systemd sd-varlink 3 sd-varlink APIs for Varlink IPC #include <systemd/sd-varlink.h> pkg-config --cflags --libs libsystemd sd-varlink.h is part of libsystemd3 and provides APIs for implementing Varlink IPC clients and services. See for more information about Varlink IPC. Varlink IPC uses JSON as marshalling format. The sd-varlink API relies on the sd-json3 API for JSON serialization, deserialization and manipulation. Canonical encoding rules: sd-varlink omits the "parameters" member on the wire in replies, errors, and notifications when there are no parameters to transmit. This reduces message size and avoids ambiguity. Receivers must be tolerant and accept any of the following encodings for the absence of parameters: an omitted "parameters" key (preferred), a JSON null value, or an empty object {}. When decoding, sd-varlink treats JSON null as if the member was omitted. The varlinkctl1 tool makes the functionality implemented by sd-varlink available from the command line. systemd1 sd-event3 sd-json3 varlinkctl1 sd-bus3 pkg-config1