Troubleshooting

• Service logging
  • Log levels
  • Log file locations
• Permission issues
• Handlers and filters
• Assets not working properly

Service logging

Logs produced by Sensu services – i.e. sensu-backend and sensu-agent – are often the best place to start when troubleshooting a variety of issues.

Log levels

Each log message is associated with a log level, indicative of the relative severity of the event being logged:

These log levels can be configured by specifying the desired log level as the value of log-level in the service configuration file (e.g. agent.yml or backend.yml configuration files), or as an argument to the --log-level command line flag:

sensu-agent start --log-level debug

Changes to log level via configuration file or command line arguments require restarting the service. For guidance on restarting a service, please consult the Operating section of the agent or backend reference, respectively.

Log file locations

journalctl --follow --unit sensu-${service}

tail --follow /var/log/sensu/sensu-${service}

journalctl --follow --unit sensu-${service}

tail --follow /var/log/sensu/sensu-${service}

journalctl --follow --unit sensu-${service}

tail --follow /var/log/sensu/sensu-${service}

Get-Content -  Path "C:\scripts\test.txt" -Wait

Permission issues

Files and folders within /var/cache/sensu/ and /var/lib/sensu/ need to be owned by the sensu user and group. You will see a logged error similar to the following if there is a permission issue with either the sensu-backend or the sensu-agent:

{"component":"agent","error":"open /var/cache/sensu/sensu-agent/assets.db: permission denied","level":"fatal","msg":"error executing sensu-agent","time":"2019-02-21T22:01:04Z"}
{"component":"backend","level":"fatal","msg":"error starting etcd: mkdir /var/lib/sensu: permission denied","time":"2019-03-05T20:24:01Z"}

You can use a recursive chown to resolve permission issues with the sensu-backend:

sudo chown -R sensu:sensu /var/cache/sensu/sensu-backend

or the sensu-agent:

sudo chown -R sensu:sensu /var/cache/sensu/sensu-agent

Troubleshooting handlers and filters

Whether implementing new workflows or modifying existing ones, its sometimes necessary to troubleshoot various stages of the event pipeline. In many cases generating events using the agent API will save you time and effort over modifying existing check configurations.

Here’s an example using curl with the API of a local sensu-agent process to generate test-event check results:

curl -X POST \
-H 'Content-Type: application/json' \
-d '{
  "check": {
    "metadata": {
      "name": "test-event"
    },
    "status": 2,
    "output": "this is a test event targeting the email_ops handler",
    "handlers": [ "email_ops" ]
  }
}' \
http://127.0.0.1:3031/events

Additionally, it’s frequently helpful to see the full event object being passed to your workflows. We recommend using a debug handler like this one to write an event to disk as JSON data:

type: Handler
api_version: core/v2
metadata:
  name: debug
spec:
  type: pipe
  command: cat > /var/log/sensu/debug-event.json
  timeout: 2

{
  "type": "Handler",
  "api_version": "core/v2",
  "metadata": {
    "name": "debug"
  },
  "spec": {
    "type": "pipe",
    "command": "cat > /var/log/sensu/debug-event.json",
    "timeout": 2
  }
}

With this handler definition installed in your Sensu backend, you can add the debug to the list of handlers in your test event:

curl -X POST \
-H 'Content-Type: application/json' \
-d '{
  "check": {
    "metadata": {
      "name": "test-event"
    },
    "status": 2,
    "output": "this is a test event targeting the email_ops handler",
    "handlers": [ "email_ops", "debug" ]
  }
}' \
http://127.0.0.1:3031/events

The event data should be written to /var/log/sensu/debug-event.json for inspection. The contents of this file will be overwritten by every event sent to the debug handler.

NOTE: When multiple Sensu backends are configured in a cluster, event processing is distributed across all members. You may need to check the filesystem of each Sensu backend to locate the debug output for your test event.

Troubleshooting assets

Asset filters allow for scoping an asset to a particular operating system or architecture. You can see an example of those in the asset reference documentation. If an asset filter is improperly applied, this can prevent the asset from being downloaded by the desired entity and will result in error messages both on the agent and the backend illustrating that the command was not found:

Agent log entry

{
    "asset": "check-disk-space",
    "component": "asset-manager",
    "entity": "sensu-centos",
    "filters": [
        "true == false"
    ],
    "level": "debug",
    "msg": "entity not filtered, not installing asset",
    "time": "2019-09-12T18:28:05Z"
}

Backend event

 {
  "timestamp": 1568148292,
  "check": {
    "command": "check-disk-space",
    "handlers": [],
    "high_flap_threshold": 0,
    "interval": 10,
    "low_flap_threshold": 0,
    "publish": true,
    "runtime_assets": [
      "sensu-plugins-disk-checks"
    ],
    "subscriptions": [
      "caching_servers"
    ],
    "proxy_entity_name": "",
    "check_hooks": null,
    "stdin": false,
    "subdue": null,
    "ttl": 0,
    "timeout": 0,
    "round_robin": false,
    "duration": 0.001795508,
    "executed": 1568148292,
    "history": [
      {
        "status": 127,
        "executed": 1568148092
      }
    ],
    "issued": 1568148292,
    "output": "sh: check-disk-space: command not found\n",
    "state": "failing",
    "status": 127,
    "total_state_change": 0,
    "last_ok": 0,
    "occurrences": 645,
    "occurrences_watermark": 645,
    "output_metric_format": "",
    "output_metric_handlers": null,
    "env_vars": null,
    "metadata": {
      "name": "failing-disk-check",
      "namespace": "default"
    }
  },
  "metadata": {
    "namespace": "default"
  }
}

In the event you see a message like this, it’s worth going back and reviewing your asset definition as this will be your clue that the entity wasn’t able to download the required asset due to filter restrictions. If you can’t remember where you stored the information on disk, you can find it via:

sensuctl asset info sensu-plugins-disk-checks --format yaml

or

sensuctl asset info sensu-plugins-disk-checks --format json

One common filter issue is conflating operating systems with the family they’re a part of. For example, though Ubuntu is part of the Debian family of Linux distributions, Ubuntu != Debian. A practical example would look like:

...
    - entity.system.platform == 'debian'
    - entity.system.arch == 'amd64'

Which would not allow an Ubuntu system to run the asset. Instead, the filter should look like:

...
    - entity.system.platform_family == 'debian'
    - entity.system.arch == 'amd64'

or

    - entity.system.platform == 'ubuntu'
    - entity.system.arch == 'amd64'

Which would allow the asset to be downloaded onto the target entity.