use
--isolationContainer isolation technology
--kernel-memoryKernel memory limit
--label-lSet meta data on a container
--label-fileRead in a line delimited file of labels
--linkAdd link to another container
--link-local-ipContainer IPv4/IPv6 link-local addresses
--log-driverLogging driver for the container
--log-optLog driver options
--mac-addressContainer MAC address (e.g., 92:d0:c6:0a:29:33)
--memory-mMemory limit
--memory-reservationMemory soft limit
--memory-swapSwap limit equal to memory plus swap: '-1' to enable unlimited swap
--memory-swappiness-1Tune container memory swappiness (0 to 100)
--mountAttach a filesystem mount to the container
--nameAssign a name to the container
--netConnect a container to a network
--net-aliasAdd network-scoped alias for the container
--networkConnect a container to a network
--network-aliasAdd network-scoped alias for the container
--no-healthcheckDisable any container-specified HEALTHCHECK
--oom-kill-disableDisable OOM Killer
--oom-score-adjTune host's OOM preferences (-1000 to 1000)
--pidPID namespace to use
--pids-limitTune container pids limit (set -1 for unlimited)
--platformAPI 1.32+ Set platform if server is multi-platform capable
--privilegedGive extended privileges to this container
--publish-pPublish a container's port(s) to the host
--publish-all-PPublish all exposed ports to random ports
--pullmissingPull image before running (always, missing, never)
--quiet-qSuppress the pull output
--read-onlyMount the container's root filesystem as read only
--restartnoRestart policy to apply when a container exits
--rmAutomatically remove the container when it exits
--runtimeRuntime to use for this container
--security-optSecurity Options
--shm-sizeSize of /dev/shm
--sig-proxytrueProxy received signals to the process
--stop-signalSignal to stop the container
--stop-timeoutAPI 1.25+ Timeout (in seconds) to stop a container
--storage-optStorage driver options for the container
--sysctlSysctl options
--tmpfsMount a tmpfs directory
--tty-tAllocate a pseudo-TTY
--ulimitUlimit options
--user-uUsername or UID (format: <name|uid>[:<group|gid>])
--usernsUser namespace to use
--utsUTS namespace to use
--volume-vBind mount a volume
--volume-driverOptional volume driver for the container
--volumes-fromMount volumes from the specified container(s)
--workdir-wWorking directory inside the container


Assign name and allocate pseudo-TTY (--name, -it)

$ docker run --name test -it debian

root@d6c0fe130dba:/# exit 13
$ echo $?
$ docker ps -a | grep test
d6c0fe130dba        debian:7            "/bin/bash"         26 seconds ago      Exited (13) 17 seconds ago                         test

This example runs a container named test using the debian:latest image. The -it instructs Docker to allocate a pseudo-TTY connected to the container's stdin; creating an interactive bash shell in the container. The example quits the bash shell by entering exit 13, passing the exit code on to the caller of docker run, and recording it in the test container's metadata.

Capture container ID (--cidfile)

$ docker run --cidfile /tmp/docker_test.cid ubuntu echo "test"

This creates a container and prints test to the console. The cidfile flag makes Docker attempt to create a new file and write the container ID to it. If the file exists already, Docker returns an error. Docker closes this file when docker run exits.

Full container capabilities (--privileged)

$ docker run -t -i --rm ubuntu bash
root@bc338942ef20:/# mount -t tmpfs none /mnt
mount: permission denied

This doesn't work, because by default, Docker drops most potentially dangerous kernel capabilities, including CAP_SYS_ADMIN (which is required to mount filesystems). However, the --privileged flag allows it to run:

$ docker run -t -i --privileged ubuntu bash
root@50e3f57e16e6:/# mount -t tmpfs none /mnt
root@50e3f57e16e6:/# df -h
Filesystem      Size  Used Avail Use% Mounted on
none            1.9G     0  1.9G   0% /mnt

The --privileged flag gives all capabilities to the container, and it also lifts all the limitations enforced by the device cgroup controller. In other words, the container can then do almost everything that the host can do. This flag exists to allow special use-cases, like running Docker within Docker.

Set working directory (-w, --workdir)

$ docker  run -w /path/to/dir/ -i -t  ubuntu pwd

The -w option runs the command executed inside the directory specified, in this example, /path/to/dir/. If the path does not exist, Docker creates it inside the container.

Set storage driver options per container (--storage-opt)

$ docker run -it --storage-opt size=120G fedora /bin/bash

This (size) constraints the container filesystem size to 120G at creation time. This option is only available for the devicemapper, btrfs, overlay2, windowsfilter and zfs storage drivers.

For the overlay2 storage driver, the size option is only available if the backing filesystem is xfs and mounted with the pquota mount option. Under these conditions, you can pass any size less than the backing filesystem size.

For the windowsfilter, devicemapper, btrfs, and zfs storage drivers, you cannot pass a size less than the Default BaseFS Size.

Mount tmpfs (--tmpfs)

$ docker run -d --tmpfs /run:rw,noexec,nosuid,size=65536k my_image

The --tmpfs flag mounts an empty tmpfs into the container with the rw, noexec, nosuid, size=65536k options.

Mount volume (-v)

$ docker  run  -v $(pwd):$(pwd) -w $(pwd) -i -t  ubuntu pwd

The example above mounts the current directory into the container at the same path using the -v flag, sets it as the working directory, and then runs the pwd command inside the container.

As of Docker Engine version 23, you can use relative paths on the host.

$ docker  run  -v ./content:/content -w /content -i -t  ubuntu pwd

The example above mounts the content directory in the current directory into the container at the /content path using the -v flag, sets it as the working directory, and then runs the pwd command inside the container.

$ docker run -v /doesnt/exist:/foo -w /foo -i -t ubuntu bash

When the host directory of a bind-mounted volume doesn't exist, Docker automatically creates this directory on the host for you. In the example above, Docker creates the /doesnt/exist folder before starting your container.

Mount volume read-only (--read-only)

$ docker run --read-only -v /icanwrite busybox touch /icanwrite/here

You can use volumes in combination with the --read-only flag to control where a container writes files. The --read-only flag mounts the container's root filesystem as read only prohibiting writes to locations other than the specified volumes for the container.

$ docker run -t -i -v /var/run/docker.sock:/var/run/docker.sock -v /path/to/static-docker-binary:/usr/bin/docker busybox sh

By bind-mounting the Docker Unix socket and statically linked Docker binary (refer to get the Linux binary), you give the container the full access to create and manipulate the host's Docker daemon.

On Windows, you must specify the paths using Windows-style path semantics.

PS C:\> docker run -v c:\foo:c:\dest microsoft/nanoserver cmd /s /c type c:\dest\somefile.txt
Contents of file

PS C:\> docker run -v c:\foo:d: microsoft/nanoserver cmd /s /c type d:\somefile.txt
Contents of file

The following examples fails when using Windows-based containers, as the destination of a volume or bind mount inside the container must be one of: a non-existing or empty directory; or a drive other than C:. Further, the source of a bind mount must be a local directory, not a file.

net use z: \\remotemachine\share
docker run -v z:\foo:c:\dest ...
docker run -v \\uncpath\to\directory:c:\dest ...
docker run -v c:\foo\somefile.txt:c:\dest ...
docker run -v c:\foo:c: ...
docker run -v c:\foo:c:\existing-directory-with-contents ...

For in-depth information about volumes, refer to manage data in containers

Add bind mounts or volumes using the --mount flag

The --mount flag allows you to mount volumes, host-directories, and tmpfs mounts in a container.

The --mount flag supports most options supported by the -v or the --volume flag, but uses a different syntax. For in-depth information on the --mount flag, and a comparison between --volume and --mount, refer to Bind mounts.

Even though there is no plan to deprecate --volume, usage of --mount is recommended.


$ docker run --read-only --mount type=volume,target=/icanwrite busybox touch /icanwrite/here
$ docker run -t -i --mount type=bind,src=/data,dst=/data busybox sh

Publish or expose port (-p, --expose)

$ docker run -p ubuntu bash

This binds port 8080 of the container to TCP port 80 on of the host machine. You can also specify udp and sctp ports. The Docker User Guide explains in detail how to use ports in Docker.

Note that ports which are not bound to the host (i.e., -p 80:80 instead of -p are externally accessible. This also applies if you configured UFW to block this specific port, as Docker manages its own iptables rules. Read more

$ docker run --expose 80 ubuntu bash

This exposes port 80 of the container without publishing the port to the host system's interfaces.

Set the pull policy (--pull)

Use the --pull flag to set the image pull policy when creating (and running) the container.

The --pull flag can take one of these values:

missing (default)Pull the image if it was not found in the image cache, or use the cached image otherwise.
neverDo not pull the image, even if it's missing, and produce an error if the image does not exist in the image cache.
alwaysAlways perform a pull before creating the container.

When creating (and running) a container from an image, the daemon checks if the image exists in the local image cache. If the image is missing, an error is returned to the CLI, allowing it to initiate a pull.

The default (missing) is to only pull the image if it's not present in the daemon's image cache. This default allows you to run images that only exist locally (for example, images you built from a Dockerfile, but that have not been pushed to a registry), and reduces networking.

The always option always initiates a pull before creating the container. This option makes sure the image is up-to-date, and prevents you from using outdated images, but may not be suitable in situations where you want to test a locally built image before pushing (as pulling the image overwrites the existing image in the image cache).

The never option disables (implicit) pulling images when creating containers, and only uses images that are available in the image cache. If the specified image is not found, an error is produced, and the container is not created. This option is useful in situations where networking is not available, or to prevent images from being pulled implicitly when creating containers.

The following example shows docker run with the --pull=never option set, which produces en error as the image is missing in the image-cache:

$ docker run --pull=never hello-world
docker: Error response from daemon: No such image: hello-world:latest.

Set environment variables (-e, --env, --env-file)

$ docker run -e MYVAR1 --env MYVAR2=foo --env-file ./env.list ubuntu bash

Use the -e, --env, and --env-file flags to set simple (non-array) environment variables in the container you're running, or overwrite variables defined in the Dockerfile of the image you're running.

You can define the variable and its value when running the container:

$ docker run --env VAR1=value1 --env VAR2=value2 ubuntu env | grep VAR

You can also use variables exported to your local environment:

export VAR1=value1
export VAR2=value2

$ docker run --env VAR1 --env VAR2 ubuntu env | grep VAR

When running the command, the Docker CLI client checks the value the variable has in your local environment and passes it to the container. If no = is provided and that variable is not exported in your local environment, the variable isn't set in the container.

You can also load the environment variables from a file. This file should use the syntax <variable>=value (which sets the variable to the given value) or <variable> (which takes the value from the local environment), and # for comments.

$ cat env.list
# This is a comment

$ docker run --env-file env.list ubuntu env | grep -E 'VAR|USER'

Set metadata on container (-l, --label, --label-file)

A label is a key=value pair that applies metadata to a container. To label a container with two labels:

$ docker run -l my-label --label ubuntu bash

The my-label key doesn't specify a value so the label defaults to an empty string (""). To add multiple labels, repeat the label flag (-l or --label).

The key=value must be unique to avoid overwriting the label value. If you specify labels with identical keys but different values, each subsequent value overwrites the previous. Docker uses the last key=value you supply.

Use the --label-file flag to load multiple labels from a file. Delimit each label in the file with an EOL mark. The example below loads labels from a labels file in the current directory:

$ docker run --label-file ./labels ubuntu bash

The label-file format is similar to the format for loading environment variables. (Unlike environment variables, labels are not visible to processes running inside a container.) The following example shows a label-file format:

com.example.label1="a label"

# this is a comment
com.example.label2=another\ label

You can load multiple label-files by supplying multiple --label-file flags.

For additional information on working with labels, see Labels - custom metadata in Docker in the Docker User Guide.

Connect a container to a network (--network)

To start a container and connect it to a network, use the --network option.

The following commands create a network named my-net and adds a busybox container to the my-net network.

$ docker network create my-net
$ docker run -itd --network=my-net busybox

You can also choose the IP addresses for the container with --ip and --ip6 flags when you start the container on a user-defined network. To assign a static IP to containers, you must specify subnet block for the network.

$ docker network create --subnet my-net
$ docker run -itd --network=my-net --ip= busybox

If you want to add a running container to a network use the docker network connect subcommand.

You can connect multiple containers to the same network. Once connected, the containers can communicate using only another container's IP address or name. For overlay networks or custom plugins that support multi-host connectivity, containers connected to the same multi-host network but launched from different Engines can also communicate in this way.


The default bridge network only allow containers to communicate with each other using internal IP addresses. User-created bridge networks provide DNS resolution between containers using container names.

You can disconnect a container from a network using the docker network disconnect command.

For more information on connecting a container to a network when using the run command, see the "Docker network overview".

Mount volumes from container (--volumes-from)

$ docker run --volumes-from 777f7dc92da7 --volumes-from ba8c0c54f0f2:ro -i -t ubuntu pwd

The --volumes-from flag mounts all the defined volumes from the referenced containers. You can specify more than one container by repetitions of the --volumes-from argument. The container ID may be optionally suffixed with :ro or :rw to mount the volumes in read-only or read-write mode, respectively. By default, Docker mounts the volumes in the same mode (read write or read only) as the reference container.

Labeling systems like SELinux require placing proper labels 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 the 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.

Attach to STDIN/STDOUT/STDERR (-a, --attach)

The --attach (or -a) flag tells docker run to bind to the container's STDIN, STDOUT or STDERR. This makes it possible to manipulate the output and input as needed.

$ echo "test" | docker run -i -a stdin ubuntu cat -

This pipes data into a container and prints the container's ID by attaching only to the container's STDIN.

$ docker run -a stderr ubuntu echo test

This isn't going to print anything to the console unless there's an error because output is only attached to the STDERR of the container. The container's logs still store what's written to STDERR and STDOUT.

$ cat somefile | docker run -i -a stdin mybuilder dobuild

This example shows a way of using --attach to pipe a file into a container. The command prints the container's ID after the build completes and you can retrieve the build logs using docker logs. This is useful if you need to pipe a file or something else into a container and retrieve the container's ID once the container has finished running.

See also the docker cp command.

Override the detach sequence (--detach-keys)

Use the --detach-keys option to override the Docker key sequence for detach. This is useful if the Docker default sequence conflicts with key sequence you use for other applications. There are two ways to define your own detach key sequence, as a per-container override or as a configuration property on your entire configuration.

To override the sequence for an individual container, use the --detach-keys="<sequence>" flag with the docker attach command. The format of the <sequence> is either a letter [a-Z], or the ctrl- combined with any of the following:

  • a-z (a single lowercase alpha character )
  • @ (at sign)
  • [ (left bracket)
  • \\ (two backward slashes)
  • _ (underscore)
  • ^ (caret)

These a, ctrl-a, X, or ctrl-\\ values are all examples of valid key sequences. To configure a different configuration default key sequence for all containers, see Configuration file section.

Add host device to container (--device)

$ docker run -it --rm \
    --device=/dev/sdc:/dev/xvdc \
    --device=/dev/sdd \
    --device=/dev/zero:/dev/foobar \
    ubuntu ls -l /dev/{xvdc,sdd,foobar}

brw-rw---- 1 root disk 8, 2 Feb  9 16:05 /dev/xvdc
brw-rw---- 1 root disk 8, 3 Feb  9 16:05 /dev/sdd
crw-rw-rw- 1 root root 1, 5 Feb  9 16:05 /dev/foobar

It's often necessary to directly expose devices to a container. The --device option enables that. For example, adding a specific block storage device or loop device or audio device to an otherwise unprivileged container (without the --privileged flag) and have the application directly access it.

By default, the container is able to read, write and mknod these devices. This can be overridden using a third :rwm set of options to each --device flag. If the container is running in privileged mode, then Docker ignores the specified permissions.

$ docker run --device=/dev/sda:/dev/xvdc --rm -it ubuntu fdisk  /dev/xvdc

Command (m for help): q
$ docker run --device=/dev/sda:/dev/xvdc:r --rm -it ubuntu fdisk  /dev/xvdc
You will not be able to write the partition table.

Command (m for help): q

$ docker run --device=/dev/sda:/dev/xvdc:rw --rm -it ubuntu fdisk  /dev/xvdc

Command (m for help): q

$ docker run --device=/dev/sda:/dev/xvdc:m --rm -it ubuntu fdisk  /dev/xvdc
fdisk: unable to open /dev/xvdc: Operation not permitted


The --device option cannot be safely used with ephemeral devices. You shouldn't add block devices that may be removed to untrusted containers with --device.

For Windows, the format of the string passed to the --device option is in the form of --device=<IdType>/<Id>. Beginning with Windows Server 2019 and Windows 10 October 2018 Update, Windows only supports an IdType of class and the Id as a device interface class GUIDopen_in_new. Refer to the table defined in the Windows container docsopen_in_new for a list of container-supported device interface class GUIDs.

If you specify this option for a process-isolated Windows container, Docker makes all devices that implement the requested device interface class GUID available in the container. For example, the command below makes all COM ports on the host visible in the container.

PS C:\> docker run --device=class/86E0D1E0-8089-11D0-9CE4-08003E301F73


The --device option is only supported on process-isolated Windows containers, and produces an error if the container isolation is hyperv.

Using dynamically created devices (--device-cgroup-rule)

Docker assigns devices available to a container at creation time. The assigned devices are added to the cgroup.allow file and created into the container when it runs. This poses a problem when you need to add a new device to running container.

One solution is to add a more permissive rule to a container allowing it access to a wider range of devices. For example, supposing the container needs access to a character device with major 42 and any number of minor numbers (added as new devices appear), add the following rule:

$ docker run -d --device-cgroup-rule='c 42:* rmw' -name my-container my-image

Then, a user could ask udev to execute a script that would docker exec my-container mknod newDevX c 42 <minor> the required device when it is added.

Note: You still need to explicitly add initially present devices to the docker run / docker create command.

Access an NVIDIA GPU

The --gpus flag allows you to access NVIDIA GPU resources. First you need to install the nvidia-container-runtimeopen_in_new.

Read Specify a container's resources for more information.

To use --gpus, specify which GPUs (or all) to use. If you provide no value, Docker uses all available GPUs. The example below exposes all available GPUs.

$ docker run -it --rm --gpus all ubuntu nvidia-smi

Use the device option to specify GPUs. The example below exposes a specific GPU.

$ docker run -it --rm --gpus device=GPU-3a23c669-1f69-c64e-cf85-44e9b07e7a2a ubuntu nvidia-smi

The example below exposes the first and third GPUs.

$ docker run -it --rm --gpus '"device=0,2"' nvidia-smi

Restart policies (--restart)

Use the --restart flag to specify a container's restart policy. A restart policy controls whether the Docker daemon restarts a container after exit. Docker supports the following restart policies:

noDo not automatically restart the container when it exits. This is the default.
on-failure[:max-retries]Restart only if the container exits with a non-zero exit status. Optionally, limit the number of restart retries the Docker daemon attempts.
unless-stoppedRestart the container unless it's explicitly stopped or Docker itself is stopped or restarted.
alwaysAlways restart the container regardless of the exit status. When you specify always, the Docker daemon tries to restart the container indefinitely. The container always starts on daemon startup, regardless of the current state of the container.
$ docker run --restart=always redis

This will run the redis container with a restart policy of always so that if the container exits, Docker restarts it.

You can find more detailed information on restart policies in the Restart Policies (--restart) section of the Docker run reference page.

Add entries to container hosts file (--add-host)

You can add other hosts into a container's /etc/hosts file by using one or more --add-host flags. This example adds a static address for a host named docker:

$ docker run --add-host=docker: --rm -it alpine

/ # ping docker
PING docker ( 56 data bytes
64 bytes from seq=0 ttl=37 time=93.052 ms
64 bytes from seq=1 ttl=37 time=92.467 ms
64 bytes from seq=2 ttl=37 time=92.252 ms
--- docker ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 92.209/92.495/93.052 ms

The --add-host flag supports a special host-gateway value that resolves to the internal IP address of the host. This is useful when you want containers to connect to services running on the host machine.

It's conventional to use host.docker.internal as the hostname referring to host-gateway. Docker Desktop automatically resolves this hostname, see Explore networking features.

The following example shows how the special host-gateway value works. The example runs an HTTP server that serves a file from host to container over the host.docker.internal hostname, which resolves to the host's internal IP.

$ echo "hello from host!" > ./hello
$ python3 -m http.server 8000
Serving HTTP on port 8000 ( ...
$ docker run \
  --add-host host.docker.internal:host-gateway \
  curlimages/curl -s host.docker.internal:8000/hello
hello from host!

Set ulimits in container (--ulimit)

Since setting ulimit settings in a container requires extra privileges not available in the default container, you can set these using the --ulimit flag. Specify --ulimit with a soft and hard limit in the format <type>=<soft limit>[:<hard limit>]. For example:

$ docker run --ulimit nofile=1024:1024 --rm debian sh -c "ulimit -n"


If you don't provide a hard limit value, Docker uses the soft limit value for both values. If you don't provide any values, they are inherited from the default ulimits set on the daemon.


The as option is deprecated. In other words, the following script is not supported:

$ docker run -it --ulimit as=1024 fedora /bin/bash

Docker sends the values to the appropriate OS syscall and doesn't perform any byte conversion. Take this into account when setting the values.

For nproc usage

Be careful setting nproc with the ulimit flag as Linux uses nproc to set the maximum number of processes available to a user, not to a container. For example, start four containers with daemon user:

$ docker run -d -u daemon --ulimit nproc=3 busybox top

$ docker run -d -u daemon --ulimit nproc=3 busybox top

$ docker run -d -u daemon --ulimit nproc=3 busybox top

$ docker run -d -u daemon --ulimit nproc=3 busybox top

The 4th container fails and reports a "[8] System error: resource temporarily unavailable" error. This fails because the caller set nproc=3 resulting in the first three containers using up the three processes quota set for the daemon user.

Stop container with signal (--stop-signal)

The --stop-signal flag sends the system call signal to the container to exit. This signal can be a signal name in the format SIG<NAME>, for instance SIGKILL, or an unsigned number that matches a position in the kernel's syscall table, for instance 9.

The default value is defined by STOPSIGNAL in the image, or SIGTERM if the image has no STOPSIGNAL defined.

Optional security options (--security-opt)

On Windows, you can use this flag to specify the credentialspec option. The credentialspec must be in the format file://spec.txt or registry://keyname.

Stop container with timeout (--stop-timeout)

The --stop-timeout flag sets the number of seconds to wait for the container to stop after sending the pre-defined (see --stop-signal) system call signal. If the container does not exit after the timeout elapses, it's forcibly killed with a SIGKILL signal.

If you set --stop-timeout to -1, no timeout is applied, and the daemon waits indefinitely for the container to exit.

The Daemon determines the default, and is 10 seconds for Linux containers, and 30 seconds for Windows containers.

Specify isolation technology for container (--isolation)

This option is useful in situations where you are running Docker containers on Windows. The --isolation=<value> option sets a container's isolation technology. On Linux, the only supported is the default option which uses Linux namespaces. These two commands are equivalent on Linux:

$ docker run -d busybox top
$ docker run -d --isolation default busybox top

On Windows, --isolation can take one of these values:

defaultUse the value specified by the Docker daemon's --exec-opt or system default (see below).
processShared-kernel namespace isolation.
hypervHyper-V hypervisor partition-based isolation.

The default isolation on Windows server operating systems is process, and hyperv on Windows client operating systems, such as Windows 10. Process isolation has better performance, but requires that the image and host use the same kernel version.

On Windows server, assuming the default configuration, these commands are equivalent and result in process isolation:

PS C:\> docker run -d microsoft/nanoserver powershell echo process
PS C:\> docker run -d --isolation default microsoft/nanoserver powershell echo process
PS C:\> docker run -d --isolation process microsoft/nanoserver powershell echo process

If you have set the --exec-opt isolation=hyperv option on the Docker daemon, or are running against a Windows client-based daemon, these commands are equivalent and result in hyperv isolation:

PS C:\> docker run -d microsoft/nanoserver powershell echo hyperv
PS C:\> docker run -d --isolation default microsoft/nanoserver powershell echo hyperv
PS C:\> docker run -d --isolation hyperv microsoft/nanoserver powershell echo hyperv

Specify hard limits on memory available to containers (-m, --memory)

These parameters always set an upper limit on the memory available to the container. Linux sets this on the cgroup and applications in a container can query it at /sys/fs/cgroup/memory/memory.limit_in_bytes.

On Windows, this affects containers differently depending on what type of isolation you use.

  • With process isolation, Windows reports the full memory of the host system, not the limit to applications running inside the container

    PS C:\> docker run -it -m 2GB --isolation=process microsoft/nanoserver powershell Get-ComputerInfo *memory*
    CsTotalPhysicalMemory      : 17064509440
    CsPhyicallyInstalledMemory : 16777216
    OsTotalVisibleMemorySize   : 16664560
    OsFreePhysicalMemory       : 14646720
    OsTotalVirtualMemorySize   : 19154928
    OsFreeVirtualMemory        : 17197440
    OsInUseVirtualMemory       : 1957488
    OsMaxProcessMemorySize     : 137438953344
  • With hyperv isolation, Windows creates a utility VM that is big enough to hold the memory limit, plus the minimal OS needed to host the container. That size is reported as "Total Physical Memory."

    PS C:\> docker run -it -m 2GB --isolation=hyperv microsoft/nanoserver powershell Get-ComputerInfo *memory*
    CsTotalPhysicalMemory      : 2683355136
    CsPhyicallyInstalledMemory :
    OsTotalVisibleMemorySize   : 2620464
    OsFreePhysicalMemory       : 2306552
    OsTotalVirtualMemorySize   : 2620464
    OsFreeVirtualMemory        : 2356692
    OsInUseVirtualMemory       : 263772
    OsMaxProcessMemorySize     : 137438953344

Configure namespaced kernel parameters (sysctls) at runtime (--sysctl)

The --sysctl sets namespaced kernel parameters (sysctls) in the container. For example, to turn on IP forwarding in the containers network namespace, run this command:

$ docker run --sysctl net.ipv4.ip_forward=1 someimage


Not all sysctls are namespaced. Docker does not support changing sysctls inside of a container that also modify the host system. As the kernel evolves we expect to see more sysctls become namespaced.

Currently supported sysctls

IPC Namespace:

  • kernel.msgmax, kernel.msgmnb, kernel.msgmni, kernel.sem, kernel.shmall, kernel.shmmax, kernel.shmmni, kernel.shm_rmid_forced.
  • Sysctls beginning with fs.mqueue.*
  • If you use the --ipc=host option these sysctls are not allowed.

Network Namespace:

  • Sysctls beginning with net.*
  • If you use the --network=host option using these sysctls are not allowed.