List Kubernetes Namespaces With kubectl

In Kubernetes, namespaces provide a logical way to separate resources within an application, forming isolated virtual clusters within the Kubernetes cluster. For example, you can create namespaces for the development  and production  environments and manage their resources independently.

The short answer

To list all the namespaces in your Kubernetes cluster at once, you can use the kubectl get namespaces  command:

 $ kubectl get namespaces

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This command provides details for every Namespace within your cluster including their status and age.

Where:

• NAME  is the unique name of the namespace.
• STATUS  is the current state of the namespace such as Active , NotFound , etc.
• AGE  is the time when the namespace was created.

If you want to learn more about namespaces, you can read our article on how to create a namespace in Kubernetes with kubectl.

Easily retrieve this command using Warp’s AI Command Suggestions

If you’re using Warp as your terminal, you can easily retrieve this command using the Warp AI Command Suggestions feature:

Entering k8s list namespaces  (Kubernetes is abbreviated as "k8s") in the AI Command Suggestions will prompt a kubectl  command that can then quickly be inserted into your shell by doing CMD+ENTER .

Listing namespaces by name

To list one or more namespaces by name in your Kubernetes cluster, you can use the kubectl get namespaces  command as follows:

 $ kubectl get namespaces <namespace_name …>

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Where:

• namespace_name …  is a list of namespace names separated by a space character.

For example:

 $ kubectl get namespaces namespace1 namespace2

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Upon execution, the above command will output a table of information about the Namespaces named namespace1  and namespace2 , including their name, status, and age. 

Note that, if you specify a namespace name that does not exist, the command will output an error indicating that the specified namespace was not found. 

Listing namespaces by label

Labels are key-value pairs attached to the Kubernetes objects that organize resources based on specific criteria. By default, Kubernetes sets a default label for all namespaces kubernetes.io/metadata.name  with the value of the namespace name.

To list namespaces based on a specific label, you can use the kubectl get namespaces  command with the -l  flag (short for --label ):

 $ kubectl get namespaces -l <label>=<value>

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Where:

• label  is the key of the label.
• value  is the value associated with the label.

For example:

 $ kubectl get namespaces -l app=myapp

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Upon execution, the above command will display all namespaces with the label app=myapp  assigned to them. 

Displaying the labels of all namespaces

To view the labels associated with all the namespaces at once, you can use the kubectl get namespaces  command with the --show-label  flag:

 $ kubectl get namespaces --show-labels

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Upon execution, the above command will output an additional column showing any labels associated with namespaces.

Listing namespaces in the YAML or JSON formats

By default, the output format of the kubectl get namespaces  command is a table. However, you can specify other formats, such as YAML or JSON using the -o  flag (short for --output ):

 $ kubectl get namespaces -o <output_format>

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Where:

• output_format  is one of yaml  or json .

For example:

 $ kubectl get namespaces -o yaml

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Upon execution, the above command will display comprehensive details about all the namespaces in the specified YAML format.

Filtering namespaces using a field selector

To filter the list of namespaces based on a specific field, you can use the kubectl get namespaces  command with the --field-selector  flag:

 $ kubectl get namespaces --field-selector=<field_name>=<field_value>

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Where:

• field_name  is a JSONPath expression used for selecting a specific field.
• field_value  is the value for the specified field.

For example, this command will filter and display the list of all active namespaces:

 $ kubectl get namespaces --field-selector=status.phase=Active

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You can learn more about JSONPath expressions by visiting the official Kubernetes documentation page.

Sorting the output of the kubectl get namespaces  command

To sort the output of the kubectl get namespaces  command based on a specific field, you can use the kubectl get namespaces  command with the --sort-by  flag:

 $ kubectl get namespaces --sort-by=<expression>

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Where:

• expression  is a JSONPath expression.

For example, this command will display the list of all namespaces sorted by their names in ascending order:

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

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Customizing the output of the kubectl get namespaces  command

To customize the output columns of the kubectl get namespaces  command, you can use the kubectl get namespaces  command with the -o custom-columns flag:

 $ kubectl get namespaces -o custom-columns=<custom_column_name>:<expression>

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Where:

• custom_column_name  is the name you want to assign to a column.
• expression  is a JSONPath expression.

For example:

 $ kubectl get namespaces -o custom-columns='NAME:.metadata.name,SPEC.FINALIZER:.spec.finalizers[0]'

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Upon execution, the above command will output two columns, NAME  populated with the values of metadata.name  and SPEC.FINALIZER  populated with the first values of the spec.finalizers . 

Customizing the output using a template file

To customize the output columns of the kubectl get namespaces  command using a template file (i.e. a predefined column configuration), you can use the -o custom-column-file  flag:

 $ kubectl get namespaces -o custom-columns-file=<template_file_path>

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Where: template_file_path  is an absolute or relative file path for a template file.

For example:

 $ kubectl get namespaces -o custom-columns-file=./myTemplate.txt

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Where the myTemplate.txt  file contains:

 NAME                 SPEC.FINALIZER
metadata.name  spec.finalizers[0]

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Upon execution, the above command will output two columns NAME  populated with the values of metadata.name  and SPEC.FINALIZER  populated with the first values of the spec.finalizers . 

Extracting namespace information

To output specific field values of namespaces, you can use the kubectl get namespaces  command with the -o  flag combined with a JSONPath expression as follows:

 $ kubectl get namespaces -o jsonpath="<expression>"

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Where:

• expression  is a JSONPath expression

For example, this command will extract the key-value pairs of each label assigned to the Namespace:

 $ kubectl get namespaces -o=jsonpath="{.items[*].metadata.labels}"

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Where:

• .items[*]  indicates to iterate over each Namespace.
• .metadata  specifies the Namespace metadata.
• labels  retrieves the label name.

Describe namespaces with additional information

To display additional information about the namespaces, you can use the kubectl describe namespaces  command as follows:

 $ kubectl describe namespaces <namespace_name …>

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Where:

• namespace_name …  is a list of Namespace names separated by a space indicator.

For example:

 $ kubectl describe namespaces my-app-namespace my-db-namespace

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Upon execution, the above command will output details about the Namespaces my-app-namespace  and my-db-namespace , such as associated labels, annotations, the status of the namespace, and more. 

To output details about all namespaces in the cluster, execute the following command without specifying namespace names:

 $ kubectl describe namespaces

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Listing pods, services or nodes by a namespace

To list Kubernetes resources (such as pods, nodes, services and more) by a specified namespace, you can use the kubectl get  command with the -n  flag (short for --namespace ) as follows:

 $ kubectl get <resource> -n <namespace>

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Where:

• resource  is the name of a Kubernetes resource such as pods, nodes, services, etc.
• namespace  is the name of a specific Namespace.

For example, the below command will output the list of all pods within the namespace named my-app-namespace :

 $ kubectl get pods -n my-app-namespace

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And the below command will output the list of all services within the namespace named my-app-namespace :

 $ kubectl get services -n my-app-namespace

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