---
title: Common Issues
weight: 11120
indent: true
---

# Ceph Common Issues

Many of these problem cases are hard to summarize down to a short phrase that adequately describes the problem. Each problem will start with a bulleted list of symptoms. Keep in mind that all symptoms may not apply depending on the configuration of Rook. If the majority of the symptoms are seen there is a fair chance you are experiencing that problem.

If after trying the suggestions found on this page and the problem is not resolved, the Rook team is very happy to help you troubleshoot the issues in their Slack channel. Once you have [registered for the Rook Slack](https://slack.rook.io), proceed to the `#ceph` channel to ask for assistance.

## Table of Contents <!-- omit in toc -->

* [Troubleshooting Techniques](#troubleshooting-techniques)
* [Pod Using Ceph Storage Is Not Running](#pod-using-ceph-storage-is-not-running)
* [Cluster failing to service requests](#cluster-failing-to-service-requests)
* [Monitors are the only pods running](#monitors-are-the-only-pods-running)
* [PVCs stay in pending state](#pvcs-stay-in-pending-state)
* [OSD pods are failing to start](#osd-pods-are-failing-to-start)
* [OSD pods are not created on my devices](#osd-pods-are-not-created-on-my-devices)
* [Node hangs after reboot](#node-hangs-after-reboot)
* [Rook Agent modprobe exec format error](#rook-agent-modprobe-exec-format-error)
* [Rook Agent rbd module missing error](#rook-agent-rbd-module-missing-error)
* [Using multiple shared filesystem (CephFS) is attempted on a kernel version older than 4.7](#using-multiple-shared-filesystem-cephfs-is-attempted-on-a-kernel-version-older-than-47)
* [Set debug log level for all Ceph daemons](#set-debug-log-level-for-all-ceph-daemons)
* [Activate log to file for a particular Ceph daemon](#activate-log-to-file-for-a-particular-ceph-daemon)
* [A worker node using RBD devices hangs up](#a-worker-node-using-rbd-devices-hangs-up)
* [Too few PGs per OSD warning is shown](#too-few-pgs-per-osd-warning-is-shown)
* [LVM metadata can be corrupted with OSD on LV-backed PVC](#lvm-metadata-can-be-corrupted-with-osd-on-lv-backed-pvc)
* [OSD prepare job fails due to low aio-max-nr setting](#osd-prepare-job-fails-due-to-low-aio-max-nr-setting)
* [Failed to create CRDs](#failed-to-create-crds)
* [Unexpected partitions created](#unexpected-partitions-created)

See also the [CSI Troubleshooting Guide](ceph-csi-troubleshooting.md).

## Troubleshooting Techniques

There are two main categories of information you will need to investigate issues in the cluster:

1. Kubernetes status and logs documented [here](common-issues.md)
1. Ceph cluster status (see upcoming [Ceph tools](#ceph-tools) section)

### Ceph Tools

After you verify the basic health of the running pods, next you will want to run Ceph tools for status of the storage components. There are two ways to run the Ceph tools, either in the Rook toolbox or inside other Rook pods that are already running.

* Logs on a specific node to find why a PVC is failing to mount:
  * Rook agent errors around the attach/detach: `kubectl logs -n rook-ceph <rook-ceph-agent-pod>`
* See the [log collection topic](ceph-advanced-configuration.md#log-collection) for a script that will help you gather the logs
* Other artifacts:
  * The monitors that are expected to be in quorum: `kubectl -n <cluster-namespace> get configmap rook-ceph-mon-endpoints -o yaml | grep data`

#### Tools in the Rook Toolbox

The [rook-ceph-tools pod](./ceph-toolbox.md) provides a simple environment to run Ceph tools. Once the pod is up and running, connect to the pod to execute Ceph commands to evaluate that current state of the cluster.

```console
kubectl -n rook-ceph exec -it $(kubectl -n rook-ceph get pod -l "app=rook-ceph-tools" -o jsonpath='{.items[0].metadata.name}') bash
```

#### Ceph Commands

Here are some common commands to troubleshoot a Ceph cluster:

* `ceph status`
* `ceph osd status`
* `ceph osd df`
* `ceph osd utilization`
* `ceph osd pool stats`
* `ceph osd tree`
* `ceph pg stat`

The first two status commands provide the overall cluster health. The normal state for cluster operations is HEALTH_OK, but will still function when the state is in a HEALTH_WARN state. If you are in a WARN state, then the cluster is in a condition that it may enter the HEALTH_ERROR state at which point *all* disk I/O operations are halted. If a HEALTH_WARN state is observed, then one should take action to prevent the cluster from halting when it enters the HEALTH_ERROR state.

There are many Ceph sub-commands to look at and manipulate Ceph objects, well beyond the scope this document. See the [Ceph documentation](https://docs.ceph.com/) for more details of gathering information about the health of the cluster. In addition, there are other helpful hints and some best practices located in the [Advanced Configuration section](advanced-configuration.md). Of particular note, there are scripts for collecting logs and gathering OSD information there.

## Pod Using Ceph Storage Is Not Running

> This topic is specific to creating PVCs based on Rook's **Flex** driver, which is no longer the default option.
> By default, Rook deploys the CSI driver for binding the PVCs to the storage.

### Symptoms

* The pod that is configured to use Rook storage is stuck in the `ContainerCreating` status
* `kubectl describe pod` for the pod mentions one or more of the following:
  * `PersistentVolumeClaim is not bound`
  * `timeout expired waiting for volumes to attach/mount`
* `kubectl -n rook-ceph get pod` shows the rook-ceph-agent pods in a `CrashLoopBackOff` status

If you see that the PVC remains in **pending** state, see the topic [PVCs stay in pending state](#pvcs-stay-in-pending-state).

### Possible Solutions Summary

* `rook-ceph-agent` pod is in a `CrashLoopBackOff` status because it cannot deploy its driver on a read-only filesystem: [Flexvolume configuration pre-reqs](./ceph-prerequisites.md#ceph-flexvolume-configuration)
* Persistent Volume and/or Claim are failing to be created and bound: [Volume Creation](#volume-creation)
* `rook-ceph-agent` pod is failing to mount and format the volume: [Rook Agent Mounting](#volume-mounting)

### Investigation Details

If you see some of the symptoms above, it's because the requested Rook storage for your pod is not being created and mounted successfully.
In this walkthrough, we will be looking at the wordpress mysql example pod that is failing to start.

To first confirm there is an issue, you can run commands similar to the following and you should see similar output (note that some of it has been omitted for brevity):

```console
kubectl get pod
```

>```
>NAME                              READY     STATUS              RESTARTS   AGE
>wordpress-mysql-918363043-50pjr   0/1       ContainerCreating   0          1h
>```

```console
$ kubectl describe pod wordpress-mysql-918363043-50pjr
```

>```
>...
>Events:
>  FirstSeen	LastSeen	Count	From			SubObjectPath	Type		Reason			Message
>  ---------	--------	-----	----			-------------	--------	------			-------
>  1h		1h		3	default-scheduler			Warning		FailedScheduling	PersistentVolumeClaim is not bound: "mysql-pv-claim" (repeated 2 times)
>  1h		35s		36	kubelet, 172.17.8.101			Warning		FailedMount		Unable to mount volumes for pod "wordpress-mysql-918363043-50pjr_default(08d14e75-bd99-11e7-bc4c-001c428b9fc8)": timeout expired waiting for volumes to attach/mount for pod "default"/"wordpress-mysql-918363043-50pjr". list of unattached/unmounted volumes=[mysql-persistent-storage]
>  1h		35s		36	kubelet, 172.17.8.101			Warning		FailedSync		Error syncing pod
>```

To troubleshoot this, let's walk through the volume provisioning steps in order to confirm where the failure is happening.

#### Ceph Agent Deployment

The `rook-ceph-agent` pods are responsible for mapping and mounting the volume from the cluster onto the node that your pod will be running on.
If the `rook-ceph-agent` pod is not running then it cannot perform this function.

Below is an example of the `rook-ceph-agent` pods failing to get to the `Running` status because they are in a `CrashLoopBackOff` status:

```console
kubectl -n rook-ceph get pod
```

>```
>NAME                                  READY     STATUS             RESTARTS   AGE
>rook-ceph-agent-ct5pj                 0/1       CrashLoopBackOff   16         59m
>rook-ceph-agent-zb6n9                 0/1       CrashLoopBackOff   16         59m
>rook-operator-2203999069-pmhzn        1/1       Running            0          59m
>```

If you see this occurring, you can get more details about why the `rook-ceph-agent` pods are continuing to crash with the following command and its sample output:

```console
kubectl -n rook-ceph get pod -l app=rook-ceph-agent -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.containerStatuses[0].lastState.terminated.message}{"\n"}{end}'
```
>```
>rook-ceph-agent-ct5pj	mkdir /usr/libexec/kubernetes: read-only filesystem
>rook-ceph-agent-zb6n9	mkdir /usr/libexec/kubernetes: read-only filesystem
>```

From the output above, we can see that the agents were not able to bind mount to `/usr/libexec/kubernetes` on the host they are scheduled to run on.
For some environments, this default path is read-only and therefore a better path must be provided to the agents.

First, clean up the agent deployment with:

```console
kubectl -n rook-ceph delete daemonset rook-ceph-agent
```

Once the `rook-ceph-agent` pods are gone, **follow the instructions in the [Flexvolume configuration pre-reqs](./ceph-prerequisites.md#ceph-flexvolume-configuration)** to ensure a good value for `--volume-plugin-dir` has been provided to the Kubelet.
After that has been configured, and the Kubelet has been restarted, start the agent pods up again by restarting `rook-operator`:

```console
kubectl -n rook-ceph delete pod -l app=rook-ceph-operator
```

#### Volume Creation

The volume must first be created in the Rook cluster and then bound to a volume claim before it can be mounted to a pod.
Let's confirm that with the following commands and their output:

```console
kubectl get pv
```

>```
>NAME                                       CAPACITY   ACCESSMODES   RECLAIMPOLICY   STATUS     CLAIM                    STORAGECLASS   REASON    AGE
>pvc-9f273fbc-bdbf-11e7-bc4c-001c428b9fc8   20Gi       RWO           Delete          Bound      default/mysql-pv-claim   rook-ceph-block               25m
>```

```console
kubectl get pvc
```

>```
>NAME             STATUS    VOLUME                                     CAPACITY   ACCESSMODES   STORAGECLASS   AGE
>mysql-pv-claim   Bound     pvc-9f273fbc-bdbf-11e7-bc4c-001c428b9fc8   20Gi       RWO           rook-ceph-block     25m
>```

Both your volume and its claim should be in the `Bound` status.
If one or neither of them is not in the `Bound` status, then look for details of the issue in the `rook-operator` logs:

```console
kubectl -n rook-ceph logs `kubectl -n rook-ceph -l app=rook-ceph-operator get pods -o jsonpath='{.items[*].metadata.name}'`
```

If the volume is failing to be created, there should be details in the `rook-operator` log output, especially those tagged with `op-provisioner`.

One common cause for the `rook-operator` failing to create the volume is when the `clusterNamespace` field of the `StorageClass` doesn't match the **namespace** of the Rook cluster, as described in [#1502](https://github.com/rook/rook/issues/1502).
In that scenario, the `rook-operator` log would show a failure similar to the following:

>```
>2018-03-28 18:58:32.041603 I | op-provisioner: creating volume with configuration {pool:replicapool clusterNamespace:rook-ceph fstype:}
>2018-03-28 18:58:32.041728 I | exec: Running command: rbd create replicapool/pvc-fd8aba49-32b9-11e8-978e-08002762c796 --size 20480 --cluster=rook --conf=/var/lib/rook/rook-ceph/rook.config --keyring=/var/lib/rook/rook-ceph/client.admin.keyring
>E0328 18:58:32.060893       5 controller.go:801] Failed to provision volume for claim "default/mysql-pv-claim" with StorageClass "rook-ceph-block": Failed to create rook block image replicapool/pvc-fd8aba49-32b9-11e8-978e-08002762c796: failed to create image pvc-fd8aba49-32b9-11e8-978e-08002762c796 in pool replicapool of size 21474836480: Failed to complete '': exit status 1. global_init: unable to open config file from search list /var/lib/rook/rook-ceph/rook.config
>. output:
>```

The solution is to ensure that the [`clusterNamespace`](https://github.com/rook/rook/blob/master/cluster/examples/kubernetes/ceph/flex/storageclass.yaml#L28) field matches the **namespace** of the Rook cluster when creating the `StorageClass`.

#### Volume Mounting

The final step in preparing Rook storage for your pod is for the `rook-ceph-agent` pod to mount and format it.
If all the preceding sections have been successful or inconclusive, then take a look at the `rook-ceph-agent` pod logs for further clues.
You can determine which `rook-ceph-agent` is running on the same node that your pod is scheduled on by using the `-o wide` output, then you can get the logs for that `rook-ceph-agent` pod similar to the example below:

```console
kubectl -n rook-ceph get pod -o wide
```

>```
>NAME                                  READY     STATUS    RESTARTS   AGE       IP             NODE
>rook-ceph-agent-h6scx                 1/1       Running   0          9m        172.17.8.102   172.17.8.102
>rook-ceph-agent-mp7tn                 1/1       Running   0          9m        172.17.8.101   172.17.8.101
>rook-operator-2203999069-3tb68        1/1       Running   0          9m        10.32.0.7      172.17.8.101
>```

```console
$ kubectl -n rook-ceph logs rook-ceph-agent-h6scx
```

>```
>2017-10-30 23:07:06.984108 I | rook: starting Rook v0.5.0-241.g48ce6de.dirty with arguments '/usr/local/bin/rook agent'
>[...]
>```

In the `rook-ceph-agent` pod logs, you may see a snippet similar to the following:

>```
>Failed to complete rbd: signal: interrupt.
>```

In this case, the agent waited for the `rbd` command but it did not finish in a timely manner so the agent gave up and stopped it.
This can happen for multiple reasons, but using `dmesg` will likely give you insight into the root cause.
If `dmesg` shows something similar to below, then it means you have an old kernel that can't talk to the cluster:

>```
>libceph: mon2 10.205.92.13:6789 feature set mismatch, my 4a042a42 < server's 2004a042a42, missing 20000000000
>```

If `uname -a` shows that you have a kernel version older than `3.15`, you'll need to perform **one** of the following:

* Disable some Ceph features by starting the [rook toolbox](./ceph-toolbox.md) and running `ceph osd crush tunables bobtail`
* Upgrade your kernel to `3.15` or later.

#### Filesystem Mounting

In the `rook-ceph-agent` pod logs, you may see a snippet similar to the following:

>```
>2017-11-07 00:04:37.808870 I | rook-flexdriver: WARNING: The node kernel version is 4.4.0-87-generic, which do not support multiple ceph filesystems. The kernel version has to be at least 4.7. If you have multiple ceph filesystems, the result could be inconsistent
>```

This will happen in kernels with versions older than 4.7, where the option `mds_namespace` is not supported. This option is used to specify a filesystem namespace.

In this case, if there is only one filesystem in the Rook cluster, there should be no issues and the mount should succeed. If you have more than one filesystem, inconsistent results may arise and the filesystem mounted may not be the one you specified.

If the issue is still not resolved from the steps above, please come chat with us on the **#general** channel of our [Rook Slack](https://slack.rook.io).
We want to help you get your storage working and learn from those lessons to prevent users in the future from seeing the same issue.

## Cluster failing to service requests

### Symptoms

* Execution of the `ceph` command hangs
* PersistentVolumes are not being created
* Large amount of slow requests are blocking
* Large amount of stuck requests are blocking
* One or more MONs are restarting periodically

### Investigation

Create a [rook-ceph-tools pod](ceph-toolbox.md) to investigate the current state of Ceph. Here is an example of what one might see. In this case the `ceph status` command would just hang so a CTRL-C needed to be sent.

```console
kubectl -n rook-ceph exec -it deploy/rook-ceph-tools -- ceph status

ceph status
^CCluster connection interrupted or timed out
```

Another indication is when one or more of the MON pods restart frequently. Note the 'mon107' that has only been up for 16 minutes in the following output.

```console
kubectl -n rook-ceph get all -o wide --show-all
```

>```
>NAME                                 READY     STATUS    RESTARTS   AGE       IP               NODE
>po/rook-ceph-mgr0-2487684371-gzlbq   1/1       Running   0          17h       192.168.224.46   k8-host-0402
>po/rook-ceph-mon107-p74rj            1/1       Running   0          16m       192.168.224.28   k8-host-0402
>rook-ceph-mon1-56fgm                 1/1       Running   0          2d        192.168.91.135   k8-host-0404
>rook-ceph-mon2-rlxcd                 1/1       Running   0          2d        192.168.123.33   k8-host-0403
>rook-ceph-osd-bg2vj                  1/1       Running   0          2d        192.168.91.177   k8-host-0404
>rook-ceph-osd-mwxdm                  1/1       Running   0          2d        192.168.123.31   k8-host-0403
>```

### Solution

What is happening here is that the MON pods are restarting and one or more of the Ceph daemons are not getting configured with the proper cluster information. This is commonly the result of not specifying a value for `dataDirHostPath` in your Cluster CRD.

The `dataDirHostPath` setting specifies a path on the local host for the Ceph daemons to store configuration and data. Setting this to a path like `/var/lib/rook`, reapplying your Cluster CRD and restarting all the Ceph daemons (MON, MGR, OSD, RGW) should solve this problem. After the Ceph daemons have been restarted, it is advisable to restart the [rook-tool pod](./toolbox.md).

## Monitors are the only pods running

### Symptoms

* Rook operator is running
* Either a single mon starts or the mons start very slowly (at least several minutes apart)
* The crash-collector pods are crashing
* No mgr, osd, or other daemons are created except the CSI driver

### Investigation

When the operator is starting a cluster, the operator will start one mon at a time and check that they are healthy before continuing to bring up all three mons.
If the first mon is not detected healthy, the operator will continue to check until it is healthy. If the first mon fails to start, a second and then a third
mon may attempt to start. However, they will never form quorum and the orchestration will be blocked from proceeding.

The crash-collector pods will be blocked from starting until the mons have formed quorum the first time.

There are several common causes for the mons failing to form quorum:

* The operator pod does not have network connectivity to the mon pod(s). The network may be configured incorrectly.
* One or more mon pods are in running state, but the operator log shows they are not able to form quorum
* A mon is using configuration from a previous installation. See the [cleanup guide](ceph-teardown.md#delete-the-data-on-hosts)
  for cleaning the previous cluster.
* A firewall may be blocking the ports required for the Ceph mons to form quorum. Ensure ports 6789 and 3300 are enabled.
  See the [Ceph networking guide](https://docs.ceph.com/en/latest/rados/configuration/network-config-ref/) for more details.

#### Operator fails to connect to the mon

First look at the logs of the operator to confirm if it is able to connect to the mons.

```console
kubectl -n rook-ceph logs -l app=rook-ceph-operator
```

Likely you will see an error similar to the following that the operator is timing out when connecting to the mon. The last command is `ceph mon_status`,
followed by a timeout message five minutes later.

>```
>2018-01-21 21:47:32.375833 I | exec: Running command: ceph mon_status --cluster=rook --conf=/var/lib/rook/rook-ceph/rook.config --keyring=/var/lib/rook/rook-ceph/client.admin.keyring --format json --out-file /tmp/442263890
>2018-01-21 21:52:35.370533 I | exec: 2018-01-21 21:52:35.071462 7f96a3b82700  0 monclient(hunting): authenticate timed out after 300
>2018-01-21 21:52:35.071462 7f96a3b82700  0 monclient(hunting): authenticate timed out after 300
>2018-01-21 21:52:35.071524 7f96a3b82700  0 librados: client.admin authentication error (110) Connection timed out
>2018-01-21 21:52:35.071524 7f96a3b82700  0 librados: client.admin authentication error (110) Connection timed out
>[errno 110] error connecting to the cluster
>```

The error would appear to be an authentication error, but it is misleading. The real issue is a timeout.

#### Solution

If you see the timeout in the operator log, verify if the mon pod is running (see the next section).
If the mon pod is running, check the network connectivity between the operator pod and the mon pod.
A common issue is that the CNI is not configured correctly.

To verify the network connectivity:
- Get the endpoint for a mon
- Curl the mon from the operator pod

For example, this command will curl the first mon from the operator:

```
kubectl -n rook-ceph exec deploy/rook-ceph-operator -- curl $(kubectl -n rook-ceph get svc -l app=rook-ceph-mon -o jsonpath='{.items[0].spec.clusterIP}'):3300 2>/dev/null
```

>```
>ceph v2
>```

If "ceph v2" is printed to the console, the connection was successful. If the command does not respond or
otherwise fails, the network connection cannot be established.

#### Failing mon pod

Second we need to verify if the mon pod started successfully.

```console
kubectl -n rook-ceph get pod -l app=rook-ceph-mon
```

>```
>NAME                                READY     STATUS               RESTARTS   AGE
>rook-ceph-mon-a-69fb9c78cd-58szd    1/1       CrashLoopBackOff     2          47s
>```

If the mon pod is failing as in this example, you will need to look at the mon pod status or logs to determine the cause. If the pod is in a crash loop backoff state,
you should see the reason by describing the pod.

```console
# The pod shows a termination status that the keyring does not match the existing keyring
kubectl -n rook-ceph describe pod -l mon=rook-ceph-mon0
```

>```
>...
>    Last State:    Terminated
>      Reason:    Error
>      Message:    The keyring does not match the existing keyring in /var/lib/rook/rook-ceph-mon0/data/keyring.
>                    You may need to delete the contents of dataDirHostPath on the host from a previous deployment.
>...
>```

See the solution in the next section regarding cleaning up the `dataDirHostPath` on the nodes.

#### Solution

This is a common problem reinitializing the Rook cluster when the local directory used for persistence has **not** been purged.
This directory is the `dataDirHostPath` setting in the cluster CRD and is typically set to `/var/lib/rook`.
To fix the issue you will need to delete all components of Rook and then delete the contents of `/var/lib/rook` (or the directory specified by `dataDirHostPath`) on each of the hosts in the cluster.
Then when the cluster CRD is applied to start a new cluster, the rook-operator should start all the pods as expected.

> **IMPORTANT: Deleting the `dataDirHostPath` folder is destructive to the storage. Only delete the folder if you are trying to permanently purge the Rook cluster.**

See the [Cleanup Guide](ceph-teardown.md) for more details.

## PVCs stay in pending state

### Symptoms

* When you create a PVC based on a rook storage class, it stays pending indefinitely

For the Wordpress example, you might see two PVCs in pending state.

```console
kubectl get pvc
```

>```
>NAME             STATUS    VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS      AGE
>mysql-pv-claim   Pending                                      rook-ceph-block   8s
>wp-pv-claim      Pending                                      rook-ceph-block   16s
>```

### Investigation

There are two common causes for the PVCs staying in pending state:

1. There are no OSDs in the cluster
2. The CSI provisioner pod is not running or is not responding to the request to provision the storage

If you are still using the Rook flex driver for the volumes (the CSI driver is the default since Rook v1.1),
another cause could be that the operator is not running or is otherwise not responding to the request to provision the storage.

#### Confirm if there are OSDs

To confirm if you have OSDs in your cluster, connect to the [Rook Toolbox](ceph-toolbox.md) and run the `ceph status` command.
You should see that you have at least one OSD `up` and `in`. The minimum number of OSDs required depends on the
`replicated.size` setting in the pool created for the storage class. In a "test" cluster, only one OSD is required
(see `storageclass-test.yaml`). In the production storage class example (`storageclass.yaml`), three OSDs would be required.

```console
ceph status
```

>```
>  cluster:
>    id:     a0452c76-30d9-4c1a-a948-5d8405f19a7c
>    health: HEALTH_OK
>
>  services:
>    mon: 3 daemons, quorum a,b,c (age 11m)
>    mgr: a(active, since 10m)
>    osd: 1 osds: 1 up (since 46s), 1 in (since 109m)
>```

#### OSD Prepare Logs

If you don't see the expected number of OSDs, let's investigate why they weren't created.
On each node where Rook looks for OSDs to configure, you will see an "osd prepare" pod.

```console
kubectl -n rook-ceph get pod -l app=rook-ceph-osd-prepare
```

>```
>NAME                                 ...  READY   STATUS      RESTARTS   AGE
>rook-ceph-osd-prepare-minikube-9twvk   0/2     Completed   0          30m
>```

See the section on [why OSDs are not getting created](#osd-pods-are-not-created-on-my-devices) to investigate the logs.

#### CSI Driver

The CSI driver may not be responding to the requests. Look in the logs of the CSI provisioner pod to see if there are any errors
during the provisioning.

There are two provisioner pods:

```
kubectl -n rook-ceph get pod -l app=csi-rbdplugin-provisioner
```

Get the logs of each of the pods. One of them should be the "leader" and be responding to requests.

```
kubectl -n rook-ceph logs csi-cephfsplugin-provisioner-d77bb49c6-q9hwq csi-provisioner
```

See also the [CSI Troubleshooting Guide](ceph-csi-troubleshooting.md).


#### Operator unresponsiveness

Lastly, if you have OSDs `up` and `in`, the next step is to confirm the operator is responding to the requests.
Look in the Operator pod logs around the time when the PVC was created to confirm if the request is being raised.
If the operator does not show requests to provision the block image, the operator may be stuck on some other operation.
In this case, restart the operator pod to get things going again.

### Solution

If the "osd prepare" logs didn't give you enough clues about why the OSDs were not being created,
please review your [cluster.yaml](eph-cluster-crd.html#storage-selection-settings) configuration.
The common misconfigurations include:

* If `useAllDevices: true`, Rook expects to find local devices attached to the nodes. If no devices are found, no OSDs will be created.
* If `useAllDevices: false`, OSDs will only be created if `deviceFilter` is specified.
* Only local devices attached to the nodes will be configurable by Rook. In other words, the devices must show up under `/dev`.
  * The devices must not have any partitions or filesystems on them. Rook will only configure raw devices. Partitions are not yet supported.

## OSD pods are failing to start

### Symptoms

* OSD pods are failing to start
* You have started a cluster after tearing down another cluster

### Investigation

When an OSD starts, the device or directory will be configured for consumption. If there is an error with the configuration, the pod will crash and you will see the CrashLoopBackoff
status for the pod. Look in the osd pod logs for an indication of the failure.

```console
$ kubectl -n rook-ceph logs rook-ceph-osd-fl8fs
...
```

One common case for failure is that you have re-deployed a test cluster and some state may remain from a previous deployment.
If your cluster is larger than a few nodes, you may get lucky enough that the monitors were able to start and form quorum. However, now the OSDs pods may fail to start due to the
old state. Looking at the OSD pod logs you will see an error about the file already existing.

```console
$ kubectl -n rook-ceph logs rook-ceph-osd-fl8fs
```

>```
>...
>2017-10-31 20:13:11.187106 I | mkfs-osd0: 2017-10-31 20:13:11.186992 7f0059d62e00 -1 bluestore(/var/lib/rook/osd0) _read_fsid unparsable uuid
>2017-10-31 20:13:11.187208 I | mkfs-osd0: 2017-10-31 20:13:11.187026 7f0059d62e00 -1 bluestore(/var/lib/rook/osd0) _setup_block_symlink_or_file failed to create block symlink to /dev/disk/by-partuuid/651153ba-2dfc-4231-ba06-94759e5ba273: (17) File exists
>2017-10-31 20:13:11.187233 I | mkfs-osd0: 2017-10-31 20:13:11.187038 7f0059d62e00 -1 bluestore(/var/lib/rook/osd0) mkfs failed, (17) File exists
>2017-10-31 20:13:11.187254 I | mkfs-osd0: 2017-10-31 20:13:11.187042 7f0059d62e00 -1 OSD::mkfs: ObjectStore::mkfs failed with error (17) File exists
>2017-10-31 20:13:11.187275 I | mkfs-osd0: 2017-10-31 20:13:11.187121 7f0059d62e00 -1  ** ERROR: error creating empty object store in /var/lib/rook/osd0: (17) File exists
>```

### Solution

If the error is from the file that already exists, this is a common problem reinitializing the Rook cluster when the local directory used for persistence has **not** been purged.
This directory is the `dataDirHostPath` setting in the cluster CRD and is typically set to `/var/lib/rook`.
To fix the issue you will need to delete all components of Rook and then delete the contents of `/var/lib/rook` (or the directory specified by `dataDirHostPath`) on each of the hosts in the cluster.
Then when the cluster CRD is applied to start a new cluster, the rook-operator should start all the pods as expected.

## OSD pods are not created on my devices

### Symptoms

* No OSD pods are started in the cluster
* Devices are not configured with OSDs even though specified in the Cluster CRD
* One OSD pod is started on each node instead of multiple pods for each device

### Investigation

First, ensure that you have specified the devices correctly in the CRD.
The [Cluster CRD](ceph-cluster-crd.md#storage-selection-settings) has several ways to specify the devices that are to be consumed by the Rook storage:

* `useAllDevices: true`: Rook will consume all devices it determines to be available
* `deviceFilter`: Consume all devices that match this regular expression
* `devices`: Explicit list of device names on each node to consume

Second, if Rook determines that a device is not available (has existing partitions or a formatted filesystem), Rook will skip consuming the devices.
If Rook is not starting OSDs on the devices you expect, Rook may have skipped it for this reason. To see if a device was skipped, view the OSD preparation log
on the node where the device was skipped. Note that it is completely normal and expected for OSD prepare pod to be in the `completed` state.
After the job is complete, Rook leaves the pod around in case the logs need to be investigated.

```console
# Get the prepare pods in the cluster
kubectl -n rook-ceph get pod -l app=rook-ceph-osd-prepare
```

>```
>NAME                                   READY     STATUS      RESTARTS   AGE
>rook-ceph-osd-prepare-node1-fvmrp      0/1       Completed   0          18m
>rook-ceph-osd-prepare-node2-w9xv9      0/1       Completed   0          22m
>rook-ceph-osd-prepare-node3-7rgnv      0/1       Completed   0          22m
>```

```console
# view the logs for the node of interest in the "provision" container
kubectl -n rook-ceph logs rook-ceph-osd-prepare-node1-fvmrp provision
[...]
```

Here are some key lines to look for in the log:

>```
># A device will be skipped if Rook sees it has partitions or a filesystem
>2019-05-30 19:02:57.353171 W | cephosd: skipping device sda that is in use
>2019-05-30 19:02:57.452168 W | skipping device "sdb5": ["Used by ceph-disk"]
>
># Other messages about a disk being unusable by ceph include:
>Insufficient space (<5GB) on vgs
>Insufficient space (<5GB)
>LVM detected
>Has BlueStore device label
>locked
>read-only
>
># A device is going to be configured
>2019-05-30 19:02:57.535598 I | cephosd: device sdc to be configured by ceph-volume
>
># For each device configured you will see a report printed to the log
>2019-05-30 19:02:59.844642 I |   Type            Path                                                    LV Size         % of device
>2019-05-30 19:02:59.844651 I | ----------------------------------------------------------------------------------------------------
>2019-05-30 19:02:59.844677 I |   [data]          /dev/sdc                                                7.00 GB         100%
>```

### Solution

Either update the CR with the correct settings, or clean the partitions or filesystem from your devices.
To clean devices from a previous install see the [cleanup guide](ceph-teardown.md#zapping-devices).

After the settings are updated or the devices are cleaned, trigger the operator to analyze the devices again by restarting the operator.
Each time the operator starts, it will ensure all the desired devices are configured. The operator does automatically
deploy OSDs in most scenarios, but an operator restart will cover any scenarios that the operator doesn't detect automatically.

```console
# Restart the operator to ensure devices are configured. A new pod will automatically be started when the current operator pod is deleted.
kubectl -n rook-ceph delete pod -l app=rook-ceph-operator
[...]
```

## Node hangs after reboot

This issue is fixed in Rook v1.3 or later.

### Symptoms

* After issuing a `reboot` command, node never returned online
* Only a power cycle helps

### Investigation

On a node running a pod with a Ceph persistent volume

```console
mount | grep rbd
```
>```
># _netdev mount option is absent, also occurs for cephfs
># OS is not aware PV is mounted over network
>/dev/rbdx on ... (rw,relatime, ..., noquota)
>```

When the reboot command is issued, network interfaces are terminated before disks
are unmounted. This results in the node hanging as repeated attempts to unmount
Ceph persistent volumes fail with the following error:

>```
>libceph: connect [monitor-ip]:6789 error -101
>```

### Solution

The node needs to be [drained](https://kubernetes.io/docs/tasks/administer-cluster/safely-drain-node/) before reboot. After the successful drain, the node can be rebooted as usual.

Because `kubectl drain` command automatically marks the node as unschedulable (`kubectl cordon` effect), the node needs to be uncordoned once it's back online.

Drain the node:

```console
$ kubectl drain <node-name> --ignore-daemonsets --delete-local-data
```

Uncordon the node:

```console
$ kubectl uncordon <node-name>
```

## Rook Agent modprobe exec format error

### Symptoms

* PersistentVolumes from Ceph fail/timeout to mount
* Rook Agent logs contain `modinfo: ERROR: could not get modinfo from 'rbd': Exec format error` lines

### Solution

If it is feasible to upgrade your kernel, you should upgrade to `4.x`, even better is >= `4.7` due to a feature for CephFS added to the kernel.

If you are unable to upgrade the kernel, you need to go to each host that will consume storage and run:

```console
modprobe rbd
```

This command inserts the `rbd` module into the kernel.

To persist this fix, you need to add the `rbd` kernel module to either `/etc/modprobe.d/` or `/etc/modules-load.d/`.
For both paths create a file called `rbd.conf` with the following content:

```console
rbd
```

Now when a host is restarted, the module should be loaded automatically.

## Rook Agent rbd module missing error

### Symptoms

* Rook Agent in `Error` or `CrashLoopBackOff` status when deploying the Rook operator with `kubectl create -f operator.yaml`:

```console
kubectl -n rook-ceph get pod
```

>```
>NAME                                 READY     STATUS    RESTARTS   AGE
>rook-ceph-agent-gfrm5                0/1       Error     0          14s
>rook-ceph-operator-5f4866946-vmtff   1/1       Running   0          23s
>rook-discover-qhx6c                  1/1       Running   0          14s
>```

* Rook Agent logs contain below messages:

>```
>2018-08-10 09:09:09.461798 I | exec: Running command: cat /lib/modules/4.15.2/modules.builtin
>2018-08-10 09:09:09.473858 I | exec: Running command: modinfo -F parm rbd
>2018-08-10 09:09:09.477215 N | ceph-volumeattacher: failed rbd single_major check, assuming it's unsupported: failed to check for rbd module single_major param: Failed to complete 'check kmod param': exit status 1. modinfo: ERROR: Module rbd not found.
>2018-08-10 09:09:09.477239 I | exec: Running command: modprobe rbd
>2018-08-10 09:09:09.480353 I | modprobe rbd: modprobe: FATAL: Module rbd not found.
>2018-08-10 09:09:09.480452 N | ceph-volumeattacher: failed to load kernel module rbd: failed to load kernel module rbd: Failed to complete 'modprobe rbd': exit status 1.
>failed to run rook ceph agent. failed to create volume manager: failed to load >kernel module rbd: Failed to complete 'modprobe rbd': exit status 1.
>```

### Solution

From the log message of Agent, we can see that the `rbd` kernel module is not available in the current system, neither as a builtin nor a loadable external kernel module.

In this case, you have to [re-configure and build](https://www.linuxjournal.com/article/6568) a new kernel to address this issue, there're two options:

* Re-configure your kernel to make sure the `CONFIG_BLK_DEV_RBD=y` in the `.config` file, then build the kernel.
* Re-configure your kernel to make sure the `CONFIG_BLK_DEV_RBD=m` in the `.config` file, then build the kernel.

Rebooting the system to use the new kernel, this issue should be fixed: the Agent will be in normal `running` status if everything was done correctly.

## Using multiple shared filesystem (CephFS) is attempted on a kernel version older than 4.7

### Symptoms

* More than one shared filesystem (CephFS) has been created in the cluster
* A pod attempts to mount any other shared filesystem besides the **first** one that was created
* The pod incorrectly gets the first filesystem mounted instead of the intended filesystem

### Solution

The only solution to this problem is to upgrade your kernel to `4.7` or higher.
This is due to a mount flag added in the kernel version `4.7` which allows to chose the filesystem by name.

For additional info on the kernel version requirement for multiple shared filesystems (CephFS), see [Filesystem - Kernel version requirement](ceph-filesystem.md#kernel-version-requirement).

## Set debug log level for all Ceph daemons

You can set a given log level and apply it to all the Ceph daemons at the same time.
For this, make sure the toolbox pod is running, then determine the level you want (between 0 and 20).
You can find the list of all subsystems and their default values in [Ceph logging and debug official guide](https://docs.ceph.com/en/latest/rados/troubleshooting/log-and-debug/#ceph-subsystems). Be careful when increasing the level as it will produce very verbose logs.

Assuming you want a log level of 1, you will run:

```console
kubectl -n rook-ceph exec deploy/rook-ceph-tools -- set-ceph-debug-level 1
```

Output:

>```quote
> ceph config set global debug_context 1
> ceph config set global debug_lockdep 1
>...
>...
>```

Once you are done debugging, you can revert all the debug flag to their default value by running the following:

```console
kubectl -n rook-ceph exec deploy/rook-ceph-tools -- set-ceph-debug-level default
```

## Activate log to file for a particular Ceph daemon

They are cases where looking at Kubernetes logs is not enough for diverse reasons, but just to name a few:

* not everyone is familiar for Kubernetes logging and expects to find logs in traditional directories
* logs get eaten (buffer limit from the log engine) and thus not requestable from Kubernetes

So for each daemon, `dataDirHostPath` is used to store logs, if logging is activated.
Rook will bindmount `dataDirHostPath` for every pod.
Let's say you want to enable logging for `mon.a`, but only for this daemon.
Using the toolbox or from inside the operator run:

```console
ceph config set mon.a log_to_file true
```

This will activate logging on the filesystem, you will be able to find logs in `dataDirHostPath/$NAMESPACE/log`, so typically this would mean `/var/lib/rook/rook-ceph/log`.
You don't need to restart the pod, the effect will be immediate.

To disable the logging on file, simply set `log_to_file` to `false`.

## A worker node using RBD devices hangs up

### Symptoms

* There is no progress on I/O from/to one of RBD devices (`/dev/rbd*` or `/dev/nbd*`).
* After that, the whole worker node hangs up.

### Investigation

This happens when the following conditions are satisfied.

- The problematic RBD device and the corresponding OSDs are co-located.
- There is an XFS filesystem on top of this device.

In addition, when this problem happens, you can see the following messages in `dmesg`.

```console
dmesg
```
>```
>...
>[51717.039319] INFO: task kworker/2:1:5938 blocked for more than 120 seconds.
>[51717.039361]       Not tainted 4.15.0-72-generic #81-Ubuntu
>[51717.039388] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>...
>```

It's so-called `hung_task` problem and means that there is a deadlock in the kernel. For more detail, please refer to [the corresponding issue comment](https://github.com/rook/rook/issues/3132#issuecomment-580508760).

### Solution

This problem will be solve by the following two fixes.

* Linux kernel: A minor feature that is introduced by [this commit](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8d19f1c8e1937baf74e1962aae9f90fa3aeab463). It will be included in Linux v5.6.
* Ceph: A fix that uses the above-mentioned kernel's feature. The Ceph community will probably discuss this fix after releasing Linux v5.6.

You can bypass this problem by using ext4 or any other filesystems rather than XFS. Filesystem type can be specified with `csi.storage.k8s.io/fstype` in StorageClass resource.

## Too few PGs per OSD warning is shown

### Symptoms

- `ceph status` shows "too few PGs per OSD" warning as follows.

```console
ceph status
```

>```
>  cluster:
>    id:     fd06d7c3-5c5c-45ca-bdea-1cf26b783065
>    health: HEALTH_WARN
>            too few PGs per OSD (16 < min 30)
>```

### Solution

The meaning of this warning is written in [the document](https://docs.ceph.com/docs/master/rados/operations/health-checks#too-few-pgs).
However, in many cases it is benign. For more information, please see [the blog entry](http://ceph.com/community/new-luminous-pg-overdose-protection/).
Please refer to [Configuring Pools](ceph-advanced-configuration.md#configuring-pools) if you want to know the proper `pg_num` of pools and change these values.

## LVM metadata can be corrupted with OSD on LV-backed PVC

### Symptoms

There is a critical flaw in OSD on LV-backed PVC. LVM metadata can be corrupted if both the host and OSD container modify it simultaneously. For example, the administrator might modify it on the host, while the OSD initialization process in a container could modify it too. In addition, if `lvmetad` is running, the possibility of occurrence gets higher. In this case, the change of LVM metadata in OSD container is not reflected to LVM metadata cache in host for a while.

If you still decide to configure an OSD on LVM, please keep the following in mind to reduce the probability of this issue.

### Solution

- Disable `lvmetad.`
- Avoid configuration of LVs from the host. In addition, don't touch the VGs and physical volumes that back these LVs.
- Avoid incrementing the `count` field of `storageClassDeviceSets` and create a new LV that backs an OSD simultaneously.

You can know whether the above-mentioned tag exists with the command: `sudo lvs -o lv_name,lv_tags`. If the `lv_tag` field is empty in an LV corresponding to the OSD lv_tags, this OSD encountered the problem. In this case, please [retire this OSD](ceph-osd-mgmt.md#remove-an-osd) or replace with other new OSD before restarting.

This problem doesn't happen in newly created LV-backed PVCs because OSD container doesn't modify LVM metadata anymore. The existing lvm mode OSDs work continuously even thought upgrade your Rook. However, using the raw mode OSDs is recommended because of the above-mentioned problem. You can replace the existing OSDs with raw mode OSDs by retiring them and adding new OSDs one by one. See the documents [Remove an OSD](ceph-osd-mgmt.md#remove-an-osd) and [Add an OSD on a PVC](ceph-osd-mgmt.md#add-an-osd-on-a-pvc).

## OSD prepare job fails due to low aio-max-nr setting

If the Kernel is configured with a low [aio-max-nr setting](https://www.kernel.org/doc/Documentation/sysctl/fs.txt), the OSD prepare job might fail with the following error:

```text
exec: stderr: 2020-09-17T00:30:12.145+0000 7f0c17632f40 -1 bdev(0x56212de88700 /var/lib/ceph/osd/ceph-0//block) _aio_start io_setup(2) failed with EAGAIN; try increasing /proc/sys/fs/aio-max-nr
```

To overcome this, you need to increase the value of `fs.aio-max-nr` of your sysctl configuration (typically `/etc/sysctl.conf`).
You can do this with your favorite configuration management system.

Alternatively, you can have a [DaemonSet](https://github.com/rook/rook/issues/6279#issuecomment-694390514) to apply the configuration for you on all your nodes.

## Failed to create CRDs
If you are using Kubernetes version is v1.15 or older, you will see an error like this:
>```
>unable to recognize "STDIN": no matches for kind "CustomResourceDefinition" in version "apiextensions.k8s.io/v1"
>```
You need to create the CRDs found in `cluster/examples/kubernetes/ceph/pre-k8s-1.16`. Note that these pre-1.16 `apiextensions.k8s.io/v1beta1` CRDs are deprecated in k8s v1.16 and will no longer be supported from k8s v1.22.


## Unexpected partitions created

### Symptoms
**Users running Rook versions v1.6.0-v1.6.7 may observe unwanted OSDs on partitions that appear
unexpectedly and seemingly randomly, which can corrupt existing OSDs.**

Unexpected partitions are created on host disks that are used by Ceph OSDs. This happens more often
on SSDs than HDDs and usually only on disks that are 875GB or larger. Many tools like `lsblk`,
`blkid`, `udevadm`, and `parted` will not show a partition table type for the partition. Newer
versions of `blkid` are generally able to recognize the type as "atari".

The underlying issue causing this is Atari partition (sometimes identified as AHDI) support in the
Linux kernel. Atari partitions have very relaxed specifications compared to other partition types,
and it is relatively easy for random data written to a disk to appear as an Atari partition to the
Linux kernel. Ceph's Bluestore OSDs have an anecdotally high probability of writing data on to disks
that can appear to the kernel as an Atari partition.

Below is an example of `lsblk` output from a node where phantom Atari partitions are present. Note
that `sdX1` is never present for the phantom partitions, and `sdX2` is 48G on all disks. `sdX3`
is a variable size and may not always be present. It is possible for `sdX4` to appear, though it is
an anecdotally rare event.
```
# lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sdb      8:16   0     3T  0 disk
├─sdb2   8:18   0    48G  0 part
└─sdb3   8:19   0   6.1M  0 part
sdc      8:32   0     3T  0 disk
├─sdc2   8:34   0    48G  0 part
└─sdc3   8:35   0   6.2M  0 part
sdd      8:48   0     3T  0 disk
├─sdd2   8:50   0    48G  0 part
└─sdd3   8:51   0   6.3M  0 part
```

You can see https://github.com/rook/rook/issues/7940 for more detailed information and discussion.

### Solution
#### Recover from corruption (v1.6.0-v1.6.7)
If you are using Rook v1.6, you must first update to v1.6.8 or higher to avoid further incidents of
OSD corruption caused by these Atari partitions.

An old workaround suggested using `deviceFilter: ^sd[a-z]+$`, but this still results in unexpected
partitions. Rook will merely stop creating new OSDs on the partitions. It does not fix a related
issue that `ceph-volume` that is unaware of the Atari partition problem. Users who used this
workaround are still at risk for OSD failures in the future.

To resolve the issue, immediately update to v1.6.8 or higher. After the update, no corruption should
occur on OSDs created in the future. Next, to get back to a healthy Ceph cluster state, focus on one
corruped disk at a time and [remove all OSDs on each corrupted disk](ceph-osd-mgmt.md#remove-an-osd)
one disk at a time.

As an example, you may have `/dev/sdb` with two unexpected partitions (`/dev/sdb2` and `/dev/sdb3`)
as well as a second corrupted disk `/dev/sde` with one unexpected partition (`/dev/sde2`).
1. First, remove the OSDs associated with `/dev/sdb`, `/dev/sdb2`, and `/dev/sdb3`. There might be
   only one, or up to 3 OSDs depending on how your system was affected. Again see the
   [OSD management doc](ceph-osd-mgmt.md#remove-an-osd).
2. Use `dd` to wipe the first sectors of the partitions followed by the disk itself. E.g.,
   - `dd if=/dev/zero of=/dev/sdb2 bs=1M`
   - `dd if=/dev/zero of=/dev/sdb3 bs=1M`
   - `dd if=/dev/zero of=/dev/sdb bs=1M`
3. Then wipe clean `/dev/sdb` to prepare it for a new OSD.
   See [the teardown document](ceph-teardown.md#zapping-devices) for details.
4. After this, scale up the Rook operator to deploy a new OSD to `/dev/sdb`. This will allow Ceph to
   use `/dev/sdb` for data recovery and replication while the next OSDs are removed.
5. Now Repeat steps 1-4 for `/dev/sde` and `/dev/sde2`, and continue for any other corruped disks.

If your Rook-Ceph cluster does not have any critical data stored in it, it may be simpler to
uninstall Rook completely and redeploy with v1.6.8 or higher.
