Index · Directives systemd 238


sd_bus_set_watch_bind, sd_bus_get_watch_bind — Control socket binding watching on bus connections


#include <systemd/sd-bus.h>
int sd_bus_set_watch_bind(sd_bus *bus,
 int b);
int sd_bus_get_watch_bind(sd_bus *bus);


sd_bus_set_watch_bind() may be used to enable or disable client-side watching of server socket binding for a bus connection object. If the b is true, the feature is enabled, otherwise disabled (which is the default). When enabled, and the selected bus address refers to an AF_UNIX socket in the file system which does not exist while the connection attempt is made an inotify(7) watch is installed on it, waiting for the socket to appear. As soon as the socket appears the connection is made. This functionality is useful in particular in early-boot programs that need to run before the system bus is available, but want to connect to it the instant it may be connected to.

sd_bus_get_watch_bind() may be used to query the current setting of this feature. It returns zero when the feature is disabled, and positive if enabled.

Note that no timeout is applied while it is waited for the socket to appear. This means that any synchronous remote operation (such as sd_bus_call(3), sd_bus_add_match(3) or sd_bus_request_name(3)), that is used on a connection with this feature enabled that is not established yet might block unbounded if the socket is never created. However, asynchronous remote operations (such as sd_bus_send(3), sd_bus_add_match_async(3) or sd_bus_request_match_async(3)) do not block in this case, and safely enqueue the requested operations to be dispatched the instant the connection is set up.

Use sd_bus_is_ready(3) to determine whether the connection is fully established, i.e. whether the peer socket has been bound, connected to and authenticated. Use sd_bus_set_connected_signal(3) to be notified when the connection is fully established.

Return Value

On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.


Returned errors may indicate the following problems:


The bus connection has been created in a different process.


sd_bus_set_watch_bind() and sd_bus_get_watch_bind() are available as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

See Also

systemd(1), sd-bus(3), inotify(7), sd_bus_call(3), sd_bus_add_match(3), sd_bus_request_name(3), sd_bus_is_ready(3), sd_bus_set_connected_signal(3)