How-To Query Container Mounts Using Crictl or Nerdctl

Problem

You want to list the mounts from each container without needing to exec into the container.

Environment

• Platform9 Managed Kubernetes - All Versions
• Containerd

Procedure

1. List the containers running on the node using the crictl or nerdctl utility pre-installed on the node.

Javascript

# /opt/pf9/pf9-kube/bin/crictl -r unix:///run/containerd/containerd.sock ps
CONTAINER           IMAGE               CREATED             STATE               NAME                      ATTEMPT             POD ID
68484121d71d1       0e9462c49c897       22 hours ago        Running             pf9-addon-operator        0                   31ce653d2a519
.........

# /opt/pf9/pf9-kube/bin/nerdctl -n k8s.io ps -a
CONTAINER ID    IMAGE                                                      COMMAND                   CREATED         STATUS     PORTS    NAMES
62d00aca415d    gcr.io/etcd-development/etcd:v3.4.14                       "/usr/local/bin/etcd"     25 hours ago    Up                  etcd
.......

1. Find the PID of the container

Javascript

# /opt/pf9/pf9-kube/bin/crictl -r unix:///run/containerd/containerd.sock inspect --output go-template --template '{{.info.pid}}' <container_ID>
28389

# /opt/pf9/pf9-kube/bin/nerdctl -n k8s.io inspect <container_ID> --format '{{.State.Pid}}'
21129

1. Query the /proc filesystem to find the mount information for each container.

Javascript

# cat /proc/28389/mountinfo
749 656 0:169 / / rw,relatime master:116 - overlay overlay rw,seclabel,lowerdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3360/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3359/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3358/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3277/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3276/fs,upperdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3512/fs,workdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/3512/work
750 749 0:171 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
751 749 0:172 / /dev rw,nosuid - tmpfs tmpfs rw,seclabel,size=65536k,mode=755
......