website/content/en/docs/reference/kubectl/overview.md

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reviewers	title
bgrant0607 hw-qiaolei	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-insensitive and you can specify the singular, plural, or abbreviated forms. For example, the following commands produce the same output:

  ```shell
  $ 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:

Operation	Syntax	Description
annotate	kubectl annotate (-f FILENAME | TYPE NAME | TYPE/NAME) KEY_1=VAL_1 ... KEY_N=VAL_N [--overwrite] [--all] [--resource-version=version] [flags]	Add or update the annotations of one or more resources.
api-versions	kubectl api-versions [flags]	List the API versions that are available.
apply	kubectl apply -f FILENAME [flags]	Apply a configuration change to a resource from a file or stdin.
attach	kubectl attach POD -c CONTAINER [-i] [-t] [flags]	Attach to a running container either to view the output stream or interact with the container (stdin).
autoscale	kubectl autoscale (-f FILENAME | TYPE NAME | TYPE/NAME) [--min=MINPODS] --max=MAXPODS [--cpu-percent=CPU] [flags]	Automatically scale the set of pods that are managed by a replication controller.
cluster-info	kubectl cluster-info [flags]	Display endpoint information about the master and services in the cluster.
config	kubectl config SUBCOMMAND [flags]	Modifies kubeconfig files. See the individual subcommands for details.
create	kubectl create -f FILENAME [flags]	Create one or more resources from a file or stdin.
delete	kubectl delete (-f FILENAME | TYPE [NAME | /NAME | -l label | --all]) [flags]	Delete resources either from a file, stdin, or specifying label selectors, names, resource selectors, or resources.
describe	kubectl describe (-f FILENAME | TYPE [NAME_PREFIX | /NAME | -l label]) [flags]	Display the detailed state of one or more resources.
edit	kubectl edit (-f FILENAME | TYPE NAME | TYPE/NAME) [flags]	Edit and update the definition of one or more resources on the server by using the default editor.
exec	kubectl exec POD [-c CONTAINER] [-i] [-t] [flags] [-- COMMAND [args...]]	Execute a command against a container in a pod,
explain	kubectl explain [--include-extended-apis=true] [--recursive=false] [flags]	Get documentation of various resources. For instance pods, nodes, services, etc.
expose	kubectl expose (-f FILENAME | TYPE NAME | TYPE/NAME) [--port=port] [--protocol=TCP|UDP] [--target-port=number-or-name] [--name=name] [----external-ip=external-ip-of-service] [--type=type] [flags]	Expose a replication controller, service, or pod as a new Kubernetes service.
get	kubectl get (-f FILENAME | TYPE [NAME | /NAME | -l label]) [--watch] [--sort-by=FIELD] [[-o | --output]=OUTPUT_FORMAT] [flags]	List one or more resources.
label	kubectl label (-f FILENAME | TYPE NAME | TYPE/NAME) KEY_1=VAL_1 ... KEY_N=VAL_N [--overwrite] [--all] [--resource-version=version] [flags]	Add or update the labels of one or more resources.
logs	kubectl logs POD [-c CONTAINER] [--follow] [flags]	Print the logs for a container in a pod.
patch	kubectl patch (-f FILENAME | TYPE NAME | TYPE/NAME) --patch PATCH [flags]	Update one or more fields of a resource by using the strategic merge patch process.
port-forward	kubectl port-forward POD [LOCAL_PORT:]REMOTE_PORT [...[LOCAL_PORT_N:]REMOTE_PORT_N] [flags]	Forward one or more local ports to a pod.
proxy	kubectl proxy [--port=PORT] [--www=static-dir] [--www-prefix=prefix] [--api-prefix=prefix] [flags]	Run a proxy to the Kubernetes API server.
replace	kubectl replace -f FILENAME	Replace a resource from a file or stdin.
rolling-update	kubectl rolling-update OLD_CONTROLLER_NAME ([NEW_CONTROLLER_NAME] --image=NEW_CONTAINER_IMAGE | -f NEW_CONTROLLER_SPEC) [flags]	Perform a rolling update by gradually replacing the specified replication controller and its pods.
run	kubectl run NAME --image=image [--env="key=value"] [--port=port] [--replicas=replicas] [--dry-run=bool] [--overrides=inline-json] [flags]	Run a specified image on the cluster.
scale	kubectl scale (-f FILENAME | TYPE NAME | TYPE/NAME) --replicas=COUNT [--resource-version=version] [--current-replicas=count] [flags]	Update the size of the specified replication controller.
stop	kubectl stop	Deprecated: Instead, see kubectl delete.
version	kubectl version [--client] [flags]	Display the Kubernetes version running on the client and server.

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:

Resource type	Abbreviated alias
apiservices
certificatesigningrequests	csr
clusters
clusterrolebindings
clusterroles
componentstatuses	cs
configmaps	cm
controllerrevisions
cronjobs
customresourcedefinition	crd
daemonsets	ds
deployments	deploy
endpoints	ep
events	ev
horizontalpodautoscalers	hpa
ingresses	ing
jobs
limitranges	limits
namespaces	ns
networkpolicies	netpol
nodes	no
persistentvolumeclaims	pvc
persistentvolumes	pv
poddisruptionbudget	pdb
podpreset
pods	po
podsecuritypolicies	psp
podtemplates
replicasets	rs
replicationcontrollers	rc
resourcequotas	quota
rolebindings
roles
secrets
serviceaccounts	sa
services	svc
statefulsets
storageclasses

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:

Output format	Description
-o=custom-columns=<spec>	Print a table using a comma separated list of custom columns.
-o=custom-columns-file=<filename>	Print a table using the custom columns template in the <filename> file.
-o=json	Output a JSON formatted API object.
-o=jsonpath=<template>	Print the fields defined in a jsonpath expression.
-o=jsonpath-file=<filename>	Print the fields defined by the jsonpath expression in the <filename> file.
-o=name	Print only the resource name and nothing else.
-o=wide	Output in the plain-text format with any additional information. For pods, the node name is included.
-o=yaml	Output a YAML formatted API object.

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

Server-side columns

kubectl supports receiving specific column information from the server about objects. This means that for any given resource, the server will return columns and rows relevant to that resource, for the client to print. This allows for consistent human-readable output across clients used against the same cluster, by having the server encapsulate the details of printing.

This feature is enabled by default in kubectl 1.11 and higher. To disable it, add the --server-print=false flag to the kubectl get command.

Examples

To print information about the status of a pod, use a command like the following:

kubectl get pods <pod-name> --server-print=false

Output looks like this:

NAME       READY     STATUS              RESTARTS   AGE
pod-name   1/1       Running             0          1m

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

// List all pods in plain-text output format, delegating the details of printing to the server
$ kubectl get pods --experimental-server-print

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 >}} 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. {{< /note >}}

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>

Examples: Creating and using plugins

Use the following set of examples to help you familiarize yourself with writing and using kubectl plugins:

// create a simple plugin in any language and name the resulting executable file
// so that it begins with the prefix "kubectl-"
$ cat ./kubectl-hello
#!/bin/bash

# this plugin prints the words "hello world"
echo "hello world"

// with our plugin written, let's make it executable
$ sudo chmod +x ./kubectl-hello

// and move it to a location in our PATH
$ sudo mv ./kubectl-hello /usr/local/bin

// we have now created and "installed" a kubectl plugin.
// we can begin using our plugin by invoking it from kubectl as if it were a regular command
$ kubectl hello
hello world

// we can "uninstall" a plugin, by simply removing it from our PATH
$ sudo rm /usr/local/bin/kubectl-hello

In order to view all of the plugins that are available to kubectl, we can use the kubectl plugin list subcommand:

$ kubectl plugin list
The following kubectl-compatible plugins are available:

/usr/local/bin/kubectl-hello
/usr/local/bin/kubectl-foo
/usr/local/bin/kubectl-bar

// this command can also warn us about plugins that are
// not executable, or that are overshadowed by other
// plugins, for example
$ sudo chmod -x /usr/local/bin/kubectl-foo
$ kubectl plugin list
The following kubectl-compatible plugins are available:

/usr/local/bin/kubectl-hello
/usr/local/bin/kubectl-foo
  - warning: /usr/local/bin/kubectl-foo identified as a plugin, but it is not executable
/usr/local/bin/kubectl-bar

error: one plugin warning was found

We can think of plugins as a means to build more complex functionality on top of the existing kubectl commands:

$ cat ./kubectl-whoami
#!/bin/bash

# this plugin makes use of the `kubectl config` command in order to output
# information about the current user, based on the currently selected context
kubectl config view --template='{{ range .contexts }}{{ if eq .name "'$(kubectl config current-context)'" }}Current user: {{ .context.user }}{{ end }}{{ end }}'

Running the above plugin gives us an output containing the user for the currently selected context in our KUBECONFIG file:

// make the file executable
$ sudo chmod +x ./kubectl-whoami

// and move it into our PATH
$ sudo mv ./kubectl-whoami /usr/local/bin

$ kubectl whoami
Current user: plugins-user

To find out more about plugins, take a look at the example cli plugin.

Next steps

Start using the kubectl commands.