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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_BUS_PROCESS(3) sd_bus_process SD_BUS_PROCESS(3)
sd_bus_process - Drive the connection
#include <systemd/sd-bus.h>
int sd_bus_process(sd_bus *bus, sd_bus_message **ret);
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 and progress was made, but
no message was processed, *ret is set to NULL. Note that only
messages not already handled by the various types of registered
message handlers (i.e. by filters registered via
sd_bus_add_filter(3), object handlers registered via
sd_bus_add_object(3), matches registered via sd_bus_add_match(3),
and related) will be returned through this parameter. Also note
that if such a message handler returns a zero return value (as
opposed to some value > 0) an incoming message will not be
considered handled, and be passed to other suitable handlers
(until one returns > > 0), or returned by sd_bus_process() (in
case none returns > 0).
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
necessary.
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.
Errors
Returned errors may indicate the following problems:
-EINVAL
An invalid bus object was passed.
-ECHILD
The bus connection was allocated in a parent process and is
being reused in a child process after fork().
-ENOTCONN
The bus connection has been terminated already.
-ECONNRESET
The bus connection has been terminated just now.
-EBUSY
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().
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
All functions listed here are thread-agnostic and only a single
thread may operate on a given object at any given time. Different
threads may access the same object at different times. Multiple
independent objects may be used from different threads in
parallel.
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_process() was added in version 221.
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)
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 2026-08-04. (At that
time, the date of the most recent commit that was found in the
repository was 2026-08-03.) 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 262~devel 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)
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HTML rendering created 2026-09-09 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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