Debugging Kubernetes nodes with crictl

FEATURE STATE: Kubernetes v1.11 [stable]

crictl is a command-line interface for CRI-compatible container runtimes. You can use it to inspect and debug container runtimes and applications on a Kubernetes node. crictl and its source are hosted in the cri-tools repository.

Before you begin

crictl requires a Linux operating system with a CRI runtime.

Installing crictl

You can download a compressed archive crictl from the cri-tools release page, for several different architectures. Download the version that corresponds to your version of Kubernetes. Extract it and move it to a location on your system path, such as /usr/local/bin/.

General usage

The crictl command has several subcommands and runtime flags. Use crictl help or crictl <subcommand> help for more details.

You can set the endpoint for crictl by doing one of the following:

  • Set the --runtime-endpoint and --image-endpoint flags.
  • Set the CONTAINER_RUNTIME_ENDPOINT and IMAGE_SERVICE_ENDPOINT environment variables.
  • Set the endpoint in the configuration file /etc/crictl.yaml. To specify a different file, use the --config=PATH_TO_FILE flag when you run crictl.

Note: If you don’t set an endpoint, crictl attempts to connect to a list of known endpoints, which might result in an impact to performance.

You can also specify timeout values when connecting to the server and enable or disable debugging, by specifying timeout or debug values in the configuration file or using the --timeout and --debug command-line flags.

To view or edit the current configuration, view or edit the contents of /etc/crictl.yaml. For example, the configuration when using the containerd container runtime would be similar to this:

  1. runtime-endpoint: unix:///var/run/containerd/containerd.sock
  2. image-endpoint: unix:///var/run/containerd/containerd.sock
  3. timeout: 10
  4. debug: true

To learn more about crictl, refer to the crictl documentation.

Example crictl commands

The following examples show some crictl commands and example output.

Warning: If you use crictl to create pod sandboxes or containers on a running Kubernetes cluster, the Kubelet will eventually delete them. crictl is not a general purpose workflow tool, but a tool that is useful for debugging.

List pods

List all pods:

  1. crictl pods

The output is similar to this:

  1. POD ID              CREATED              STATE               NAME                         NAMESPACE           ATTEMPT
  2. 926f1b5a1d33a       About a minute ago   Ready               sh-84d7dcf559-4r2gq          default             0
  3. 4dccb216c4adb       About a minute ago   Ready               nginx-65899c769f-wv2gp       default             0
  4. a86316e96fa89       17 hours ago         Ready               kube-proxy-gblk4             kube-system         0
  5. 919630b8f81f1       17 hours ago         Ready               nvidia-device-plugin-zgbbv   kube-system         0

List pods by name:

  1. crictl pods --name nginx-65899c769f-wv2gp

The output is similar to this:

  1. POD ID              CREATED             STATE               NAME                     NAMESPACE           ATTEMPT
  2. 4dccb216c4adb       2 minutes ago       Ready               nginx-65899c769f-wv2gp   default             0

List pods by label:

  1. crictl pods --label run=nginx

The output is similar to this:

  1. POD ID              CREATED             STATE               NAME                     NAMESPACE           ATTEMPT
  2. 4dccb216c4adb       2 minutes ago       Ready               nginx-65899c769f-wv2gp   default             0

List images

List all images:

  1. crictl images

The output is similar to this:

  1. IMAGE                                     TAG                 IMAGE ID            SIZE
  2. busybox                                   latest              8c811b4aec35f       1.15MB
  3. k8s-gcrio.azureedge.net/hyperkube-amd64   v1.10.3             e179bbfe5d238       665MB
  4. k8s-gcrio.azureedge.net/pause-amd64       3.1                 da86e6ba6ca19       742kB
  5. nginx                                     latest              cd5239a0906a6       109MB

List images by repository:

  1. crictl images nginx

The output is similar to this:

  1. IMAGE               TAG                 IMAGE ID            SIZE
  2. nginx               latest              cd5239a0906a6       109MB

Only list image IDs:

  1. crictl images -q

The output is similar to this:

  1. sha256:8c811b4aec35f259572d0f79207bc0678df4c736eeec50bc9fec37ed936a472a
  2. sha256:e179bbfe5d238de6069f3b03fccbecc3fb4f2019af741bfff1233c4d7b2970c5
  3. sha256:da86e6ba6ca197bf6bc5e9d900febd906b133eaa4750e6bed647b0fbe50ed43e
  4. sha256:cd5239a0906a6ccf0562354852fae04bc5b52d72a2aff9a871ddb6bd57553569

List containers

List all containers:

  1. crictl ps -a

The output is similar to this:

  1. CONTAINER ID        IMAGE                                                                                                             CREATED             STATE               NAME                       ATTEMPT
  2. 1f73f2d81bf98       busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47                                   7 minutes ago       Running             sh                         1
  3. 9c5951df22c78       busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47                                   8 minutes ago       Exited              sh                         0
  4. 87d3992f84f74       nginx@sha256:d0a8828cccb73397acb0073bf34f4d7d8aa315263f1e7806bf8c55d8ac139d5f                                     8 minutes ago       Running             nginx                      0
  5. 1941fb4da154f       k8s-gcrio.azureedge.net/hyperkube-amd64@sha256:00d814b1f7763f4ab5be80c58e98140dfc69df107f253d7fdd714b30a714260a   18 hours ago        Running             kube-proxy                 0

List running containers:

  1. crictl ps

The output is similar to this:

  1. CONTAINER ID        IMAGE                                                                                                             CREATED             STATE               NAME                       ATTEMPT
  2. 1f73f2d81bf98       busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47                                   6 minutes ago       Running             sh                         1
  3. 87d3992f84f74       nginx@sha256:d0a8828cccb73397acb0073bf34f4d7d8aa315263f1e7806bf8c55d8ac139d5f                                     7 minutes ago       Running             nginx                      0
  4. 1941fb4da154f       k8s-gcrio.azureedge.net/hyperkube-amd64@sha256:00d814b1f7763f4ab5be80c58e98140dfc69df107f253d7fdd714b30a714260a   17 hours ago        Running             kube-proxy                 0

Execute a command in a running container

  1. crictl exec -i -t 1f73f2d81bf98 ls

The output is similar to this:

  1. bin   dev   etc   home  proc  root  sys   tmp   usr   var

Get a container’s logs

Get all container logs:

  1. crictl logs 87d3992f84f74

The output is similar to this:

  1. 10.240.0.96 - - [06/Jun/2018:02:45:49 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.47.0" "-"
  2. 10.240.0.96 - - [06/Jun/2018:02:45:50 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.47.0" "-"
  3. 10.240.0.96 - - [06/Jun/2018:02:45:51 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.47.0" "-"

Get only the latest N lines of logs:

  1. crictl logs --tail=1 87d3992f84f74

The output is similar to this:

  1. 10.240.0.96 - - [06/Jun/2018:02:45:51 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.47.0" "-"

Run a pod sandbox

Using crictl to run a pod sandbox is useful for debugging container runtimes. On a running Kubernetes cluster, the sandbox will eventually be stopped and deleted by the Kubelet.

  1. Create a JSON file like the following:

    1. {
    2.   "metadata": {
    3.     "name": "nginx-sandbox",
    4.     "namespace": "default",
    5.     "attempt": 1,
    6.     "uid": "hdishd83djaidwnduwk28bcsb"
    7.   },
    8.   "log_directory": "/tmp",
    9.   "linux": {
    10.   }
    11. }

  2. Use the crictl runp command to apply the JSON and run the sandbox.

    1. crictl runp pod-config.json

    The ID of the sandbox is returned.

Create a container

Using crictl to create a container is useful for debugging container runtimes. On a running Kubernetes cluster, the sandbox will eventually be stopped and deleted by the Kubelet.

  1. Pull a busybox image

    1. crictl pull busybox
    1. Image is up to date for busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47

  2. Create configs for the pod and the container:

    Pod config:

    1. {
    2.   "metadata": {
    3.     "name": "busybox-sandbox",
    4.     "namespace": "default",
    5.     "attempt": 1,
    6.     "uid": "aewi4aeThua7ooShohbo1phoj"
    7.   },
    8.   "log_directory": "/tmp",
    9.   "linux": {
    10.   }
    11. }

    Container config:

    1. {
    2.   "metadata": {
    3.     "name": "busybox"
    4.   },
    5.   "image":{
    6.     "image": "busybox"
    7.   },
    8.   "command": [
    9.     "top"
    10.   ],
    11.   "log_path":"busybox.log",
    12.   "linux": {
    13.   }
    14. }

  3. Create the container, passing the ID of the previously-created pod, the container config file, and the pod config file. The ID of the container is returned.

    1. crictl create f84dd361f8dc51518ed291fbadd6db537b0496536c1d2d6c05ff943ce8c9a54f container-config.json pod-config.json

  4. List all containers and verify that the newly-created container has its state set to Created.

    1. crictl ps -a

    The output is similar to this:

    1. CONTAINER ID        IMAGE               CREATED             STATE               NAME                ATTEMPT
    2. 3e025dd50a72d       busybox             32 seconds ago      Created             busybox             0

Start a container

To start a container, pass its ID to crictl start:

  1. crictl start 3e025dd50a72d956c4f14881fbb5b1080c9275674e95fb67f965f6478a957d60

The output is similar to this:

  1. 3e025dd50a72d956c4f14881fbb5b1080c9275674e95fb67f965f6478a957d60

Check the container has its state set to Running.

  1. crictl ps

The output is similar to this:

  1. CONTAINER ID   IMAGE    CREATED              STATE    NAME     ATTEMPT
  2. 3e025dd50a72d  busybox  About a minute ago   Running  busybox  0

What’s next