sd_event_add_signal man page

sd_event_add_signal, sd_event_source_get_signal — Add a signal event source to an event loop


#include <systemd/sd-bus.h>

int sd_event_add_signal(sd_event *event, sd_event_source **source, int signal, sd_event_signal_handler_t handler, void *userdata);
typedef int (*sd_event_signal_handler_t)(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata);
int sd_event_source_get_signal(sd_event_source *source);


sd_event_add_signal() adds a new signal event source to an event loop object. The event loop is specified in event, the event source is returned in the source parameter. The signal parameter specifies the signal to be handled (see signal(7)). The handler must reference a function to call when the signal is delivered or be NULL. The handler function will be passed the userdata pointer, which may be chosen freely by the caller. The handler also receives a pointer to a const struct signalfd_siginfo containing the information about the received signal. See signalfd(2) for further information.

Only a single handler may be installed for a specific signal. The signal will be unblocked, and must be blocked when the function is called. If the handler is not specified (handler is NULL), a default handler which causes the program to exit will be used. By default, the handler is enabled permanently (SD_EVENT_ON), but this may be changed with sd_event_source_set_enabled(3). If the handler function returns a negative error code, it will be disabled after the invocation, even if SD_EVENT_ON mode is set.

sd_event_source_get_signal() retrieves the configured signal number of a signal event source created previously with sd_event_add_signal(). It takes the event source object as the source parameter.

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:

Not enough memory to allocate an object.
An invalid argument has been passed.
An handler is already installed for this signal or the signal was not blocked previously.
The event loop is already terminated.
The event loop has been created in a different process.


sd_event_add_signal() and the other functions described here 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-event(3), sd_event_new(3), sd_event_add_time(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_source_set_enabled(3)

Referenced By

sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_new(3), sd_event_run(3), sd_event_set_name(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_enabled(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_event_wait(3), systemd.directives(7), systemd.index(7).

Explore man page connections for sd_event_add_signal(3).

sd_event_signal_handler_t(3) and sd_event_source_get_signal(3) are aliases of sd_event_add_signal(3).