Mountpoint Permission Cause Container Creation Error

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Understanding Container Creation Errors

When creating a container, Kubernetes uses a combination of configuration files and runtime environments to set up the container's file system and permissions. However, sometimes, container creation can fail due to permission issues with the mountpoint. In this article, we will explore the relationship between mountpoint permissions and container creation errors.

Security Context and Mountpoint Permissions

The security context of a pod is defined in the pod's YAML file. The security context includes settings such as allowPrivilegeEscalation, capabilities, runAsNonRoot, and runAsUser. These settings determine the permissions and behavior of the container.

In the provided YAML file, the security context is set as follows:

securityContext:
allowPrivilegeEscalation: false
capabilities:
drop:
- ALL
runAsNonRoot: true
runAsUser: 1000480000

This configuration sets the container to run as a non-root user with no privileges.

Mountpoint Permissions and Container Creation

The mountpoint is the directory where the container's file system is mounted. The permissions of the mountpoint can affect container creation. In the provided example, the mountpoint's merged directory permissions are set to 700.

To determine the permissions of the merged directory in the mountpoint, we can use the crictl command to list the pods and then use the runc command to list the containers. We can then use the ls command to list the files in the mountpoint.

Here are the commands used to determine the permissions of the merged directory:

[root@1b0j5ykmfdg9s2cp 4bc8b54559ed4d76b9a9064353927282]# crictl pods |grep cke-service-controller-5d6bdb5d6-b544g
9456f0ac8fa90       15 hours ago        Ready               cke-service-controller-5d6bdb5d6-b544g                    ccos-product-cke                              0                   (default)

[root@1b0j5ykmfdg9s2cp 4bc8b54559ed4d76b9a9064353927282]# crictl ps -a |grep 9456f0ac8fa90
ca8053a1eb378       image.ccos.io/ceake/ceake@sha256:a39e456aaddb1c5a7cf376a841537594a873d651ca01506a457dac484bebf98c   15 hours ago        Exited              cke-service                                   0                   9456f0ac8fa90       cke-service-controller-5d6bdb5d6-b544g

[root@1b0j5ykmfdg9s2cp 4bc8b54559ed4d76b9a9064353927282]# runc -root /run/runc list |grep ca8053a1eb378
ca8053a1eb378fc20f82d51ff7ac60c6cb6ad150375ff93fb5ef671f4ebd4328   0           stopped     /run/containers/storage/overlay-containers/ca8053aeb378fc20f82d51ff7ac60c6cb6ad150375ff93fb5ef671f4ebd4328/userdata   2025-04-20T15:44:11.648919703Z   root

[root@1b0j5ykmfdg9s2cp 4bc8b54559ed4d76b9a9064353927282]# cat /run/containers/storage/overlay-containers/ca8053a1eb378fc20f82d51ff7ac60c6cb6ad150375ff93fb5ef671f4ebd4328/userdata/config.json |jq |grep -i m
ountpoint
    "io.kubernetes.cri-o.MountPoint": "/data/ceake/imagefs/overlay/3b06894c6d15df0c0936b97a3d9f029067375ac00f0fb9895943a4b7873bc0d9/merged",

[root@1b0j5ykmfdg9s2cp 4bc8b54559ed4d76b9a9064353927282]# ls -alhZ /data/ceake/imagefs/overlay/3b06894c6d15df0c0936b97a3d9f029067375ac00f0fb9895943a4b7873bc0d9/
total 100K
drwx------.   5 root root system_u:object_r:unlabeled_t:s0      69 Apr 20 23:44 .
drwxr-xr-x. 850 root root unconfined_u:object_r:unlabeled_t:s0 72K Apr 21 14:11 ..
dr-xr-xr-x.   5 root root system_u:object_r:unlabeled_t:s0      39 Apr 20 23:44 diff
-rw-r--r--.   1 root root system_u:object_r:unlabeled_t:s0      26 Apr 20 23:44 link
-rw-r--r--.   1 root root system_u:object_r:unlabeled_t:s0      86 Apr 20 23:44 lower
drwx------.   2 root root system_u:object_r:unlabeled_t:s0       6 Apr 20 23:44 merged
drwx------.   3 root root system_u:object_r:unlabeled_t:s0      18 Apr 20 23:44 work

[root@1b0j5ykmfdg9s2cp ~]# umask
0022

The output of the ls command shows that the merged directory has permissions of 700, which is a problem because the container is configured to run as a non-root user with no privileges.

Conclusion

In this article, we have explored the relationship between mountpoint permissions and container creation errors. We have seen that the security context of a pod can affect the permissions of the mountpoint, and that the permissions of the mountpoint can affect container creation.

To resolve the issue, we need to ensure that the permissions of the mountpoint are set correctly. We can do this by setting the umask value to a value that allows the container to write to the mountpoint.

Here is an example of how to set the umask value:

[root@1b0j5ykmfdg92cp ~]# umask 022

This sets the umask value to 022, which allows the container to write to the mountpoint.

By setting the umask value correctly, we can ensure that the container can write to the mountpoint and that container creation is successful.

Recommendations

  1. Set the umask value correctly: Ensure that the umask value is set to a value that allows the container to write to the mountpoint.
  2. Check the security context: Check the security context of the pod to ensure that it is set correctly.
  3. Check the mountpoint permissions: Check the permissions of the mountpoint to ensure that they are set correctly.
  4. Use a tool like crictl: Use a tool like crictl to list the pods and containers and to check the permissions of the mountpoint.

Q: What is the relationship between mountpoint permissions and container creation errors?

A: The mountpoint permissions can affect container creation. If the mountpoint permissions are set to a value that prevents the container from writing to the mountpoint, container creation will fail.

Q: How do I determine the permissions of the merged directory in the mountpoint?

A: You can use the crictl command to list the pods and then use the runc command to list the containers. You can then use the ls command to list the files in the mountpoint.

Q: What is the umask value and how does it affect container creation?

A: The umask value is a setting that determines the permissions of new files and directories. If the umask value is set to a value that prevents the container from writing to the mountpoint, container creation will fail.

Q: How do I set the umask value correctly?

A: You can set the umask value using the umask command. For example, you can set the umask value to 022 using the following command:

[root@1b0j5ykmfdg92cp ~]# umask 022

Q: What is the security context and how does it affect container creation?

A: The security context is a setting that determines the permissions and behavior of the container. If the security context is set to a value that prevents the container from writing to the mountpoint, container creation will fail.

Q: How do I check the security context of a pod?

A: You can check the security context of a pod by looking at the pod's YAML file. The security context is typically defined in the securityContext section of the YAML file.

Q: What are some common mistakes that can cause container creation errors?

A: Some common mistakes that can cause container creation errors include:

  • Setting the umask value to a value that prevents the container from writing to the mountpoint
  • Setting the security context to a value that prevents the container from writing to the mountpoint
  • Not setting the umask value correctly
  • Not checking the security context of the pod

Q: How can I troubleshoot container creation errors?

A: You can troubleshoot container creation errors by:

  • Checking the umask value and security context of the pod
  • Checking the permissions of the mountpoint
  • Using tools like crictl and runc to list the pods and containers and to check the permissions of the mountpoint
  • Checking the logs of the container for any error messages

Q: What are some best practices for setting up container creation?

A: Some best practices for setting up container creation include:

  • Setting the umask value correctly
  • Setting the security context correctly
  • Checking the permissions of the mountpoint
  • Using tools like crictl and runc to list the pods and containers and to the permissions of the mountpoint
  • Checking the logs of the container for any error messages

By following these best practices and troubleshooting common mistakes, you can ensure that container creation is successful and that the container can write to the mountpoint.