Telnet usage

Flightgear comes with an internal telnet server. This so called "telnet" server provides a "remote shell" into the running FlightGear process. This can be used to read end set values within the Property Tree structure, but it can also be used for running fgcommands. The telnet server can be activated with the --telnet=port command line option, where port is the number of the listening port that will be opened.

A connection to the server can be done using a telnet client or opening a simple socket from any program. Multiple connection are possible at the same time.

Starting Flightgear with Telnet Server

For example, to start FG and open the port 5401 as available telnet server use this command:

fgfs --telnet=5401

Connect with Telnet Client

Once connected to the server using a telnet client, you will be given a prompt such as if you where connected to a unix telnet server, example:

francesco@francesco-desktop:~$ telnet 127.0.0.1 5401
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

Where 127.0.0.1 is the ip address of the running Flightgear server and 5401 is the port set when Flightgear started.

Now that you are inside a telnet session, you can start issuing commands (see below) to Flightgear. Generally commands are used to get, change and navigate the values of the property tree, similar to navigating with directories and files.

Prompt

Since we are simulating navigation through a file system, you will be given a prompt which consists of two parts:

1. current tree position
2. (the characters >(space))

so you will typically see something like the following:

/>
/autopilot[0]>
/autopilot[0]/settings[0]>

Commands

The following command are available:

• cd - change directory
• data - switch to data mode
• dump - dump to xml
• get - show a property value
• help - show available commands
• ls - list directories and paramaters
• prompt - switch to interactive mode
• pwd - display current path
• quit - terminate connection
• run - run a built in command
• set - set value of property
• ? - shortcut to help

cd

Change the current working directory; it needs a parameter which is the destination directory. Example session.

/> cd gear
/gear[0]>
/gear[0]> cd launchbar
/gear[0]/launchbar[0]> cd ..
/gear[0]> cd ..
/> cd gear/launchbar
/gear[0]/launchbar[0]> cd /
/>

data

Switch to data mode. This removes the prompt/>. This is mostly useful when communicating from code, eg a socket.

To switch back on see prompt below.

dump

dumps the current state in xml. This requires at least a directory argument.

/> dump postion/
-ERR "node 'postion/' not found"

/> dump /position 
<?xml version="1.0"?>
<PropertyList>
  <longitude-deg type="double">-122.3577761</longitude-deg>
  <latitude-deg type="double">37.61378776</latitude-deg>
  <altitude-ft type="double">28.25613943</altitude-ft>
  <ground-elev-m type="double">-0.131186098</ground-elev-m>
  <ground-elev-ft type="double">-0.4304005839</ground-elev-ft>
</PropertyList>

get

Shows the value of a given parameter, for example, to get the magnetos status inside the controls/engines/engine directory:

/> cd controls/engines/engine
/controls[0]/engines[0]/engine[0]>  get magnetos
magnetos = '3' (int)
/controls[0]/engines[0]/engine[0]> 

or from the root simply:

/> get controls/engines/engine/magnetos
controls/engines/engine/magnetos = '3' (int)
/>

help

Show all the available commands, same as just ?

ls

List all the directories and properties within and under the current directory, for example:

/> cd orientation
/orientation[0]> ls
heading-deg =	'70.62909768'	(double)
alpha-deg =	'-176.8560635'	(double)
pitch-rate-degps =	'3.347789774e-07'	(double)
/orientation[0]> 

or with a directory argument

/> ls /orientation
heading-deg =	'104.6032849'	(double)
alpha-deg =	'-176.864208'	(double)
pitch-rate-degps =	'-0.003761442232'	(double)
/>

prompt

Switch on interactive mode prompt/>. One by default. See data above to switch off.

pwd

Display the current directory ie print working directory

quit

Terminate the client connection to server.

run

Run a built in command, the command name is required as an argument.

set

Sets the value of a given property, for example, to set the aileron position inside the /controls/flight directory:

/> cd controls/flight
/controls[0]/flight[0]> set aileron 0.2
aileron = '0.2' (double)
/controls[0]/flight[0]> 

or simply:

/> set /controls/flight/aileron -0.1
/controls/flight/aileron = '-0.1' (double)
/>