sigqueue(2)sigqueue(2)NAMEsigqueue() - queue a signal to a process
SYNOPSISDESCRIPTION
The system call causes the signal specified by signo to be sent with
the value specified by value to the process specified by pid. If signo
is zero (the null signal), error checking is performed but no signal is
actually sent. The null signal can be used to check the validity of
pid.
The conditions required for a process to have permission to queue a
signal to another process are the same as for the system call.
The system call returns immediately. If is set for signo at the
receiving process (see sigqueue(2)) and if resources are available to
queue the signal, the signal will be queued and sent to the receiving
process. When the signal is delivered or accepted, the field si_value
of the siginfo parameter (see signal(5)) will be set to value. If is
not set for signo, then signo, but not necessarily value, will be sent
at least once to the receiving process.
If the value of pid causes signo to be generated for the sending
process, and if signo is not blocked, either signo or at least one
pending unblocked signal will be delivered to the sending process
before the system call returns. Should any of multiple pending signals
in the range to be selected for delivery or acceptance, it will be the
lowest numbered one. The selection order between realtime and non-
realtime signals, or between multiple pending non-realtime signals, is
unspecified.
Application Usage
Threads Considerations
can be used to post signals to another process but can not be used to
post signals to a specific thread in another process.
If the value of pid causes signo to be generated for the sending
process, and if signo is not blocked for the calling thread and if no
other thread has signo unblocked or is waiting in a function for signo,
either signo or at least one pending unblocked signal will be delivered
to the calling thread before the function returns.
LWP Considerations
Signals can not be posted to specific Lightweight Processes (LWPs) in
another process.
Security Restrictions
Some or all of the actions associated with this system call are subject
to compartmental restrictions. See compartments(5) for more information
about compartmentalization on systems that support that feature. Com‐
partmental restrictions can be overridden if the process possesses the
privilege (COMMALLOWED). Processes owned by the superuser may not have
this privilege. Processes owned by any user may have this privilege,
depending on system configuration.
Some or all of the actions associated with this system call require one
or more privileges. Processes owned by the superuser have many, though
not all, privileges. Processes owned by other users may have privi‐
lege(s), depending on system configuration. See privileges(5) for more
information about privileged access on systems that support fine-
grained privileges.
RETURN VALUE
Upon successful completion, the specified signal will be queued, and
the function returns a value of (zero). Otherwise, a value of is
returned, and is set to indicate the error.
ERRORS
fails and no signal is sent if any of the following conditions occur:
No resources are available to queue the signal.
The process has already queued signals that are
still pending at the receiver(s), or a systemwide
resource limit has been exceeded.
The value of the
signo argument is an invalid or unsupported sig‐
nal number.
The process does not have the appropriate privilege
to send the signal to the receiving process.
The process pid does not exist.
SEE ALSOkill(2), sysconf(2), privileges(5), signal(5).
sigqueue(2)
