Kubernetes v1.17 [stable]
This page shows how to configure process namespace sharing for a pod. When process namespace sharing is enabled, processes in a container are visible to all other containers in that pod.
You can use this feature to configure cooperating containers, such as a log handler sidecar container, or to troubleshoot container images that don't include debugging utilities like a shell.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:
Your Kubernetes server must be at or later than version v1.10. To check the version, enterkubectl version
. Process Namespace Sharing is enabled using the shareProcessNamespace
field of v1.PodSpec
. For example:
Create the pod nginx
on your cluster:
kubectl apply -f https://k8s.io/examples/pods/share-process-namespace.yaml
Attach to the shell
container and run ps
:
kubectl attach -it nginx -c shell
If you don't see a command prompt, try pressing enter.
/ # ps ax
PID USER TIME COMMAND
1 root 0:00 /pause
8 root 0:00 nginx: master process nginx -g daemon off;
14 101 0:00 nginx: worker process
15 root 0:00 sh
21 root 0:00 ps ax
You can signal processes in other containers. For example, send SIGHUP
to nginx to restart the worker process. This requires the SYS_PTRACE
capability.
/ # kill -HUP 8
/ # ps ax
PID USER TIME COMMAND
1 root 0:00 /pause
8 root 0:00 nginx: master process nginx -g daemon off;
15 root 0:00 sh
22 101 0:00 nginx: worker process
23 root 0:00 ps ax
It's even possible to access another container image using the /proc/$pid/root
link.
/ # head /proc/8/root/etc/nginx/nginx.conf
user nginx;
worker_processes 1;
error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
Pods share many resources so it makes sense they would also share a process namespace. Some container images may expect to be isolated from other containers, though, so it's important to understand these differences:
The container process no longer has PID 1. Some container images refuse to start without PID 1 (for example, containers using systemd
) or run commands like kill -HUP 1
to signal the container process. In pods with a shared process namespace, kill -HUP 1
will signal the pod sandbox. (/pause
in the above example.)
Processes are visible to other containers in the pod. This includes all information visible in /proc
, such as passwords that were passed as arguments or environment variables. These are protected only by regular Unix permissions.
Container filesystems are visible to other containers in the pod through the /proc/$pid/root
link. This makes debugging easier, but it also means that filesystem secrets are protected only by filesystem permissions.
© 2022 The Kubernetes Authors
Documentation Distributed under CC BY 4.0.
https://kubernetes.io/docs/tasks/configure-pod-container/share-process-namespace/