GNU Radio Manual and C++ API Reference
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Configuration files

Configuration / Preference Files

GNU Radio defines some of its basic behavior through a set of configuration files located in ${prefix}/etc/gnuradio/conf.d. Different components have different files listed in here for the various properties. These will be read once when starting a GNU Radio application, so updates during runtime will not affect them.

The configuration files use the following format:

# Stuff from section 1
var1 = value1
var2 = value2 # value of 2
# Stuff from section 2
var3 = value3

In this file, the hash mark ('#') indicates a comment and blank lines are ignored. Section labels are defined inside square brackets as a group distinguisher. All options must be associated with a section name. The options are listed one per line with the option name is given followed by an equals ('=') sign and then the value.

All section and option names must not have white spaces. If a value must have white space, the it MUST be put inside quotes. Any quoted value will have its white space preserved and the quotes internally will be stripped. As an example, on Apple desktops, an output device of "Display Audio" is a possible output device and can be set as:

default_output_device = "Display Audio"

The result will pass Display Audio to the audio setup.

The value of an option can be a string or number and retrieved through a few different interfaces. There is a single preference object created when GNU Radio is launched. In Python, you can get this by making a new variable:

p = gr.prefs()

Similarly, in C++, we get a reference to the object by explicitly calling for the singleton of the object:

prefs *p = prefs::singleton();

The methods associated with this preferences object are (from class gr::prefs):

bool has_section(string section)
bool has_option(string section, string option)
string get_string(string section, string option, string default_val)
bool get_bool(string section, string option, bool default_val)
long get_long(string section, string option, long default_val)
double get_double(string section, string option, double default_val)

When setting a Boolean value, we can use 0, 1, "True", "true", "False", "false", "On", "on", "Off", and "off".

All configuration preferences in these files can also be overloaded by an environmental variable. The environmental variable is named based on the section and option name from the configuration file as:


The "GR_CONF_" is a prefix to identify this as a GNU Radio configuration variable and the section and option names are in uppercase. The value is the same format that would be used in the config file itself.