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Container Command and Arguments

In the configuration file for a Container, you can set the command and args fields to override the default Entrypoint and Cmd of the the Container’s image.

Container entry points and arguments
What’s next

Container entry points and arguments

The configuration file for a Container has an image field that specifies the Docker image to be run in the Container. A Docker image has metadata that includes a default Entrypoint and a default Cmd.

When Kubernetes starts a Container, it runs the image’s default Entrypoint and passes the image’s default Cmd as arguments.

If you want override the image’s default Entrypoint and Cmd, you can use the command and args fields in the Container’s configuration.

The command field specifies the actual command run by the Container.
The args field specifies the arguments passed to the command.

This table summarizes the field names used by Docker and Kubernetes.

Description	Docker field name	Kubernetes field name
The command run by the container	Entrypoint	command
The arguments passed to the command	Cmd	args

Here’s an example of a configuration file for a Pod that has one Container.

`commands.yaml`
`apiVersion: v1 kind: Pod metadata: name: command-demo labels: purpose: demonstrate-command spec: containers: - name: command-demo-container image: debian command: ["printenv"] args: ["HOSTNAME", "KUBERNETES_PORT"]`

commands.yaml Copy commands.yaml to clipboard

apiVersion: v1
kind: Pod
metadata:
  name: command-demo
  labels:
    purpose: demonstrate-command
spec:
  containers:
  - name: command-demo-container
    image: debian
    command: ["printenv"]
    args: ["HOSTNAME", "KUBERNETES_PORT"]

When Kubernetes starts the Container, it runs this command:

printenv HOSTNAME KUBERNETES_PORT

When you override the default Entrypoint and Cmd, these rules apply:

If you do not supply command or args for a Container, the defaults defined in the Docker image are used.
If you supply a command but no args for a Container, only the supplied command is used. The default EntryPoint and the default Cmd defined in the Docker image are ignored.
If you supply only args for a Container, the default Entrypoint defined in the Docker image is run with the args that you supplied.
If you supply a command and args, the default Entrypoint and the default Cmd defined in the Docker image are ignored. Your command is run with your args.

Here are some examples:

Image Entrypoint	Image Cmd	Container command	Container args	Command run
`[/ep-1]`	`[foo bar]`	<not set>	<not set>	`[ep-1 foo bar]`
`[/ep-1]`	`[foo bar]`	`[/ep-2]`	<not set>	`[ep-2]`
`[/ep-1]`	`[foo bar]`	<not set>	`[zoo boo]`	`[ep-1 zoo boo]`
`[/ep-1]`	`[foo bar]`	`[/ep-2]`	`[zoo boo]`	`[ep-2 zoo boo]`

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