SIGHOLD(P) POSIX Programmer's Manual SIGHOLD(P)
sighold, sigignore, sigpause, sigrelse, sigset - signal management
int sighold(int sig);
int sigignore(int sig);
int sigpause(int sig);
int sigrelse(int sig);
void (*sigset(int sig, void (*disp)(int)))(int);
Use of any of these functions is unspecified in a multi-threaded process.
The sighold(), sigignore(), sigpause(), sigrelse(), and sigset() functions provide simpli-
fied signal management.
The sigset() function shall modify signal dispositions. The sig argument specifies the
signal, which may be any signal except SIGKILL and SIGSTOP. The disp argument specifies
the signal's disposition, which may be SIG_DFL, SIG_IGN, or the address of a signal han-
dler. If sigset() is used, and disp is the address of a signal handler, the system shall
add sig to the calling process' signal mask before executing the signal handler; when the
signal handler returns, the system shall restore the calling process' signal mask to its
state prior to the delivery of the signal. In addition, if sigset() is used, and disp is
equal to SIG_HOLD, sig shall be added to the calling process' signal mask and sig's dispo-
sition shall remain unchanged. If sigset() is used, and disp is not equal to SIG_HOLD, sig
shall be removed from the calling process' signal mask.
The sighold() function shall add sig to the calling process' signal mask.
The sigrelse() function shall remove sig from the calling process' signal mask.
The sigignore() function shall set the disposition of sig to SIG_IGN.
The sigpause() function shall remove sig from the calling process' signal mask and suspend
the calling process until a signal is received. The sigpause() function shall restore the
process' signal mask to its original state before returning.
If the action for the SIGCHLD signal is set to SIG_IGN, child processes of the calling
processes shall not be transformed into zombie processes when they terminate. If the call-
ing process subsequently waits for its children, and the process has no unwaited-for chil-
dren that were transformed into zombie processes, it shall block until all of its children
terminate, and wait(), waitid(), and waitpid() shall fail and set errno to [ECHILD].
Upon successful completion, sigset() shall return SIG_HOLD if the signal had been blocked
and the signal's previous disposition if it had not been blocked. Otherwise, SIG_ERR shall
be returned and errno set to indicate the error.
The sigpause() function shall suspend execution of the thread until a signal is received,
whereupon it shall return -1 and set errno to [EINTR].
For all other functions, upon successful completion, 0 shall be returned. Otherwise, -1
shall be returned and errno set to indicate the error.
These functions shall fail if:
EINVAL The sig argument is an illegal signal number.
The sigset() and sigignore() functions shall fail if:
EINVAL An attempt is made to catch a signal that cannot be caught, or to ignore a signal
that cannot be ignored.
The following sections are informative.
The sigaction() function provides a more comprehensive and reliable mechanism for control-
ling signals; new applications should use sigaction() rather than sigset().
The sighold() function, in conjunction with sigrelse() or sigpause(), may be used to
establish critical regions of code that require the delivery of a signal to be temporarily
The sigsuspend() function should be used in preference to sigpause() for broader portabil-
Signal Concepts , exec() , pause() , sigaction() , signal() , sigsuspend() , waitid() ,
the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SIGHOLD(P)