SIGACTION
Section: Linux Programmer's Manual (2)
Updated: 24 September 1994
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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 following 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element is obsolete and should not be used.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 currently blocked signals. The
behavior of the call is dependent 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 current 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 signals (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 arguments.
See
sigsetops(3)
for details on manipulating signal sets.
CONFORMING TO
POSIX
SEE ALSO
kill(1), kill(2), killpg(2), pause(2), raise(3),
siginterrupt(3), signal(2), signal(7), sigsetops(3),
sigvec(2)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUES
-
- ERRORS
-
- NOTES
-
- CONFORMING TO
-
- SEE ALSO
-
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