Format of the configuration files

Configurations files use the INI format. A UHD configuration file might look like this:

; Comments start with a semicolon
; Sections are put in square brackets:
[type=b200]
; These settings apply to all USRPs that are of type b200:
master_clock_rate=20e6
[serial=FE18011]
; These settings apply to the USRPs with the given serial:
master_clock_rate=10e6 ; If this is a b200, this will overwrite the above settings

Configuring USRPs

For the most part, any setting that can get put into device args at initialization time can be put into the config file. For example, the X300 has a key called ext_adc_self_test which is disabled by default. To enable it, you can add it to your device args:

auto usrp = uhd::usrp::multi_usrp::make("type=x300,ext_adc_self_test=1");

However, this can be cumbersome if the intention is to permanently enable this for all X300s connected to this machine. To generally enable this option for all X300s without having to modify the make() call, the config file can simply be updated as such:

[type=x300]

ext_adc_self_test=1

This will act as if this key/value pair had been passed to the device args directly. This means the valid key/value pairs for the config files are the same as those for the device args (see Device Configuration through address string).

Configuring UHD Sessions

For settings that are not specific to a device, but rather to the UHD session, there is the Global section. At the time of writing this, there is only one setting available in this section which is the guided_mode which supports the user on X440 devices. For turning it off, the following can be added to the config file:

[Global]

guided_mode=false

Configuring DPDK

DPDK is a special case. Because there are so many things to configure for DPDK, it is highly recommended to use config files. The section headers for DPDK configurations depend on on the network device used, not the USRP device. For more details, see NIC Configuration.

Configuring MPM

MPM devices (N3xx, E3xx) have their own configuration file (mpm.conf) which is read once during initialization of MPM. It controls different things than the uhd.conf file (both can be used for a session, but the UHD configuration will be used at every UHD session, whereas the MPM configuration file is only read once during MPM initialization). To reload the MPM configuration file, a restart of MPM is required.

The mpm.conf files are structured a bit differently from uhd.conf, so here's an example:

; This section is for any MPM behaviour
[mpm]
; Default log level for journald, can be overwritten by -v when starting manually
log_level=info
; Number of log records to buffer for the next get_log_buf() API call
log_buf_size=100
; Device-specific behaviour is set here. This allows having the same file for
; different device types, e.g., when a fleet of different devices are
; managed via Salt or similar tools. The key here is the same as what you would
; use in device args as a type value.
[n3xx]
KEY=VALUE
; Alternatively, specify a product value.
[n310]
KEY=VALUE

The key/value pairs for the type or product sections are documented in Device Configuration through MPM configuration files.

Location of configuration files

UHD will look for up to three configuration files:

A system-wide configuration file. On Unix systems, the default location for this file is /etc/uhd/uhd.conf. On Windows systems, %programdata%/uhd/uhd.conf. The default can be overwritten at compile time by setting UHD_SYS_CONF_FILE through CMake.
A user-specific configuration file. On Unix systems, it defaults to $XDG_CONFIG_HOME/uhd.conf, where $XDG_CONFIG_HOME is usually the same as $HOME/.config. On Windows systems, it also checks %localappdata% and %appdata%. The default can be overwritten at compile time by setting the UHD_USER_CONF_FILE through CMake.
A configuration file specified by the environment variable UHD_CONFIG_FILE

UHD will read these files in this order (if they exist). Settings from one file will overwrite those from a previous one, so if the same setting exists in the system-wide file and the user-specific file, the settings from the user-specific file will take effect. There is no error if a file does not exist, or the environment variable is not set.

MPM will only look for a configuration file in /etc/uhd/mpm.conf, on the device running MPM itself.