OpenSnitch is a GNU/Linux port of the Little Snitch application firewall.

TL;DR

Make sure you have a correctly configured Go >= 1.8 environment, that the $GOPATH environment variable is defined and then:

# install dependencies
sudo apt-get install protobuf-compiler libpcap-dev libnetfilter-queue-dev
go get github.com/golang/protobuf/protoc-gen-go
go get -u github.com/golang/dep/cmd/dep
# clone the repository (ignore the message about no Go files being found)
go get github.com/evilsocket/opensnitch
cd $GOPATH/src/github.com/evilsocket/opensnitch
# compile && install
make
sudo make install
# enable opensnitchd as a systemd service and start the UI
sudo systemctl enable opensnitchd
sudo service opensnitchd start
opensnitch-ui

Daemon

The daemon is implemented in Go and needs to run as root in order to interact with the Netfilter packet queue, edit iptables rules and so on, in order to compile it you will need to install the protobuf-compiler, libpcap-dev and libnetfilter-queue-dev packages on your system, then just:

cd daemon
make

You can then install it as a systemd service by doing:

sudo make install

The new opensnitchd service will log to /var/log/opensnitchd.log, save the rules inside /etc/opensnitchd/rules and connect to the default UI service socket unix:///tmp/osui.sock.

UI

The user interface is a Python 3 software running as a gRPC server on a unix socket, to order to install its dependencies:

cd ui
sudo pip3 install -r requirements.txt

You will also need to install the package python-pyqt5 for your system (if anyone finds a way to make this work from the requirements.txt file feel free to send a PR).

The UI is pip installable itself:

sudo pip3 install .

This will install the opensnitch-ui command on your system (you can auto startup it by cp opensnitch_ui.desktop ~/.config/autostart/).

UI Configuration

By default the UI will load its configuration from ~/.opensnitch/ui-config.json (customizable with the --config argument), the default contents of this file are:

{
	"default_timeout": 15,
	"default_action": "allow",
	"default_duration": "until restart"
}

The default_timeout is the number of seconds after which the UI will take its default action, the default_action can be allow or deny and the default_duration, which indicates for how long the default action should be taken, can be once, until restart or always to persist the action as a new rule on disk.

Running

Once you installed both the daemon and the UI, you can enable the opensnitchd service to run at boot time:

sudo systemctl enable opensnitchd

And run it with:

sudo service opensnitchd start

While the UI can be started just by executing the opensnitch-ui command.

Single UI with many computers

You can also use --socket "[::]:50051" to have the UI use TCP instead of a unix socket and run the daemon on another computer with -ui-socket "x.x.x.x:50051" (where x.x.x.x is the IP of the computer running the UI service).

Rules

Rules are stored as JSON files inside the -rule-path folder, in the simplest cast 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,
   "action": "deny",
   "duration": "always",
   "operator": {
     "type": "simple",
     "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.
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 == comparision 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.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, dest.ip, dest.host or dest.port.
operator.data	The data to compare the operand to, can be a regular expression if type is regexp.

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,
   "action": "deny",
   "duration": "always",
   "operator": {
     "type": "regexp",
     "operand": "dest.host",
     "data": "(?i).*analytics.*\\.google\\.com"
   }
}

An example whitelisting a whole process:

{
   "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,
   "action": "allow",
   "duration": "always",
   "operator": {
     "type": "simple",
     "operand": "process.path",
     "data": "/opt/google/chrome/chrome"
   }
 }

FAQ

Why Qt and not GTK?

I tried, but for very fast updates it failed bad on my configuration (failed bad = SIGSEGV), moreover I find Qt5 layout system superior and easier to use.

Why gRPC and not DBUS?

The UI service is able to use a TCP listener instead of a UNIX socket, that means the UI service itself can be executed on any operating system, while receiving messages from a single local daemon instance or multiple instances from remote computers in the network, therefore DBUS would have made the protocol and logic uselessly GNU/Linux specific.