HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)

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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

The sigaction() function allows the calling process to examine and/or specify the action to be associ-

ated with a speciﬁc signal. The argument sig speciﬁes the signal; acceptable values are deﬁned in

<signal.h>.

The structure sigaction, used to describe an action to be taken, is deﬁned in the header <signal.h> to

include at least the following members:

Member Type Member Name Description

SIG_DFL, SIG_IGN or pointer to a

function.void(*)(int) sa_handler

Additional set of signals to be blocked

during execution of signal-catching

function.sigset_t sa_mask

Special ﬂags to affect behavior of sig-

nal.int sa_flags

signal-catching function.void(*)(int, siginfo_t*,void *) sa_sigaction

If the argument act is not a null pointer, it points to a structure specifying the action to be associated with

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 the argument oact. If the argument act is a null pointer, signal

handling is unchanged; thus, the call can be used to enquire about the current handling of a given signal.

The sa_handler ﬁeld of the

sigaction structure identiﬁes the action to be associated with the speciﬁed

signal. If the sa_handler ﬁeld speciﬁes a signal-catching function, the sa_mask ﬁeld identiﬁes a set of sig-

nals that will be added to the process’ signal mask before the signal-catching function is invoked. The

SIG-

KILL

and SIGSTOP signals will not be added to the signal mask using this mechanism; this restriction

will be enforced by the system without causing an error to be indicated.

The sa_ﬂags ﬁeld can be used to modify the behavior of the speciﬁed signal. The following ﬂags, deﬁned in

the header <signal.h> , can be set in sa_ﬂags:

SA_NOCLDSTOP Do not generate SIGCHLD when children stop.

SA_ONSTACK If set and an alternate signal stack has been declared with

sigaltstack() or sigstack() , the signal will be delivered to the cal-

ling process on that stack. Otherwise, the signal will be delivered on the

current stack.

SA_RESETHAND If set, the disposition of the signal will be reset to SIG_DFL and the

SA_SIGINFO ﬂag will be cleared on entry to the signal handler (Note:

SIGILL, SIGTRAP, and SIGPWR cannot be automatically reset when

delivered; the system silently enforces this restriction). Otherwise, the dispo-

sition of the signal will not be modiﬁed on entry to the signal handler. In

addition, if this ﬂag is set, sigaction() behaves as if the SA_NODEFER

ﬂag were also set.

SA_RESTART This ﬂag affects the behaviour of interruptible functions; that is, those

speciﬁed to fail with errno set to EINTR. If set, and a function speciﬁed as

interruptible is interrupted by this signal, the function will restart and will

not fail with EINTR unless otherwise speciﬁed. If the ﬂag is not set,

HP-UX Release 11i: December 2000 − 1 − Section 2−−333

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