sigprocmask
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NAME
sigaction, sigprocmask, sigpending, sigsuspend - POSIX
signal handling functions.
SYNOPSIS
#include <signal.h>
int sigaction(int signum, const struct sigaction *act,
struct sigaction *oldact);
int sigprocmask(int how, const sigset_t *set, sigset_t
*oldset);
int sigpending(sigset_t *set);
int sigsuspend(const sigset_t *mask);
DESCRIPTION
The sigaction system call is used to change the action for
a signal. If act is non-null, the new action for signal
signum is installed from act. If oldact is non-null, the
previous action is saved in oldact.
The sigaction structure is defined as
struct sigaction {
void (*sa_handler)();
sigset_t sa_mask;
int sa_flags;
void (*sa_restorer)(void);
}
sa_handler may be SIG_DFL for the default action, SIG_IGN
to ignore this signal, or a pointer to a signal handling
function.
sa_mask gives a mask of signals which should be blocked
during execution of the signal handler.
sa_flags is the bitwise OR of zero or more of the follow-
ing flags
SA_NOCLDSTOP
Do not generate SIGCHLD signals when child
processes terminate.
SA_ONESHOT
Restore the signal action to the default
state once the signal handler has been
called. This is the default behavior.
SA_RESTART
The opposite to SA_ONESHOT, do not restore
the signal action. This provides behavior
compatible with BSD signal semantics.
SA_NOMASK
Do not prevent the signal from being
received from within its own signal handler.
The sa_restorer element is obsolete and should not be
used.
The sigprocmask call is used to change the list of cur-
rently blocked signals. The behavior of the call is depen-
dent on the value of how, as follows.
SIG_BLOCK
The set of blocked signals is the union of
the current set and the set argument.
SIG_UNBLOCK
The signals in set are removed from the cur-
rent set of blocked signals. It is legal to
attempt to unblock a signal which is not
blocked.
SIG_SETMASK
The set of blocked signals is set to the
argument set.
If oldset is non-null, the previous value of the signal
mask is stored in oldset.
The sigpending call allows the examination of pending sig-
nals (ones which have been raised while blocked). The
signal mask of pending signals is stored in set.
The sigsuspend call temporarily replaces the signal mask
for the process with that given by mask and then suspends
the process until a signal is received.
RETURN VALUES
sigaction, sigprocmask, sigpending and sigsuspend return 0
on success and -1 on error.
ERRORS
EINVAL An invalid signal was specified. This will also be
generated if an attempt is made to change the
action for SIGKILL or SIGSTOP, which cannot be
caught.
EFAULT act, oldact or the signal handler point to memory
which is not a valid part of the process address
space.
EINTR System call was interrupted.
NOTES
It is not possible to block SIGKILL or SIGSTOP with the
sigprocmask call. Attempts to do so will be silently
ignored.
The POSIX spec only defines SA_NOCLDSTOP. Use of
SA_ONESHOT and SA_RESTART is non-portable.
sigaction can be called with a null second argument to
query the current signal handler. It can also be used to
check whether a given signal is valid for the current
machine by calling it with null second and third argu-
ments.
See sigsetops(3) for details on manipulating signal sets.
CONFORMING TO
POSIX
SEE ALSO
kill(1), kill(2), killpg(2), pause(2), raise(3), siginter-
rupt(3), signal(2), signal(7), sigsetops(3), sigvec(2)
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.