sigaction.2 (2010 09)

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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

signal.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 signals that will be added to the thread’s signal mask before

the signal-catching function is invoked. The

SIGKILL and SIGSTOP signals will not be added to the sig-

nal 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

disposition 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 behavior 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

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (8 pages)

PAGE 1
sigaction(2) sigaction(2) NAME sigaction - examine and change signal action SYNOPSIS #include 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 associated with a specific signal. The argument sig specifies the signal; acceptable values are defined in . The structure sigaction, used to describe an action to be taken, is defined in the header
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sigaction(2) sigaction(2) will not fail with [EINTR] unless otherwise specified. If the flag is not set, interruptible functions interrupted by this signal will fail with errno set to [EINTR]. SA_SIGINFO If cleared and the signal is caught, the signal-catching function will be entered as: void func(int signo); where signo is the only argument to the signal catching function.
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sigaction(2) sigaction(2) signal mask and the value of the sa_mask for the signal being delivered unless SA_NODEFER or SA_RESETHAND is set, and then including the signal being delivered. If and when the user’s signal handler returns normally, the original signal mask is restored.
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sigaction(2) sigaction(2) The selection order between realtime and nonrealtime signals, or between multiple pending nonrealtime signals, is unspecified. Signals generated by kill() or other events that cause signals to occur, such as detection of hardware faults, alarm() timer expiration, or terminal activity, and for which the implementation does not support queueing, will have no effect on signals already queued for the same signal number.
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sigaction(2) • sigaction(2) If SA_SIGINFO is set, the signal-catching function will be entered as: void func(int signo, siginfo_t *siginfo, void *ucontextptr); where func is the specified signal-catching function, signo is the signal number of the signal being delivered, siginfo points to an object of type siginfo_t associated with the signal being delivered, and ucontextptr points to a ucontext_t .
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sigaction(2) sigaction(2) Note that longjmp() and siglongjmp() are not in the list of reentrant functions. This is because the code executing after longjmp() and siglongjmp() can call any unsafe functions with the same danger as calling those unsafe functions directly from the signal handler. Applications that use longjmp() and siglongjmp() from within signal handlers require rigorous protection in order to be portable.
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sigaction(2) sigaction(2) WARNINGS The fpathconf() function is marked as an extension in the list of safe functions because it is not included in the corresponding list in the ISO POSIX-1 standard, but it is expected to be added in a future revision of that standard. AUTHOR sigaction() was derived from the IEEE POSIX 1003.1-1988 Standard.
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(Notes) A (Notes) sA 8 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010