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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_BUS_SEND(3) sd_bus_send SD_BUS_SEND(3)
sd_bus_send, sd_bus_send_to, sd_bus_message_send - Queue a D-Bus
message for transfer
#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);
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
is 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 does
not 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()/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).
On success, these functions return a non-negative integer. On
failure, they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
The input parameter m is NULL.
Added in version 246.
-EOPNOTSUPP
The bus connection does not support sending file descriptors.
Added in version 246.
-ECHILD
The bus connection was allocated in a parent process and is
being reused in a child process after fork().
Added in version 246.
-ENOBUFS
The bus connection's write queue is full.
Added in version 246.
-ENOTCONN
The input parameter bus is NULL or the bus is not connected.
Added in version 246.
-ECONNRESET
The bus connection was closed while waiting for the response.
Added in version 246.
-ENOMEM
Memory allocation failed.
Added in version 246.
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.
sd_bus_send() and sd_bus_send_to() were added in version 246.
systemd(1), sd-bus(3), sd_bus_call_method(3),
sd_bus_message_set_destination(3), sd_bus_reply_method_return(3),
sd_bus_process(3)
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 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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
[email protected]
systemd 258~rc2 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_reply_method_error(3), sd_bus_reply_method_return(3), sd_bus_set_watch_bind(3), sd_bus_start(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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