Changing PID file location

When the program is run in background, it stores its PID in the /run/rtl_airband.pid file by default. This directory is usually not writable for non-root users, so if you prefer to run RTLSDR-Airband on a non-privileged user account, you may need to choose a different PID path. To do this, use pidfile configuration option in the global section. Example:

pidfile = "/var/tmp/rtl_airband.pid";

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Note: When RTLSDR-Airband is run as a systemd service of type simple (as described here), changing this option is not necessary. In this mode it's systemd's job to register the PID of the service. RTLSDR-Airband does not write a PID file in this case.