sd_bus_send(3) — Linux manual page


SD_BUS_SEND(3)                 sd_bus_send                SD_BUS_SEND(3)

NAME         top

       sd_bus_send, sd_bus_send_to, sd_bus_message_send - Queue a D-Bus
       message for transfer

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       int sd_bus_send(sd_bus *bus, sd_bus_message *m,
                       uint64_t *cookie);

       int sd_bus_send_to(sd_bus *bus, sd_bus_message *m,
                          const char *destination, uint64_t *cookie);

       int sd_bus_message_send(sd_bus_message *m);

DESCRIPTION         top

       sd_bus_send() queues the bus message object m for transfer. If
       bus is NULL, the bus that m is attached to is used.  bus only
       needs to be set when the message is sent to a different bus than
       the one it's attached to, for example when forwarding messages.
       If the output parameter cookie is not NULL, it is set to the
       message identifier. This value can later be used to match
       incoming replies to their corresponding messages. If cookie is
       set to NULL and the message is not sealed, sd_bus_send() assumes
       the message m doesn't expect a reply and adds the necessary
       headers to indicate this.

       Note that in most scenarios, sd_bus_send() should not be called
       directly. Instead, use higher level functions such as
       sd_bus_call_method(3) and sd_bus_reply_method_return(3) which
       call sd_bus_send() internally.

       sd_bus_send_to() is a shorthand for sending a message to a
       specific destination. It's main use case is to simplify sending
       unicast signal messages (signals that only have a single
       receiver). It's behavior is similar to calling
       sd_bus_message_set_destination(3) followed by calling

       sd_bus_send()/sd_bus_send_to() will write the message directly to
       the underlying transport (e.g. kernel socket buffer) if possible.
       If the connection is not set up fully yet the message is queued
       locally. If the transport buffers are congested any unwritten
       message data is queued locally, too. If the connection has been
       closed or is currently being closed the call fails.
       sd_bus_process(3) should be invoked to write out any queued
       message data to the transport.

       sd_bus_message_send() is the same as sd_bus_send() but without
       the first and last argument.  sd_bus_message_send(m) is
       equivalent to sd_bus_send(sd_bus_message_get_bus(m), m, NULL).

RETURN VALUE         top

       On success, these functions return a non-negative integer. On
       failure, they return a negative errno-style error code.

       Returned errors may indicate the following problems:

           The input parameter m is NULL.

           Added in version 246.

           The bus connection does not support sending file descriptors.

           Added in version 246.

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

           Added in version 246.

           The bus connection's write queue is full.

           Added in version 246.

           The input parameter bus is NULL or the bus is not connected.

           Added in version 246.

           The bus connection was closed while waiting for the response.

           Added in version 246.

           Memory allocation failed.

           Added in version 246.

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_send() and sd_bus_send_to() were added in version 246.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_call_method(3),
       sd_bus_message_set_destination(3), sd_bus_reply_method_return(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 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_SEND(3)

Pages that refer to this page: sd-bus(3)sd_bus_default(3)sd_bus_emit_signal(3)sd_bus_enqueue_for_read(3)sd_bus_get_n_queued_read(3)sd_bus_message_seal(3)sd_bus_set_watch_bind(3)sd_bus_start(3)systemd.directives(7)systemd.index(7)