Index · Directives systemd 255


sd_bus_wait — Wait for I/O on a bus connection


#include <systemd/sd-bus.h>
int sd_bus_wait(sd_bus *bus,
 uint64_t timeout_usec);


sd_bus_wait() synchronously waits for I/O on the specified bus connection object. This function is supposed to be called whenever sd_bus_process(3) returns zero, indicating that no work is pending on the connection. Internally, this call invokes ppoll(2), to wait for I/O on the bus connection. If the timeout_usec parameter is specified, the call will block at most for the specified amount of time in μs. Pass UINT64_MAX to permit it to sleep indefinitely.

After each invocation of sd_bus_wait() the sd_bus_process() call should be invoked in order to process any now pending I/O work.

Note that sd_bus_wait() is suitable only for simple programs as it does not permit waiting for other I/O events. For more complex programs either connect the bus connection object to an external event loop using sd_bus_get_fd(3) or to an sd-event(3) event loop using sd_bus_attach_event(3).

Return Value

If any I/O was seen, a positive value is returned, zero otherwise. If an error occurs, a negative errno-style error code is returned.


Returned errors may indicate the following problems:


An invalid bus object was passed.


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


The bus connection has been terminated already.


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_wait() was added in version 240.

See Also

systemd(1), sd-bus(3), sd_bus_process(3), sd_bus_get_fd(3), sd-event(3), sd_bus_attach_event(3)