A context is a way of easily referring to a particular place that you want to run containers. You can set up a context and refer to
it by name, and easily switch between different contexts, so you can use containers in different places.
The most important commands for working with a context are
- `docker context create` will create a new context from options specified on the command line
- `docker context rm` removes a context
- `docker context use` will set the context to use by default; you can also use `docker --context ...` or via the environment with `DOCKER_CONTEXT=... docker ...`
- `docker context show` shows the context name that you are currently using.
- `docker context ls` lists the available contexts
- `docker context login` some types of context require credentials that may expire, such as OAuth credentials. If the credentials have
expired you will need to use `docker context login` to refresh them.
In addition you can use
- `docker context inspect` to see the full details of a context
- `docker context import` to import a context NOTE may make changes here, why can't create create from a file etc?
- `docker context export` to output a context NOTE may make changes here
## docker context create
To create a new context from options specified on the command line use `docker context create`. The exact information you need
to create a context depends on the particular backend.
NOTE for compatibility we may need to support existing syntax as well, but this should be deprecated. This may be a case where there are few users so can just change it.
Usage:
```
docker context create _name__type_ [options]
docker context create _name_ url
```
NOTE we could also use `docker context create _type_ _name_` might be more consistent, makes the url form less clear.
--dns-search value Set custom DNS search domains (default [])
--domainname string Container NIS domain name
--entrypoint string Overwrite the default ENTRYPOINT of the image
-e, --env value Set environment variables (default [])
--env-file value Read in a file of environment variables (default [])
--expose value Expose a port or a range of ports (default [])
--group-add value Add additional groups to join (default [])
--health-cmd string Command to run to check health
--health-interval duration Time between running the check (ns|us|ms|s|m|h) (default 0s)
--health-retries int Consecutive failures needed to report unhealthy
--health-timeout duration Maximum time to allow one check to run (ns|us|ms|s|m|h) (default 0s)
--health-start-period duration Start period for the container to initialize before counting retries towards unstable (ns|us|ms|s|m|h) (default 0s)
--help Print usage
-h, --hostname string Container host name
--init Run an init inside the container that forwards signals and reaps processes
-i, --interactive Keep STDIN open even if not attached
--io-maxbandwidth string Maximum IO bandwidth limit for the system drive (Windows only)
(Windows only). The format is `<number><unit>`.
Unit is optional and can be `b` (bytes per second),
`k` (kilobytes per second), `m` (megabytes per second),
or `g` (gigabytes per second). If you omit the unit,
the system uses bytes per second.
--io-maxbandwidth and --io-maxiops are mutually exclusive options.
--io-maxiops uint Maximum IOps limit for the system drive (Windows only)
--ip string IPv4 address (e.g., 172.30.100.104)
--ip6 string IPv6 address (e.g., 2001:db8::33)
--ipc string IPC namespace to use
--isolation string Container isolation technology
--kernel-memory string Kernel memory limit
-l, --label value Set meta data on a container (default [])
--label-file value Read in a line delimited file of labels (default [])
--link value Add link to another container (default [])
--link-local-ip value Container IPv4/IPv6 link-local addresses (default [])
--log-driver string Logging driver for the container
--log-opt value Log driver options (default [])
--mac-address string Container MAC address (e.g., 92:d0:c6:0a:29:33)
-m, --memory string Memory limit
--memory-reservation string Memory soft limit
--memory-swap string Swap limit equal to memory plus swap: '-1' to enable unlimited swap
--memory-swappiness int Tune container memory swappiness (0 to 100) (default -1)
--mount value Attach a filesystem mount to the container (default [])
--name string Assign a name to the container
--network-alias value Add network-scoped alias for the container (default [])
--network string Connect a container to a network
'bridge': create a network stack on the default Docker bridge
'none': no networking
'container:<name|id>': reuse another container's network stack
'host': use the Docker host network stack
'<network-name>|<network-id>': connect to a user-defined network
--no-healthcheck Disable any container-specified HEALTHCHECK
--oom-kill-disable Disable OOM Killer
--oom-score-adj int Tune host's OOM preferences (-1000 to 1000)
--pid string PID namespace to use
--pids-limit int Tune container pids limit (set -1 for unlimited)
--privileged Give extended privileges to this container
-p, --publish value Publish a container's port(s) to the host (default [])
-P, --publish-all Publish all exposed ports to random ports
--read-only Mount the container's root filesystem as read only
--restart string Restart policy to apply when a container exits (default "no")
Possible values are : no, on-failure[:max-retry], always, unless-stopped
--rm Automatically remove the container when it exits
--runtime string Runtime to use for this container
--security-opt value Security Options (default [])
--shm-size bytes Size of /dev/shm
The format is `<number><unit>`. `number` must be greater than `0`.
Unit is optional and can be `b` (bytes), `k` (kilobytes), `m` (megabytes),
or `g` (gigabytes). If you omit the unit, the system uses bytes.
--sig-proxy Proxy received signals to the process (default true)
--stop-signal string Signal to stop a container (default "SIGTERM")
--stop-timeout=10 Timeout (in seconds) to stop a container
--storage-opt value Storage driver options for the container (default [])
--sysctl value Sysctl options (default map[])
--tmpfs value Mount a tmpfs directory (default [])
-t, --tty Allocate a pseudo-TTY
--ulimit value Ulimit options (default [])
-u, --user string Username or UID (format: <name|uid>[:<group|gid>])
--userns string User namespace to use
'host': Use the Docker host user namespace
'': Use the Docker daemon user namespace specified by `--userns-remap` option.
--uts string UTS namespace to use
-v, --volume value Bind mount a volume (default []). The format
is `[host-src:]container-dest[:<options>]`.
The comma-delimited `options` are [rw|ro],
[z|Z], [[r]shared|[r]slave|[r]private],
[delegated|cached|consistent], and
[nocopy]. The 'host-src' is an absolute path
or a name value.
--volume-driver string Optional volume driver for the container
--volumes-from value Mount volumes from the specified container(s) (default [])
-w, --workdir string Working directory inside the container
```
## Description
The `docker run` command first `creates` a writeable container layer over the
specified image, and then `starts` it using the specified command. That is,
`docker run` is equivalent to the API `/containers/create` then
`/containers/(id)/start`. A stopped container can be restarted with all its
previous changes intact using `docker start`. See `docker ps -a` to view a list
of all containers.
The `docker run` command can be used in combination with `docker commit` to
[*change the command that a container runs*](commit.md). There is additional detailed information about `docker run` in the [Docker run reference](../run.md).
For information on connecting a container to a network, see the ["*Docker network overview*"](https://docs.docker.com/engine/userguide/networking/).
## Examples
### Assign name and allocate pseudo-TTY (--name, -it)
```bash
$ docker run --name test -it debian
root@d6c0fe130dba:/# exit 13
$ echo $?
13
$ 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.
In the example, the `bash` shell is quit by entering
`exit 13`. This exit code is passed on to the caller of
`docker run`, and is recorded in the `test` container's metadata.
### Capture container ID (--cidfile)
```bash
$ docker run --cidfile /tmp/docker_test.cid ubuntu echo "test"
```
This will create a container and print `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 will return an error. Docker will close this
file when `docker run` exits.
### Full container capabilities (--privileged)
```bash
$ docker run -t -i --rm ubuntu bash
root@bc338942ef20:/# mount -t tmpfs none /mnt
mount: permission denied
```
This will *not* work, because by default, most potentially dangerous kernel
capabilities are dropped; including `cap_sys_admin` (which is required to mount
filesystems). However, the `--privileged` flag will allow it to run:
```bash
$ 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)
```bash
$ docker run -w /path/to/dir/ -i -t ubuntu pwd
```
The `-w` lets the command being executed inside directory given, here
`/path/to/dir/`. If the path does not exist it is created inside the container.
### Set storage driver options per container
```bash
$ docker run -it --storage-opt size=120G fedora /bin/bash
```
This (size) will allow to set the container rootfs size to 120G at creation time.
This option is only available for the `devicemapper`, `btrfs`, `overlay2`,
`windowsfilter` and `zfs` graph drivers.
For the `devicemapper`, `btrfs`, `windowsfilter` and `zfs` graph drivers,
user cannot pass a size less than the Default BaseFS Size.
For the `overlay2` storage driver, the size option is only available if the
backing fs is `xfs` and mounted with the `pquota` mount option.
Under these conditions, user can pass any size less than the backing fs size.
### Mount tmpfs (--tmpfs)
```bash
$ 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`,
| `no` | Do 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-stopped` | Restart the container unless it is explicitly stopped or Docker itself is stopped or restarted. |
| `always` | Always restart the container regardless of the exit status. When you specify always, the Docker daemon will try to restart the container indefinitely. The container will also always start on daemon startup, regardless of the current state of the container. |
```bash
$ docker run --restart=always redis
```
This will run the `redis` container with a restart policy of **always**
so that if the container exits, Docker will restart it.
More detailed information on restart policies can be found in the
- With `hyperv` isolation, Windows will create 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."
Justin Cormack
Christopher Crone