Manpages - sigset.3

sigset, sighold, sigrelse, sigignore - System V signal API

  #include <signal.h>

  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);

Feature Test Macro Requirements for glibc (see *feature_test_macros*(7)):

*sigset*(), *sighold*(), *sigrelse*(), *sigignore*():

      _XOPEN_SOURCE >= 500

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 This API is obsolete: new applications should use the POSIX signal API (*sigaction*(2), *sigprocmask*(2), etc.)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:

SIG_DFL

Reset the disposition of sig to the default.

SIG_IGN

Ignore sig.

SIG_HOLD

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 mask.

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 success; on error, these functions return -1 and set errno to indicate the error.

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).

For an explanation of the terms used in this section, see *attributes*(7).

SVr4, POSIX.1-2001, POSIX.1-2008. These functions are obsolete: do not use them in new programs. POSIX.1-2008 marks *sighold*(), *sigignore*(), *sigpause*(3), *sigrelse*(), and *sigset*() as obsolete, recommending the use of *sigaction*(2), *sigprocmask*(2), *pthread_sigmask*(3), and *sigsuspend*(2) instead.

These functions appeared in glibc version 2.1.

The sighandler_t type is a GNU extension; it is used on this page only 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_NODEFER). On BSD, *signal*() provides reliable semantics. POSIX.1-2001 leaves these aspects of *signal*() unspecified. See *signal*(2) for further details.

In order to wait for a signal, BSD and System V both provided a function 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 previous 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), *signal*(7)

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