Notice

This document is for a development version of Ceph.

Troubleshooting

This section explains how to investigate why a cephadm command failed or why a certain service no longer runs properly.

Cephadm deploys daemons within containers. Troubleshooting containerized daemons requires a different process than does troubleshooting traditional daemons that were installed by means of packages.

Here are some tools and commands to help you troubleshoot your Ceph environment.

Pausing or Disabling cephadm

If something goes wrong and cephadm is behaving badly, pause most of the Ceph cluster’s background activity by running the following command:

ceph orch pause

This stops all changes in the Ceph cluster, but cephadm will still periodically check hosts to refresh its inventory of daemons and devices. Disable cephadm completely by running the following commands:

ceph orch set backend ''
ceph mgr module disable cephadm

These commands disable all of the ceph orch ... CLI commands. All previously deployed daemon containers continue to run and will start just as they were before you ran these commands.

See Disabling automatic deployment of daemons for more on disabling individual services.

Per-service and Per-daemon Events

To make it easier to debug failed daemons, cephadm stores events per service and per daemon. These events often contain information relevant to the troubleshooting of your Ceph cluster.

Listing Service Events

To see the events associated with a certain service, run a command of the following form:

ceph orch ls --service_name=<service-name> --format yaml

This will return something in the following form:

service_type: alertmanager
service_name: alertmanager
placement:
  hosts:
  - unknown_host
status:
  ...
  running: 1
  size: 1
events:
- 2021-02-01T08:58:02.741162 service:alertmanager [INFO] "service was created"
- '2021-02-01T12:09:25.264584 service:alertmanager [ERROR] "Failed to apply: Cannot
  place <AlertManagerSpec for service_name=alertmanager> on unknown_host: Unknown hosts"'

Listing Daemon Events

To see the events associated with a certain daemon, run a command of the following form:

ceph orch ps --service-name <service-name> --daemon-id <daemon-id> --format yaml

This will return something in the following form:

daemon_type: mds
daemon_id: cephfs.hostname.ppdhsz
hostname: hostname
status_desc: running
...
events:
- 2021-02-01T08:59:43.845866 daemon:mds.cephfs.hostname.ppdhsz [INFO] "Reconfigured
  mds.cephfs.hostname.ppdhsz on host 'hostname'"

Checking Cephadm Logs

To learn how to monitor cephadm logs as they are generated, read Watching cephadm log messages.

If your Ceph cluster has been configured to log events to files, there will be a ceph.cephadm.log file on all monitor hosts. See Ceph daemon control for a more complete explanation.

Gathering Log Files

Use journalctl to gather the log files of all daemons:

Note

By default cephadm now stores logs in journald. This means that you will no longer find daemon logs in /var/log/ceph/.

To read the log file of one specific daemon, run a command of the following form:

cephadm logs --name <name-of-daemon>

Note

This works only when run on the same host that is running the daemon. To get the logs of a daemon that is running on a different host, add the --fsid option to the command, as in the following example:

cephadm logs --fsid <fsid> --name <name-of-daemon>

In this example, <fsid> corresponds to the cluster ID returned by the ceph status command.

To fetch all log files of all daemons on a given host, run the following for-loop:

for name in $(cephadm ls | jq -r '.[].name') ; do
  cephadm logs --fsid <fsid> --name "$name" > $name;
done

Collecting Systemd Status

To print the state of a systemd unit, run a command of the following form:

systemctl status "ceph-$(cephadm shell ceph fsid)@<service name>.service";

To fetch the state of all daemons of a given host, run the following shell script:

fsid="$(cephadm shell ceph fsid)"
for name in $(cephadm ls | jq -r '.[].name') ; do
  systemctl status "ceph-$fsid@$name.service" > $name;
done

List all Downloaded Container Images

To list all container images that are downloaded on a host, run the following commands:

podman ps -a --format json | jq '.[].Image' "docker.io/library/centos:8" "registry.opensuse.org/opensuse/leap:15.2"

Note

Image might also be called ImageID.

Manually Running Containers

Cephadm uses small wrappers when running containers. Refer to /var/lib/ceph/<cluster-fsid>/<service-name>/unit.run for the container execution command.

SSH Errors

Error message:

execnet.gateway_bootstrap.HostNotFound: -F /tmp/cephadm-conf-73z09u6g -i /tmp/cephadm-identity-ky7ahp_5 root@10.10.1.2
...
raise OrchestratorError(msg) from e
orchestrator._interface.OrchestratorError: Failed to connect to 10.10.1.2 (10.10.1.2).
Please make sure that the host is reachable and accepts connections using the cephadm SSH key
...

If you receive the above error message, try the following things to troubleshoot the SSH connection between cephadm and the monitor:

  1. Ensure that cephadm has an SSH identity key:

    [root@mon1~]# cephadm shell -- ceph config-key get mgr/cephadm/ssh_identity_key > ~/cephadm_private_key
    INFO:cephadm:Inferring fsid f8edc08a-7f17-11ea-8707-000c2915dd98
    INFO:cephadm:Using recent ceph image docker.io/ceph/ceph:v15 obtained 'mgr/cephadm/ssh_identity_key'
    [root@mon1 ~] # chmod 0600 ~/cephadm_private_key
    

If this fails, cephadm doesn’t have a key. Fix this by running the following command:

[root@mon1 ~]# cephadm shell -- ceph cephadm generate-ssh-key

or:

[root@mon1 ~]# cat ~/cephadm_private_key | cephadm shell -- ceph cephadm set-ssh-key -i -
  1. Ensure that the SSH config is correct:

    [root@mon1 ~]# cephadm shell -- ceph cephadm get-ssh-config > config
    
  2. Verify that it is possible to connect to the host:

    [root@mon1 ~]# ssh -F config -i ~/cephadm_private_key root@mon1
    

Verifying that the Public Key is Listed in the authorized_keys file

To verify that the public key is in the authorized_keys file, run the following commands:

[root@mon1 ~]# cephadm shell -- ceph cephadm get-pub-key > ~/ceph.pub
[root@mon1 ~]# grep "`cat ~/ceph.pub`"  /root/.ssh/authorized_keys

Failed to Infer CIDR network error

If you see this error:

ERROR: Failed to infer CIDR network for mon ip ***; pass --skip-mon-network to configure it later

Or this error:

Must set public_network config option or specify a CIDR network, ceph addrvec, or plain IP

This means that you must run a command of this form:

ceph config set mon public_network <mon_network>

For more detail on operations of this kind, see Deploying additional monitors.

Accessing the Admin Socket

Each Ceph daemon provides an admin socket that bypasses the MONs (See Using the Admin Socket).

  1. To access the admin socket, enter the daemon container on the host:

    [root@mon1 ~]# cephadm enter --name <daemon-name>
    
  2. Run a command of the following form to see the admin socket’s configuration:

    [ceph: root@mon1 /]# ceph --admin-daemon /var/run/ceph/ceph-<daemon-name>.asok config show
    

Running Various Ceph Tools

To run Ceph tools such as ceph-objectstore-tool or ceph-monstore-tool, invoke the cephadm CLI with cephadm shell --name <daemon-name>. For example:

root@myhostname # cephadm unit --name mon.myhostname stop
root@myhostname # cephadm shell --name mon.myhostname
[ceph: root@myhostname /]# ceph-monstore-tool /var/lib/ceph/mon/ceph-myhostname get monmap > monmap
[ceph: root@myhostname /]# monmaptool --print monmap
monmaptool: monmap file monmap
epoch 1
fsid 28596f44-3b56-11ec-9034-482ae35a5fbb
last_changed 2021-11-01T20:57:19.755111+0000
created 2021-11-01T20:57:19.755111+0000
min_mon_release 17 (quincy)
election_strategy: 1
0: [v2:127.0.0.1:3300/0,v1:127.0.0.1:6789/0] mon.myhostname

The cephadm shell sets up the environment in a way that is suitable for extended daemon maintenance and for the interactive running of daemons.

Restoring the Monitor Quorum

If the Ceph Monitor daemons (mons) cannot form a quorum, cephadm will not be able to manage the cluster until quorum is restored.

In order to restore the quorum, remove unhealthy monitors form the monmap by following these steps:

  1. Stop all Monitors. Use ssh to connect to each Monitor’s host, and then while connected to the Monitor’s host use cephadm to stop the Monitor daemon:

    ssh {mon-host}
    cephadm unit --name {mon.hostname} stop
    
  2. Identify a surviving Monitor and log in to its host:

    ssh {mon-host}
    cephadm enter --name {mon.hostname}
    
  3. Follow the steps in Removing Monitors from an Unhealthy Cluster.

Manually Deploying a Manager Daemon

At least one Manager (mgr) daemon is required by cephadm in order to manage the cluster. If the last remaining Manager has been removed from the Ceph cluster, follow these steps in order to deploy a fresh Manager on an arbitrary host in your cluster. In this example, the freshly-deployed Manager daemon is called mgr.hostname.smfvfd.

  1. Disable the cephadm scheduler, in order to prevent cephadm from removing the new Manager. See Enable Ceph CLI:

    ceph config-key set mgr/cephadm/pause true
    
  2. Retrieve or create the “auth entry” for the new Manager:

    ceph auth get-or-create mgr.hostname.smfvfd mon "profile mgr" osd "allow *" mds "allow *"
    
  3. Retrieve the Monitor’s configuration:

    ceph config generate-minimal-conf
    
  4. Retrieve the container image:

    ceph config get "mgr.hostname.smfvfd" container_image
    
  5. Create a file called config-json.json, which contains the information necessary to deploy the daemon:

    {
      "config": "# minimal ceph.conf for 8255263a-a97e-4934-822c-00bfe029b28f\n[global]\n\tfsid = 8255263a-a97e-4934-822c-00bfe029b28f\n\tmon_host = [v2:192.168.0.1:40483/0,v1:192.168.0.1:40484/0]\n",
      "keyring": "[mgr.hostname.smfvfd]\n\tkey = V2VyIGRhcyBsaWVzdCBpc3QgZG9vZi4=\n"
    }
    
  6. Deploy the Manager daemon:

    cephadm --image <container-image> deploy --fsid <fsid> --name mgr.hostname.smfvfd --config-json config-json.json
    

Capturing Core Dumps

A Ceph cluster that uses cephadm can be configured to capture core dumps. The initial capture and processing of the coredump is performed by systemd-coredump.

To enable coredump handling, run the following command

ulimit -c unlimited

Note

Core dumps are not namespaced by the kernel. This means that core dumps are written to /var/lib/systemd/coredump on the container host. The ulimit -c unlimited setting will persist only until the system is rebooted.

Wait for the crash to happen again. To simulate the crash of a daemon, run for example killall -3 ceph-mon.

Running the Debugger with cephadm

Running a single debugging session

Initiate a debugging session by using the cephadm shell command. From within the shell container we need to install the debugger and debuginfo packages. To debug a core file captured by systemd, run the following:

  1. Start the shell session:

    cephadm shell --mount /var/lib/system/coredump
    
  2. From within the shell session, run the following commands:

    dnf install ceph-debuginfo gdb zstd
    
    unzstd /var/lib/systemd/coredump/core.ceph-*.zst
    
    gdb /usr/bin/ceph-mon /mnt/coredump/core.ceph-*.zst
    
  3. Run debugger commands at gdb’s prompt:

    bt
    
    #0  0x00007fa9117383fc in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
    #1  0x00007fa910d7f8f0 in std::condition_variable::wait(std::unique_lock<std::mutex>&) () from /lib64/libstdc++.so.6
    #2  0x00007fa913d3f48f in AsyncMessenger::wait() () from /usr/lib64/ceph/libceph-common.so.2
    #3  0x0000563085ca3d7e in main ()
    

Running repeated debugging sessions

When using cephadm shell, as in the example above, any changes made to the container that is spawned by the shell command are ephemeral. After the shell session exits, the files that were downloaded and installed cease to be available. You can simply re-run the same commands every time cephadm shell is invoked, but to save time and resources you can create a new container image and use it for repeated debugging sessions.

In the following example, we create a simple file that constructs the container image. The command below uses podman but it is expected to work correctly even if podman is replaced with docker:

cat >Containerfile <<EOF
ARG BASE_IMG=quay.io/ceph/ceph:v18
FROM \${BASE_IMG}
# install ceph debuginfo packages, gdb and other potentially useful packages
RUN dnf install --enablerepo='*debug*' -y ceph-debuginfo gdb zstd strace python3-debuginfo
EOF
podman build -t ceph:debugging -f Containerfile .
# pass --build-arg=BASE_IMG=<your image> to customize the base image

The above file creates a new local image named ceph:debugging. This image can be used on the same machine that built it. The image can also be pushed to a container repository or saved and copied to a node that is running other Ceph containers. See the podman or docker documentation for more information about the container workflow.

After the image has been built, it can be used to initiate repeat debugging sessions. By using an image in this way, you avoid the trouble of having to re-install the debug tools and the debuginfo packages every time you need to run a debug session. To debug a core file using this image, in the same way as previously described, run:

cephadm --image ceph:debugging shell --mount /var/lib/system/coredump

Debugging live processes

The gdb debugger can attach to running processes to debug them. This can be achieved with a containerized process by using the debug image and attaching it to the same PID namespace in which the process to be debugged resides.

This requires running a container command with some custom arguments. We can generate a script that can debug a process in a running container.

cephadm --image ceph:debugging shell --dry-run > /tmp/debug.sh

This creates a script that includes the container command that cephadm would use to create a shell. Modify the script by removing the --init argument and replace it with the argument that joins to the namespace used for a running running container. For example, assume we want to debug the Manager and have determnined that the Manager is running in a container named ceph-bc615290-685b-11ee-84a6-525400220000-mgr-ceph0-sluwsk. In this case, the argument --pid=container:ceph-bc615290-685b-11ee-84a6-525400220000-mgr-ceph0-sluwsk should be used.

We can run our debugging container with sh /tmp/debug.sh. Within the shell, we can run commands such as ps to get the PID of the Manager process. In the following example this is 2. While running gdb, we can attach to the running process:

attach 2
info threads
bt

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