Command line

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The command line is often mentioned as a tool for starting or setting up Flightgear, Atlas, Terrasync, FGCOM and other programs related to Flightgear. Many users simply don't know, what the command line acutally is or how to make use of it. This article shall help...

Windows XP

On Windows XP, you have access to the command line by clicking the "Start" button and then chosing "Run...". Type "cmd" (without quotation marks) into the field and hit Enter.

You should see the so called prompt now, which says something like that:


italic bold


Sublevel Caption


Or if it didn't work perfectly first time

   fgcom --help

returns the following useful info

   fgcom - a communication radio based on VoIP with IAX/Asterisk
   (c)2007 by H. Wirtz <>
   Version 1.2.2 build 163M
   Using iaxclient library Version SVN 163M
 OPTION                                        DESCRIPTION
 -d, -debug, --debug=                          show debugging information
 -S, -voipserver, --voipserver=                voip server to connect to (default: '')
 -s, -fgserver, --fgserver=                    fg to connect to  (default: 'localhost')
 -p, -port, --port=                            where we should listen to FG (default: '16661')
 -a, -airport, --airport=                      airport-id (ICAO) for ATC-mode
 -f, -frequency, --frequency=                  frequency for ATC-mode
 -U, -user, --user=                            username for VoIP account (default: 'guest')
 -P, -password, --password=                    password for VoIP account (default: 'guest')
 -i, -mic, --mic=                              mic input level (0.0 - 1.0)
 -o, -speaker, --speaker=                      speaker output level (0.0 - 1.0)
 -b, -mic-boost, --mic-boost=                  enable mic boost
 -l, -list-audio, --list-audio=                list audio devices
 -r, -set-audio-in, --set-audio-in=            use <devicename> as audio input
 -k, -set-audio-out, --set-audio-out=          use <devicename> as audio output
 -c, -codec, --codec=                          use codec <codec> as transfer codec (default: 'u')
 Available codecs:
       u - ulaw (default and best codec because the mixing is based onto ulaw)
       a - alaw
       g - gsm
       s - speex
       7 - G.723
 Mode 1: client for COM1 of flightgear:
       $ fgcom
 - connects fgcom to fgfs at localhost:16661
       $ fgcom -p23456
 - connects fgcom to fgfs at
 Mode 2: client for an ATC at <airport> on <frequency>:
       $ fgcom -aKSFO -f120.500
 - sets up fgcom for an ATC radio at KSFO 120.500 MHz
   Note that /home/hcs/src/fgcom/trunk/src/fgcom starts with a guest account unless you use -U and -P!

Also note that the current server ( works with guest account, so do not use -U or -P

Server installation

For running a FGCOM server you need Asterisk and depending on the amount of users much bandwith and CPU power. Because of putting pilots and ATCs in a VoIP conference the server-admin has to assure that there is enough network and cpu power to avoid drop-outs of the voice stream.


Install Asterisk on top of your favorite distribution. Please refer to installation manuals (e.g. [[1]]) you can find on the net. You do not need H.323 or SIP because the fgcom client uses IAX2 as VoIP signaling protocol. Only if you think about connecting external VoIP applications to FGCOM you should consider to activate H.323 or SIP (but this is not the scope of this small howto).

Notice: You need to install the zaptel driver modules - even if you won't use any hardware for telecom interfacing. You need the ztdummy kernel module for the asterisk conference application MeetMe() because it simulates a hardware clock needed by this application. Further development of FGCOM might use app_conference which don't needs any timing device.

For now we want to use /etc/asterisk as the base configuration directory.

Setting up the radio frequencies

The radio frequencies are "simple" Conferences and realized due to the Asterisk application MeetMe().

Part 1: General configuration

First you have to set up the general configuration of the system. Put the following at the top of your "extensions.conf" file:

 exten => s,1,Answer()
 exten => s,n,MeetMe(${MACRO_EXTEN},qd)
 exten => s,n,Hangup()
 exten => s,1,Answer()
 exten => s,n,Echo()
 exten => s,n,Hangup()
 ; ATC-Help
 exten => 01-ZZZZ-911.000,1,Macro(com)
 exten => 012525252591100,1,Dial(Local/01-ZZZZ-911.000)
 exten => 01-ZZZZ-910.000,1,Macro(echo)
 exten => 012525252591000,1,Dial(Local/01-ZZZZ-910.000)
 include => guest
 ; Code:
 ; 01 - FlightGear
 ; 02 - Microsoft Flight-Simulator
 ; 03 - ...
 ; Air2Air
 exten => 01-ZZZZ-123.450,1,Macro(com)
 exten => 012525252512345,1,Dial(Local/01-ZZZZ-123.450)
 exten => 01-ZZZZ-122.750,1,Macro(com)
 exten => 012525252512275,1,Dial(Local/01-ZZZZ-122.750)

Part 2: Adding your favorite (all?) frequencies

For this you have simply to create an extension for every touple of airport/frequency in extensions.conf. The following is an example for Berlin-Tempelhof (EDDI). The information comes from the file "apt.dat.gz" of your FlightGear installation.

 ; EDDI ATIS 126.020 - Berlin Tempelhof
 exten => 01-EDDI-126.020,1,Macro(com)
 exten => 010403030812602,1,Dial(Local/01-EDDI-126.020)
 ; EDDI BERLIN DEP 120.620 - Berlin Tempelhof
 exten => 01-EDDI-120.620,1,Macro(com)
 exten => 010403030812062,1,Dial(Local/01-EDDI-120.620)
 ; EDDI BERLIN DIRECTOR 121.120 - Berlin Tempelhof
 exten => 01-EDDI-121.120,1,Macro(com)
 exten => 010403030812112,1,Dial(Local/01-EDDI-121.120)
 ; EDDI BERLIN ARR 126.420 - Berlin Tempelhof
 exten => 01-EDDI-126.420,1,Macro(com)
 exten => 010403030812642,1,Dial(Local/01-EDDI-126.420)
 ; EDDI GND 121.950 - Berlin Tempelhof
 exten => 01-EDDI-121.950,1,Macro(com)
 exten => 010403030812195,1,Dial(Local/01-EDDI-121.950)
 ; EDDI TWR 119.570 - Berlin Tempelhof
 exten => 01-EDDI-119.570,1,Macro(com)
 exten => 010403030811957,1,Dial(Local/01-EDDI-119.570)
 ; EDDI BERLIN DIRECTOR 136.100 - Berlin Tempelhof
 exten => 01-EDDI-136.100,1,Macro(com)
 exten => 010403030813610,1,Dial(Local/01-EDDI-136.100)
 ; EDDI TWR 118.100 - Berlin Tempelhof
 exten => 01-EDDI-118.100,1,Macro(com)
 exten => 010403030811810,1,Dial(Local/01-EDDI-118.100)
 ; EDDI BERLIN DEP 119.500 - Berlin Tempelhof
 exten => 01-EDDI-119.500,1,Macro(com)
 exten => 010403030811950,1,Dial(Local/01-EDDI-119.500)
 ; EDDI BERLIN ARR 119.620 - Berlin Tempelhof
 exten => 01-EDDI-119.620,1,Macro(com)
 exten => 010403030811962,1,Dial(Local/01-EDDI-119.620)

What does the above mean? There are two lines (three with the comment) for each frequency: The first one sets up an extension named "01-EDDI-119.500". Yes, for VoIP you can use textual extensions but be careful if you want to setup your Asterisk-Server with POTS (=Plain old telephone service). Therefor you need the second line which is the same as above but without dashes and the letters in the decimal representation of the ASCII Code. The second line does only a "rewrite" of the numerical representation to the textual one.

For setting up all airports you can write your own simple script. But this maybe also not needed in further versions of FGCOM.

After editing the extensions.conf file you have to reload the extensions file (e.g. "asterisk -rx extensions reload").

You can add further nice goodies to your extensions.conf: MorseCode() for morsing the code of the VOR (MorseCode() will only work in Asterisk >= 1.4), Recording of metar data and playing this recording back when using the frequency of the metar information, ...

Setting up user accounts

The user accounts are located in the file iax.conf (and perhaps also in sip.conf, but this is not necessary). The top of the file should look like this:

 callerid=Guest IAX User

You may want to disallow more codecs or want to allow additional codecs (such as speex). But have in mind that the internal mixing of the conferences are done in "ulaw". But "ulaw" needs about 80 kBit/s because it does no compression. So you have to think about what's better for you: less bandwidth (per user) and more CPU usage or more bandwidth (per user) and less CPU usage... you should also consider the "sound" of some codecs may not have the 'real radio sound'.

For each user you have to add a bunch of lines to your iax.conf file:


You just have to fill in the <USERNAME> and <PASSWORD>. After each change you have to reload the configuration (e.g. "asterisk -rx reload"). Perhaps you want to write scripts for automatic configuration and so on. But be warned: Further versions of fgcom may use the multiplayer servers for getting usernames and position data and you have to change your scripts.


If you have problems you can contact me via email at "dcoredump AT".

External links



See also