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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_EVENT_ADD_SIGNAL(3) sd_event_add_signal SD_EVENT_ADD_SIGNAL(3)
sd_event_add_signal, sd_event_source_get_signal,
sd_event_signal_handler_t, SD_EVENT_SIGNAL_PROCMASK - Add a UNIX
process signal event source to an event loop
#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
SD_EVENT_SIGNAL_PROCMASK
typedef int (*sd_event_signal_handler_t)(sd_event_source *s,
const struct signalfd_siginfo *si,
void *userdata);
int sd_event_add_signal(sd_event *event, sd_event_source **source,
int signal,
sd_event_signal_handler_t handler,
void *userdata);
int sd_event_source_get_signal(sd_event_source *source);
sd_event_add_signal() adds a new UNIX process signal event source
to an event loop. The event loop object is specified in the event
parameter, and the event source object is returned in the source
parameter. The signal parameter specifies the numeric signal to be
handled (see signal(7)).
The handler parameter is a function to call when the signal is
received or 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 signalfd_siginfo structure containing
information about the received signal. See signalfd(2) for further
information. The handler may return negative to signal an error
(see below), other return values are ignored. If handler is NULL,
a default handler that calls sd_event_exit(3) will be used.
Only a single handler may be installed for a specific signal. The
signal must be blocked in all threads before this function is
called (using sigprocmask(2) or pthread_sigmask(3)). For
convenience, if the special flag SD_EVENT_SIGNAL_PROCMASK is ORed
into the specified signal the signal will be automatically masked
as necessary, for the calling thread. Note that this only works
reliably if the signal is already masked in all other threads of
the process, or if there are no other threads at the moment of
invocation.
By default, the event source 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 either
be disabled after the invocation, even if the SD_EVENT_ON mode was
requested before, or it will cause the loop to terminate, see
sd_event_source_set_exit_on_failure(3).
To destroy an event source object use sd_event_source_unref(3),
but note that the event source is only removed from the event loop
when all references to the event source are dropped. To make sure
an event source does not fire anymore, even if it is still
referenced, disable the event source using
sd_event_source_set_enabled(3) with SD_EVENT_OFF.
If the second parameter of sd_event_add_signal() is NULL no
reference to the event source object is returned. In this case,
the event source is considered "floating", and will be destroyed
implicitly when the event loop itself is destroyed.
If the handler parameter to sd_event_add_signal() is NULL, and the
event source fires, this will be considered a request to exit the
event loop. In this case, the userdata parameter, cast to an
integer, is passed as the exit code parameter to sd_event_exit(3).
sd_event_source_get_signal() returns the configured signal number
of an event source created previously with sd_event_add_signal().
It takes the event source object as the source parameter.
On success, these functions return 0 or a positive integer. On
failure, they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-ENOMEM
Not enough memory to allocate an object.
-EINVAL
An invalid argument has been passed.
-EBUSY
A handler is already installed for this signal or the signal
was not blocked previously.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process,
library or module instance.
-EDOM
The passed event source is not a signal event source.
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_event_add_signal(), sd_event_signal_handler_t(), and
sd_event_source_get_signal() were added in version 217.
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
sd_event_add_io(3), sd_event_add_time(3), sd_event_add_child(3),
sd_event_add_inotify(3), sd_event_add_defer(3),
sd_event_source_set_enabled(3),
sd_event_source_set_description(3),
sd_event_source_set_userdata(3), sd_event_source_set_floating(3),
signal(7), signalfd(2), sigprocmask(2), pthread_sigmask(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 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 is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_EVENT_ADD_SIGNAL(3)
Pages that refer to this page: sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_inotify(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_exit(3), sd_event_new(3), sd_event_run(3), sd_event_set_signal_exit(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_destroy_callback(3), sd_event_source_set_enabled(3), sd_event_source_set_exit_on_failure(3), sd_event_source_set_floating(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_ratelimit(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 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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