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sd-varlink(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | NOTES | SEE ALSO | NOTES | COLOPHON 

SD-VARLINK(3)                   sd-varlink                  SD-VARLINK(3)

NAME         top

       sd-varlink - APIs for Varlink IPC

SYNOPSIS         top

       #include <systemd/sd-varlink.h>

       pkg-config --cflags --libs libsystemd

DESCRIPTION         top

       sd-varlink.h is part of libsystemd(3) and provides APIs for
       implementing Varlink IPC clients and services. See
       https://varlink.org/ for more information about Varlink IPC.

       Varlink IPC uses JSON[1] as marshalling format. The sd-varlink API
       relies on the sd-json(3) 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 varlinkctl(1) tool makes the functionality implemented by
       sd-varlink available from the command line.

NOTES         top

       Functions described here are available as a shared library, which
       can be compiled against and linked to with the
       libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be
       not multi-thread-safe. This means that the code calling the
       functions described here must not call setenv(3) from a parallel
       thread. It is recommended to only do calls to setenv() from an
       early phase of the program when no other threads have been
       started.

SEE ALSO         top

       systemd(1), sd-event(3), sd-json(3), varlinkctl(1), sd-bus(3),
       pkg-config(1)

NOTES         top

        1. JSON
           https://json.org/

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a
       bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2026-01-16.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2026-01-16.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there is
       a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 260~devel                                           SD-VARLINK(3)

Pages that refer to this page: libsystemd(3),  sd-bus(3),  sd-json(3),  sd_json_dispatch_string(3),  sd_varlink_is_connected(3),  sd_varlink_push_fd(3),  sd_varlink_send(3),  sd_varlink_server_new(3),  sd_varlink_set_description(3),  sd_varlink_set_relative_timeout(3),  systemd.directives(7),  systemd.index(7)

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