sd_bus_new(3) — Linux manual page


SD_BUS_NEW(3)                  sd_bus_new                  SD_BUS_NEW(3)

NAME         top

       sd_bus_new, sd_bus_ref, sd_bus_unref, sd_bus_unrefp,
       sd_bus_close_unref, sd_bus_close_unrefp,
       sd_bus_flush_close_unref, sd_bus_flush_close_unrefp - Create a
       new bus object and create or destroy references to it

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       int sd_bus_new(sd_bus **bus);

       sd_bus *sd_bus_ref(sd_bus *bus);

       sd_bus *sd_bus_unref(sd_bus *bus);

       sd_bus *sd_bus_close_unref(sd_bus *bus);

       sd_bus *sd_bus_flush_close_unref(sd_bus *bus);

       void sd_bus_unrefp(sd_bus **busp);

       void sd_bus_close_unrefp(sd_bus **busp);

       void sd_bus_flush_close_unrefp(sd_bus **busp);

DESCRIPTION         top

       sd_bus_new() creates a new bus object. This object is
       reference-counted, and will be destroyed when all references are
       gone. Initially, the caller of this function owns the sole
       reference and the bus object will not be connected to any bus. To
       connect it to a bus, make sure to set an address with
       sd_bus_set_address(3) or a related call, and then start the
       connection with sd_bus_start(3).

       In most cases, it is better to use sd_bus_default_user(3),
       sd_bus_default_system(3) or related calls instead of the more
       low-level sd_bus_new() and sd_bus_start(). The higher-level
       functions not only allocate a bus object but also start the
       connection to a well-known bus in a single function call.

       sd_bus_ref() increases the reference counter of bus by one.

       sd_bus_unref() decreases the reference counter of bus by one.
       Once the reference count has dropped to zero, bus is destroyed
       and cannot be used anymore, so further calls to sd_bus_ref() or
       sd_bus_unref() are illegal.

       sd_bus_unrefp() is similar to sd_bus_unref() but takes a pointer
       to a pointer to an sd_bus object. This call is useful in
       conjunction with GCC's and LLVM's Clean-up Variable Attribute[1].
       Note that this function is defined as an inline function. Use a
       declaration like the following, in order to allocate a bus object
       that is freed automatically as the code block is left:

             __attribute__((cleanup(sd_bus_unrefp))) sd_bus *bus = NULL;
             int r;
             r = sd_bus_default(&bus);
             if (r < 0) {
               errno = -r;
               fprintf(stderr, "Failed to allocate bus: %m\n");

       sd_bus_ref() and sd_bus_unref() execute no operation if the
       argument is NULL.  sd_bus_unrefp() will first dereference its
       argument, which must not be NULL, and will execute no operation
       if that is NULL.

       sd_bus_close_unref() is similar to sd_bus_unref(), but first
       executes sd_bus_close(3), ensuring that the connection is
       terminated before the reference to the connection is dropped and
       possibly the object freed.

       sd_bus_flush_close_unref() is similar to sd_bus_unref(), but
       first executes sd_bus_flush(3) as well as sd_bus_close(3),
       ensuring that any pending messages are synchronously flushed out
       before the reference to the connection is dropped and possibly
       the object freed. This call is particularly useful immediately
       before exiting from a program as it ensures that any pending
       outgoing messages are written out, and unprocessed but queued
       incoming messages released before the connection is terminated
       and released.

       sd_bus_close_unrefp() is similar to sd_bus_close_unref(), but may
       be used in GCC's and LLVM's Clean-up Variable Attribute, see
       above. Similarly, sd_bus_flush_close_unrefp() is similar to

RETURN VALUE         top

       On success, sd_bus_new() returns 0 or a positive integer. On
       failure, it returns a negative errno-style error code.

       sd_bus_ref() always returns the argument.

       sd_bus_unref() and sd_bus_flush_close_unref() always return NULL.

       Returned errors may indicate the following problems:

           Memory allocation failed.

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_new(), sd_bus_ref(), and sd_bus_unref() were added in
       version 209.

       sd_bus_unrefp() was added in version 229.

       sd_bus_flush_close_unref() and sd_bus_flush_close_unrefp() were
       added in version 240.

       sd_bus_close_unref() and sd_bus_close_unrefp() were added in
       version 241.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_default_user(3),
       sd_bus_default_system(3), sd_bus_open_user(3),
       sd_bus_open_system(3), sd_bus_close(3)

NOTES         top

        1. Clean-up Variable Attribute

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 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  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 257~devel                                          SD_BUS_NEW(3)

Pages that refer to this page: sd-bus(3)sd_bus_close(3)sd_bus_default(3)sd_bus_message_get_cookie(3)sd_bus_message_get_monotonic_usec(3)sd_bus_message_new(3)sd_bus_message_set_destination(3)sd_bus_request_name(3)sd_bus_set_address(3)sd_bus_slot_ref(3)systemd.directives(7)systemd.index(7)