NAME
sigqueue() — queue a signal to a process
SYNOPSIS
#include <signal.h>
int sigqueue(pid_t pid, int signo, const union sigval value);
DESCRIPTION
The
sigqueue()
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
kill()
system call.
The
sigqueue()
system call returns immediately.
If
SA_SIGINFO
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
SA_SIGINFO
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
sigqueue()
system call returns.
Should any of multiple pending signals
in the range
SIGRTMIN
to
SIGRTMAX
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
sigqueue()
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
sigwait()
function for
signo,
either
signo
or at least one pending unblocked signal
will be delivered to the calling thread
before the
sigqueue()
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.
Compartmental restrictions can be overridden if the process possesses the
PRIV_COMMALLOWED
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 privileges, 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
sigqueue()
function returns a value of
0
(zero).
Otherwise, a value of
-1
is returned,
and
errno
is set to indicate the error.
ERRORS
sigqueue()
fails and no signal is sent if
any of the following conditions occur:
- EAGAIN
No resources are available to queue the signal.
The process has already queued
{SIGQUEUE_MAX}
signals that are still pending at the receivers,
or a systemwide resource limit has been exceeded.
- EINVAL
The value of the
signo
argument is an invalid or unsupported signal number.
- EPERM
The process does not have the appropriate privilege
to send the signal to the receiving process.
- ESRCH
The process
pid
does not exist.
Printable version
