# Rules

Rules are defined using a logical language.

The GUI provides a simple way of creating rules.

Creating more complicated rules which may include maths calculations
and MySQL queries can be done using [macros](Macros.md)

## Syntax

Rules must consist of at least 3 elements: An __Entity__, a __Condition__ and a __Value__.
Rules can contain braces and __Glues__.

__Entities__ are provided from Table and Field from the database. For Example: `ports.ifOperStatus`.

__Conditions__ can be any of:

- Equals `=`
- Not Equals `!=`
- In `IN`
- Not In `NOT IN`
- Begins with `LIKE ('...%')`
- Doesn't begin with `NOT LIKE ('...%')`
- Contains `LIKE ('%...%')`
- Doesn't Contain `NOT LIKE ('%...%')`
- Ends with `LIKE ('%...')`
- Doesn't end with `NOT LIKE ('%...')`
- Between `BETWEEN`
- Not Between `NOT BETWEEN`
- Is Empty `= ''`
- Is Not Empty `!= '''`
- Is Null `IS NULL`
- Is Not Null `IS NOT NULL`
- Greater `>`
- Greater or Equal `>=`
- Less `<`
- Less or Equal `<=`
- Regex `REGEXP`

__Values__ can be an entity or any data. If using macros or another column name as a value you
must include the macro or column name with backticks. i.e. \`macros.past_60m\` or \`processors.processor_perc_warn\`.

__Note__: Regex supports MySQL Regular expressions.

Arithmetics are allowed as well.

## Options

Here are some of the other options available when adding an alerting rule:

- Rule name: The name associated with the rule.
- Severity: How "important" the rule is.
- Max alerts: The maximum number of alerts sent for the event.  `-1` means unlimited.
- Delay: The amount of time in seconds to wait after a rule is matched
  before sending an alert out transport.
- Interval: The interval of time in seconds between alerts for an
  event until Max alert is reached.
- Mute alerts: Disables sending alert rule through alert
  transport. But will still show the alert in the Web UI.
- Invert match: Invert the matching rule (ie. alert on items that
  _don't match the rule).
- Recovery alerts: This will disable the recovery notification from
  being sent if turned off.

## Advanced

On the Advanced tab, you can specify some additional options for the alert rule:

- Override SQL: Enable this if you using a custom query
- Query: The query to be used for the alert.

- An example of this would be an average rule for all CPUs over 10%

```sql
SELECT devices.*,AVG(processors.processor_usage) AS cpu_avg, processors.* FROM 
devices INNER JOIN processors ON devices.device_id 
= processors.device_id WHERE devices.device_id 
= ? AND devices.status = 1 AND devices.disabled = 
0 AND devices.ignore = 0 GROUP BY devices.device_id, 
devices.status, devices.disabled, devices.ignore 
HAVING AVG(processors.processor_usage) 
> 10;
```

!!! note
    The 10 would then contain the average CPU usage value, you can
    change this value to be whatever you like.
    You will to need copy and paste this into the Alert Rule under
    Advanced then paste into Query box and switch the Override SQL.

## Procedure

You can provide procedure URL when creating the rule. Only links
like "http://" are supported, otherwise an error will be returned.
Once configured, procedures can be opened from the Alert widget
through the "Open" button, which can be shown/hidden from the
widget configuration box.

## Examples

Alert when:

- Device goes down: `devices.status != 1`
- Any port changes: `ports.ifOperStatus != 'up'`
- Root-directory gets too full: `storage.storage_descr = '/' AND
  storage.storage_perc >= '75'`
- Any storage gets fuller than the 'warning': `storage.storage_perc >= storage_perc_warn`
- If device is a server and the used storage is above the warning
  level, but ignore /boot partitions: `storage.storage_perc >
  storage.storage_perc_warn AND devices.type = "server" AND
  storage.storage_descr != "/boot"`
- VMware LAG is not using "Source ip address hash" load balancing:
  `devices.os = "vmware" AND ports.ifType = "ieee8023adLag" AND
  ports.ifDescr REGEXP "Link Aggregation .*, load balancing algorithm:
  Source ip address hash"`
- Syslog, authentication failure during the last 5m:
  `syslog.timestamp >= macros.past_5m AND syslog.msg REGEXP ".*authentication failure.*"`
- High memory usage: `macros.device_up = 1 AND mempools.mempool_perc >=
 90 AND mempools.mempool_descr REGEXP "Virtual.*"`
- High CPU usage(per core usage, not overall): `macros.device_up
  = 1 AND processors.processor_usage >= 90`
- High port usage, where description is not client & ifType is not
  softwareLoopback: `macros.port_usage_perc >= 80 AND
  port.port_descr_type != "client" AND ports.ifType != "softwareLoopback"`
- Alert when mac address is located on your network `ipv4_mac.mac_address = "2c233a756912"`
- Device MTU test fails: `devices.mtu_status != 1`

## Alert Rules Collection

You can also select Alert Rule from the Alerts Collection. These Alert
Rules are submitted by users in the community :) If would like to
submit your alert rules to the collection, please submit them here [Alert Rules Collection](https://github.com/librenms/librenms/edit/master/resources/definitions/alert_rules.json)

![Alert Rules Collection](../img/alert-rules-collection.png)
