SIGSET(3) Linux Programmer's Manual SIGSET(3)
sigset, sighold, sigrelse, sigignore - System V signal API
#define _XOPEN_SOURCE 500
typedef void (*sighandler_t)(int);
sighandler_t sigset(int sig, sighandler_t disp);
int sighold(int sig);
int sigrelse(int sig);
int sigignore(int sig);
These functions are provided in glibc as a compatibility interface for
programs that make use of the historical System V signal API. This API
is obsolete: new applications should use the POSIX signal API (sigac-
tion(2), sigprocmask(2), etc.)
The sigset() function modifies the disposition of the signal sig. The
disp argument can be the address of a signal handler function, or one
of the following constants:
Reset the disposition of sig to the default.
Add sig to the process's signal mask, but leave the disposition
of sig unchanged.
If disp specifies the address of a signal handler, then sig is added to
the process's signal mask during execution of the handler.
If disp was specified as a value other than SIG_HOLD, then sig is
removed from the process's signal mask.
The dispositions for SIGKILL and SIGSTOP cannot be changed.
The sighold() function adds sig to the calling process's signal mask.
The sigrelse() function removes sig from the calling process's signal
The sigignore() function sets the disposition of sig to SIG_IGN.
On success, sigset() returns SIG_HOLD if sig was blocked before the
call, or the signal's previous disposition if it was not blocked before
the call. On error, sigset() returns -1, with errno set to indicate
the error. (But see BUGS below.)
The sighold(), sigrelse(), and sigignore() functions return 0 on suc-
cess; on error, these functions return -1 and set errno to indicate the
For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).
For sighold() and sigrelse() see the ERRORS under sigprocmask(2).
For sigignore(), see the errors under sigaction(2).
SVr4, POSIX.1-2001. These functions are obsolete: do not use them in
These functions appeared in glibc version 2.1.
The sighandler_t type is a GNU extension; it is only used on this page
to make the sigset() prototype more easily readable.
The sigset() function provides reliable signal handling semantics (as
when calling sigaction(2) with sa_mask equal to 0).
On System V, the signal() function provides unreliable semantics (as
when calling sigaction(2) with sa_mask equal to SA_RESETHAND | SA_NODE-
FER). On BSD, signal() provides reliable semantics. POSIX.1-2001
leaves these aspects of signal() unspecified. See signal(2) for fur-
In order to wait for a signal, BSD and System V both provided a func-
tion named sigpause(3), but this function has a different argument on
the two systems. See sigpause(3) for details.
In versions of glibc before 2.2, sigset() did not unblock sig if disp
was specified as a value other than SIG_HOLD.
In versions of glibc before 2.5, sigset() does not correctly return the
previous disposition of the signal in two cases. First, if disp is
specified as SIG_HOLD, then a successful sigset() always returns
SIG_HOLD. Instead, it should return the previous disposition of the
signal (unless the signal was blocked, in which case SIG_HOLD should be
returned). Second, if the signal is currently blocked, then the return
value of a successful sigset() should be SIG_HOLD. Instead, the previ-
ous disposition of the signal is returned. These problems have been
fixed since glibc 2.5.
kill(2), pause(2), sigaction(2), signal(2), sigprocmask(2), raise(3),
sigpause(3), sigvec(3), feature_test_macros(7), signal(7)
This page is part of release 3.05 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2007-10-16 SIGSET(3)