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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |HISTORY |SEE ALSO |NOTES |COLOPHON | |
SD_BUS_NEW(3) sd_bus_newSD_BUS_NEW(3)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
#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);
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 withsd_bus_set_address(3) or a related call, and then start the connection withsd_bus_start(3). In most cases, it is better to usesd_bus_default_user(3),sd_bus_default_system(3) or related calls instead of the more low-levelsd_bus_new()andsd_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 ofbus by one.sd_bus_unref()decreases the reference counter ofbus by one. Once the reference count has dropped to zero,bus is destroyed and cannot be used anymore, so further calls tosd_bus_ref()orsd_bus_unref()are illegal.sd_bus_unrefp()is similar tosd_bus_unref()but takes a pointer to a pointer to ansd_busobject. This call is useful in conjunction with GCC's and LLVM'sClean-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()andsd_bus_unref()execute no operation if the argument isNULL.sd_bus_unrefp()will first dereference its argument, which must not beNULL, and will execute no operation ifthat isNULL.sd_bus_close_unref()is similar tosd_bus_unref(), but first executessd_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 tosd_bus_unref(), but first executessd_bus_flush(3) as well assd_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 tosd_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 tosd_bus_flush_close_unref().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()andsd_bus_flush_close_unref()always returnNULL.Errors Returned errors may indicate the following problems:-ENOMEM Memory allocation failed.
Functions described here are available as a shared library, which can be compiled against and linked to with thelibsystemd pkg-config(1) file. The code described here usesgetenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not callsetenv(3) from a parallel thread. It is recommended to only do calls tosetenv()from an early phase of the program when no other threads have been started.
sd_bus_new(),sd_bus_ref(), andsd_bus_unref()were added in version 209.sd_bus_unrefp()was added in version 229.sd_bus_flush_close_unref()andsd_bus_flush_close_unrefp()were added in version 240.sd_bus_close_unref()andsd_bus_close_unrefp()were added in version 241.
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)
1. Clean-up Variable Attributehttps://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
This page is part of thesystemd (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 isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_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)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |