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Overview of kubectl

kubectl is a command line interface for running commands against Kubernetes clusters. This overview covers kubectl syntax, describes the command operations, and provides common examples. For details about each command, including all the supported flags and subcommands, see the kubectl reference documentation. For installation instructions see installing kubectl.

Syntax

Use the following syntax to run kubectl commands from your terminal window:

kubectl [command] [TYPE] [NAME] [flags]

where command, TYPE, NAME, and flags are:

• command: Specifies the operation that you want to perform on one or more resources, for example create, get, describe, delete.

• TYPE: Specifies the resource type. Resource types are case-sensitive and you can specify the singular, plural, or abbreviated forms. For example, the following commands produce the same output:

  $ kubectl get pod pod1
  $ kubectl get pods pod1
  $ kubectl get po pod1
  

• NAME: Specifies the name of the resource. Names are case-sensitive. If the name is omitted, details for all resources are displayed, for example $ kubectl get pods.

  When performing an operation on multiple resources, you can specify each resource by type and name or specify one or more files:

  • To specify resources by type and name:

    • To group resources if they are all the same type: TYPE1 name1 name2 name<#>.
      Example: $ kubectl get pod example-pod1 example-pod2

    • To specify multiple resource types individually: TYPE1/name1 TYPE1/name2 TYPE2/name3 TYPE<#>/name<#>.
      Example: $ kubectl get pod/example-pod1 replicationcontroller/example-rc1

  • To specify resources with one or more files: -f file1 -f file2 -f file<#>

    • Use YAML rather than JSON since YAML tends to be more user-friendly, especially for configuration files.
      Example: $ kubectl get pod -f ./pod.yaml

• flags: Specifies optional flags. For example, you can use the -s or --server flags to specify the address and port of the Kubernetes API server.
  Important: Flags that you specify from the command line override default values and any corresponding environment variables.

If you need help, just run kubectl help from the terminal window.

Operations

The following table includes short descriptions and the general syntax for all of the kubectl operations:

Remember: For more about command operations, see the kubectl reference documentation.

Resource types

The following table includes a list of all the supported resource types and their abbreviated aliases:

Output options

Use the following sections for information about how you can format or sort the output of certain commands. For details about which commands support the various output options, see the kubectl reference documentation.

Formatting output

The default output format for all kubectl commands is the human readable plain-text format. To output details to your terminal window in a specific format, you can add either the -o or -output flags to a supported kubectl command.

Syntax

kubectl [command] [TYPE] [NAME] -o=<output_format>

Depending on the kubectl operation, the following output formats are supported:

Example

In this example, the following command outputs the details for a single pod as a YAML formatted object:

$ kubectl get pod web-pod-13je7 -o=yaml

Remember: See the kubectl reference documentation for details about which output format is supported by each command.

Custom columns

To define custom columns and output only the details that you want into a table, you can use the custom-columns option. You can choose to define the custom columns inline or use a template file: -o=custom-columns=<spec> or -o=custom-columns-file=<filename>.

Examples

Inline:

$ kubectl get pods <pod-name> -o=custom-columns=NAME:.metadata.name,RSRC:.metadata.resourceVersion

Template file:

$ kubectl get pods <pod-name> -o=custom-columns-file=template.txt

where the template.txt file contains:

NAME                    RSRC
      metadata.name           metadata.resourceVersion

The result of running either command is:

NAME           RSRC
submit-queue   610995

Sorting list objects

To output objects to a sorted list in your terminal window, you can add the --sort-by flag to a supported kubectl command. Sort your objects by specifying any numeric or string field with the --sort-by flag. To specify a field, use a jsonpath expression.

Syntax

kubectl [command] [TYPE] [NAME] --sort-by=<jsonpath_exp>

Example

To print a list of pods sorted by name, you run:

$ kubectl get pods --sort-by=.metadata.name

Examples: Common operations

Use the following set of examples to help you familiarize yourself with running the commonly used kubectl operations:

kubectl create - Create a resource from a file or stdin.

// Create a service using the definition in example-service.yaml.
$ kubectl create -f example-service.yaml

// Create a replication controller using the definition in example-controller.yaml.
$ kubectl create -f example-controller.yaml

// Create the objects that are defined in any .yaml, .yml, or .json file within the <directory> directory.
$ kubectl create -f <directory>

kubectl get - List one or more resources.

// List all pods in plain-text output format.
$ kubectl get pods

// List all pods in plain-text output format and includes additional information (such as node name).
$ kubectl get pods -o wide

// List the replication controller with the specified name in plain-text output format. Tip: You can shorten and replace the 'replicationcontroller' resource type with the alias 'rc'.
$ kubectl get replicationcontroller <rc-name>

// List all replication controllers and services together in plain-text output format.
$ kubectl get rc,services

// List all daemon sets, including uninitialized ones, in plain-text output format.
$ kubectl get ds --include-uninitialized

// List all pods running on node server01
$ kubectl get pods --field-selector=spec.nodeName=server01

kubectl describe - Display detailed state of one or more resources, including the uninitialized ones by default.

// Display the details of the node with name <node-name>.
$ kubectl describe nodes <node-name>

// Display the details of the pod with name <pod-name>.
$ kubectl describe pods/<pod-name>

// Display the details of all the pods that are managed by the replication controller named <rc-name>.
// Remember: Any pods that are created by the replication controller get prefixed with the name of the replication controller.
$ kubectl describe pods <rc-name>

// Describe all pods, not including uninitialized ones
$ kubectl describe pods --include-uninitialized=false

Note: The kubectl get command is usually used for retrieving one or more resources of the same resource type. It features a rich set of flags that allows you to customize the output format using the -o or --output flag, for example. You can specify the -w or --watch flag to start watching updates to a particular object. The kubectl describe command is more focused on describing the many related aspects of a specified resource. It may invoke several API calls to the API server to build a view for the user. For example, the kubectl describe node command retrieves not only the information about the node, but also a summary of the pods running on it, the events generated for the node etc.

kubectl delete - Delete resources either from a file, stdin, or specifying label selectors, names, resource selectors, or resources.

// Delete a pod using the type and name specified in the pod.yaml file.
$ kubectl delete -f pod.yaml

// Delete all the pods and services that have the label name=<label-name>.
$ kubectl delete pods,services -l name=<label-name>

// Delete all the pods and services that have the label name=<label-name>, including uninitialized ones.
$ kubectl delete pods,services -l name=<label-name> --include-uninitialized

// Delete all pods, including uninitialized ones.
$ kubectl delete pods --all

kubectl exec - Execute a command against a container in a pod.

// Get output from running 'date' from pod <pod-name>. By default, output is from the first container.
$ kubectl exec <pod-name> date

// Get output from running 'date' in container <container-name> of pod <pod-name>.
$ kubectl exec <pod-name> -c <container-name> date

// Get an interactive TTY and run /bin/bash from pod <pod-name>. By default, output is from the first container.
$ kubectl exec -ti <pod-name> /bin/bash

kubectl logs - Print the logs for a container in a pod.

// Return a snapshot of the logs from pod <pod-name>.
$ kubectl logs <pod-name>

// Start streaming the logs from pod <pod-name>. This is similar to the 'tail -f' Linux command.
$ kubectl logs -f <pod-name>

Next steps

Start using the kubectl commands.