HPUX sigaction[2]
sigaction(2) sigaction(2)
NAME
sigaction - examine and change signal action
SYNOPSIS
#include <signal.h>
int sigaction (
int sig,
const struct sigaction *act,
struct sigaction *oact
);
DESCRIPTION
sigaction() allows the calling process to examine and specify the
action to be taken on delivery of a specific signal. The argument sig
specifies the signal; acceptable values are defined in <signal.h>.
More details on the semantics of specific signals can be found in the
signal(5) manual entry.
The sigaction structure and type sigset_t are defined in <signal.h>.
act and oact are pointers to sigaction structures that include the
following elements:
void (*sa_handler)();
sigset_t sa_mask;
int sa_flags;
Unless it is a null pointer, the argument act points to a structure
specifying the action to be taken when delivering the specified
signal. If the argument oact is not a null pointer, the action
previously associated with the signal is stored in the location
pointed to by oact. If the argument act is a null pointer, signal
handling is unchanged; thus sigaction() can be used to inquire about
the current handling of a given signal.
The sa_handler member of the sigaction structure is assigned one of
three values: SIG_DFL, SIG_IGN, or a function address. The actions
prescribed by these values are as follows:
SIG_DFL Execute default action for signal.
Upon receipt of the signal sig, the default
action (specified on signal(5)) is performed.
The default action for most signals is to
terminate the process.
A pending signal is discarded (whether or not
it is blocked) if sigaction() is set to SIG_DFL
for a pending signal whose default action is to
ignore the signal (as in the case of SIGCHLD).
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SIG_IGN Ignore the signal.
Setting a signal action to SIG_IGN causes a
pending signal to be discarded, whether or not
it is blocked.
The SIGKILL and SIGSTOP signals cannot be
ignored.
function address Catch the signal.
Upon receipt of the signal sig, the receiving
process executes the signal-catching function
pointed to by sa_handler. The signal-catching
function is entered as a C-language function
call. Details on the arguments passed to this
function can be found in the signal(5) manual
entry.
The signals SIGKILL and SIGSTOP cannot be
caught.
When a signal is caught by a signal-catching function installed
by sigaction, a new mask is calculated and installed for the
duration of the signal-catching function, or until a call is made
to sigprocmask() or sigsuspend() (see sigprocmask(2) and
sigsuspend(2)). This mask is formed by taking the union of the
current signal mask, the signal to be delivered, and unless the
SA_RESETHAND flag is set (see below), the signal mask specified
in the sa_mask field of the sigaction structure associated with
the signal being delivered. If and when the signal-catching
function returns normally, the original signal mask is restored.
Once an action is installed for a specific signal, it remains
installed until another action is explicitly requested, or until
one of the exec(2) functions is called.
If the previous action for sig was established by signal(2), the
values of the fields returned in the structure pointed to by oact
are unspecified; in particular, oact->sa_handler is not
necessarily the same value passed to signal(). However, if a
pointer to the same structure or a copy thereof is passed to a
subsequent call to sigaction() via the act argument, handling of
the signal is reinstated as if the original call to signal() were
repeated.
The set of signals specified by the sa_mask field of the
sigaction structure pointed to by the act argument cannot block
the SIGKILL or SIGSTOP signal. This is enforced by the system
without causing an error to be indicated.
The sa_flags field in the sigaction structure can be used to
modify the behavior of the specified signal. The following flag
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bits, defined in the <signal.h> header, can be set in sa_flags:
SA_NOCLDSTOP Do not generate SIGCHLD when untraced
children stop (see ptrace(2)).
SA_ONSTACK Use the space reserved by sigspace() for
signal processing.
SA_RESETHAND Use the semantics of signal(). The
signal mask specified by the sa_mask
field is not used when setting up the
effective signal mask for the signal
handler. If the signal is not one of
those marked "not reset when caught"
(see signal(5)), the default action for
the signal is reinstated when the signal
is caught, prior to entering the
signal-catching function. The "not
reset when caught" distinction is
insignificant when sigaction() is called
and SA_RESETHAND is not set.
RETURN VALUE
Upon successful completion, sigaction() returns 0; otherwise it
returns -1 and sets errno to indicate the error.
ERRORS
sigaction() fails and no new signal-catching function is installed if
any of the following conditions is encountered:
[EINVAL] The value of the sig argument is not a valid
signal number, or an attempt is made to
supply an action other than SIG_DFL for the
SIGKILL or SIGSTOP signal.
[EFAULT] act or oact points to an invalid address.
The reliable detection of this error is
implementation dependent.
AUTHOR
sigaction() was derived from the IEEE POSIX 1003.1-1988 Standard.
SEE ALSO
ptrace(2), sigprocmask(2), sigpending(2), sigspace(2), sigsuspend(2),
sigsetops(3C), signal(5).
STANDARDS CONFORMANCE
sigaction(): AES, XPG3, XPG4, FIPS 151-2, POSIX.1
Hewlett-Packard Company - 3 - HP-UX Release 9.0: August 1992