Rules

Rules format

Rules are stored as JSON files inside the -rule-path folder, in the simplest case a rule looks like this:

{
   "created": "2018-04-07T14:13:27.903996051+02:00",
   "updated": "2018-04-07T14:13:27.904060088+02:00",
   "name": "deny-simple-www-google-analytics-l-google-com",
   "enabled": true,
   "precedence": false,
   "action": "deny",
   "duration": "always",
   "operator": {
     "type": "simple",
     "sensitive": false,
     "operand": "dest.host",
     "data": "www-google-analytics.l.google.com"
   }
}

Field	Description
created	UTC date and time of creation.
update	UTC date and time of the last update.
name	The name of the rule.
enabled	Use to temporarily disable and enable rules without moving their files.
precedence	true or false. Sets if a rule take precedence (>= v1.2.0)
action	Can be deny or allow.
duration	For rules persisting on disk, this value is default to always.
operator.type	Can be simple, in which case a simple == comparison will be performed, or regexp if the data field is a regular expression to match.
operator.operand	What element of the connection to compare, can be one of:
	* true (will always match)
	* process.path (the path of the executable)
	*process.id PID
	*process.command (full command line, including path and arguments)
	*provess.env.ENV_VAR_NAME (use the value of an environment variable of the process given its name)
	*user.id (UID)
	*protocol
	*dest.ip
	*dest.host
	*dest.network (>= v1.3.0)
	* dest.port.
operator.data	The data to compare the operand to, can be a regular expression if type is regexp.

Some considerations

By default Deny rules take precedence over the rest of the rules. If a connection match a Deny rule, opensnitch won't continue evaluating rules.

Since v1.2.0, rules are sorted and checked in alphabetical order. You can name them this way to prioritize Deny rules, for example:

000-allow-very-important-rule
001-allow-not-so-important-rule
001-deny-xxx

Also since v1.2.0, you can configure a rule as Important ([x] Priority) to take precedence over the rest of the rules. If you set this flag and name the rule as mentoned above, you can also prioritize Allow rules.

This way you can not only prioritize critical connections (like VPNs), but also gain performance.

More on rules performance

As already mentioned, the order of the rule is critical. If you prioritize Firefox the web navegation will be faster.

But the type of rule also impacts the rules performance. regexp and list types are slower than simple, in the end, regexp and list types check multiple parameters while simple rules check just one.

---

An example with a regular expression:

{
   "created": "2018-04-07T14:13:27.903996051+02:00",
   "updated": "2018-04-07T14:13:27.904060088+02:00",
   "name": "deny-any-google-analytics",
   "enabled": true,
   "precedence": false,
   "action": "deny",
   "duration": "always",
   "operator": {
     "type": "regexp",
     "sensitive": false,
     "operand": "dest.host",
     "data": "(?i)
   }
}

An example whitelisting a process path:

{
   "created": "2018-04-07T15:00:48.156737519+02:00",
   "updated": "2018-04-07T15:00:48.156772601+02:00",
   "name": "allow-simple-opt-google-chrome-chrome",
   "enabled": true,
   "precedence": false,
   "action": "allow",
   "duration": "always",
   "operator": {
     "type": "simple",
     "sensitive": false,
     "operand": "process.path",
     "data": "/opt/google/chrome/chrome"
   }
 }

Example of a complex rule using the operator list, saved from the GUI (Note: version v1.2.0):

{
  "created": "2020-02-07T14:16:20.550255152+01:00",
  "updated": "2020-02-07T14:16:20.729849966+01:00",
  "name": "deny-list-type-simple-operand-destip-data-1101-type-simple-operand-destport-data-23-type-simple-operand-userid-data-1000-type-simple-operand-processpath-data-usrbintelnetnetkit",
  "enabled": true,
  "precedence": false,
  "action": "deny",
  "duration": "always",
  "operator": {
    "type": "list",
    "operand": "list",
    "data": "[{\"type\": \"simple\", \"operand\": \"dest.ip\", \"data\": \"1.1.0.1\"}, {\"type\": \"simple\", \"operand\": \"dest.port\", \"data\": \"23\"}, {\"type\": \"simple\", \"operand\": \"user.id\", \"data\": \"1000\"}, {\"type\": \"simple\", \"operand\": \"process.path\", \"data\": \"/usr/bin/telnet.netkit\"}]",
    "list": [
      {
        "type": "simple",
        "operand": "dest.ip",
        "sensitive": false,
        "data": "1.1.0.1",
        "list": null
      },
      {
        "type": "simple",
        "operand": "dest.port",
        "sensitive": false,
        "data": "23",
        "list": null
      },
      {
        "type": "simple",
        "operand": "user.id",
        "sensitive": false,
        "data": "1000",
        "list": null
      },
      {
        "type": "simple",
        "operand": "process.path",
        "sensitive": false,
        "data": "/usr/bin/telnet.netkit",
        "list": null
      }
    ]
  }
}