sd_bus_process(3) — Linux manual page


SD_BUS_PROCESS(3)            sd_bus_process            SD_BUS_PROCESS(3)

NAME         top

       sd_bus_process - Drive the connection

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       int sd_bus_process(sd_bus *bus, sd_bus_message **ret);

DESCRIPTION         top

       sd_bus_process() drives the connection between the client and the
       message bus. That is, it handles connecting, authentication, and
       processing of messages. When invoked, pending I/O work is
       executed, and queued incoming messages are dispatched to
       registered callbacks. Each time it is invoked a single operation
       is executed. It returns zero when no operations were pending and
       positive if a message was processed. When zero is returned the
       caller should poll for I/O events before calling into
       sd_bus_process() again. For that either use the simple, blocking
       sd_bus_wait(3) call, or hook up the bus connection object to an
       external or manual event loop using sd_bus_get_fd(3).

       sd_bus_process() processes at most one incoming message per call.
       If the parameter ret is not NULL and the call processed a
       message, *ret is set to this message. The caller owns a reference
       to this message and should call sd_bus_message_unref(3) when the
       message is no longer needed. If ret is not NULL, progress was
       made, but no message was processed, *ret is set to NULL.

       If the bus object is connected to an sd-event(3) event loop (with
       sd_bus_attach_event(3)), it is not necessary to call
       sd_bus_process() directly as it is invoked automatically when

RETURN VALUE         top

       If progress was made, a positive integer is returned. If no
       progress was made, 0 is returned. If an error occurs, a negative
       errno-style error code is returned.

       Returned errors may indicate the following problems:

           An invalid bus object was passed.

           The bus connection was allocated in a parent process and is
           being reused in a child process after fork().

           The bus connection has been terminated already.

           The bus connection has been terminated just now.

           This function is already being called, i.e.  sd_bus_process()
           has been called from a callback function that itself was
           called by sd_bus_process().

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

HISTORY         top

       sd_bus_process() was added in version 231.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_wait(3), sd_bus_get_fd(3),
       sd_bus_message_unref(3), sd-event(3), sd_bus_attach_event(3)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  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

systemd 255                                            SD_BUS_PROCESS(3)

Pages that refer to this page: sd-bus(3)sd_bus_attach_event(3)sd_bus_get_fd(3)sd_bus_get_n_queued_read(3)sd_bus_send(3)sd_bus_start(3)sd_bus_wait(3)systemd.directives(7)systemd.index(7)