sigsetmask(3) — Linux manual page


SIGVEC(3)                 Linux Programmer's Manual                SIGVEC(3)

NAME         top

       sigvec, sigblock, sigsetmask, siggetmask, sigmask - BSD signal API

SYNOPSIS         top

       #include <signal.h>

       int sigvec(int sig, const struct sigvec *vec, struct sigvec *ovec);

       int sigmask(int signum);

       int sigblock(int mask);

       int sigsetmask(int mask);

       int siggetmask(void);

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

       All functions shown above:
           Since glibc 2.19:
           Glibc 2.19 and earlier:

DESCRIPTION         top

       These functions are provided in glibc as a compatibility interface
       for programs that make use of the historical BSD signal API.  This
       API is obsolete: new applications should use the POSIX signal API
       (sigaction(2), sigprocmask(2), etc.).

       The sigvec() function sets and/or gets the disposition of the signal
       sig (like the POSIX sigaction(2)).  If vec is not NULL, it points to
       a sigvec structure that defines the new disposition for sig.  If ovec
       is not NULL, it points to a sigvec structure that is used to return
       the previous disposition of sig.  To obtain the current disposition
       of sig without changing it, specify NULL for vec, and a non-null
       pointer for ovec.

       The dispositions for SIGKILL and SIGSTOP cannot be changed.

       The sigvec structure has the following form:

           struct sigvec {
               void (*sv_handler)(int); /* Signal disposition */
               int    sv_mask;          /* Signals to be blocked in handler */
               int    sv_flags;         /* Flags */

       The sv_handler field specifies the disposition of the signal, and is
       either: the address of a signal handler function; SIG_DFL, meaning
       the default disposition applies for the signal; or SIG_IGN, meaning
       that the signal is ignored.

       If sv_handler specifies the address of a signal handler, then sv_mask
       specifies a mask of signals that are to be blocked while the handler
       is executing.  In addition, the signal for which the handler is in‐
       voked is also blocked.  Attempts to block SIGKILL or SIGSTOP are
       silently ignored.

       If sv_handler specifies the address of a signal handler, then the
       sv_flags field specifies flags controlling what happens when the han‐
       dler is called.  This field may contain zero or more of the following

              If the signal handler interrupts a blocking system call, then
              upon return from the handler the system call s not be
              restarted: instead it fails with the error EINTR.  If this
              flag is not specified, then system calls are restarted by de‐

              Reset the disposition of the signal to the default before
              calling the signal handler.  If this flag is not specified,
              then the handler remains established until explicitly removed
              by a later call to sigvec() or until the process performs an

              Handle the signal on the alternate signal stack (historically
              established under BSD using the obsolete sigstack() function;
              the POSIX replacement is sigaltstack(2)).

       The sigmask() macro constructs and returns a "signal mask" for
       signum.  For example, we can initialize the vec.sv_mask field given
       to sigvec() using code such as the following:

           vec.sv_mask = sigmask(SIGQUIT) | sigmask(SIGABRT);
                       /* Block SIGQUIT and SIGABRT during
                          handler execution */

       The sigblock() function adds the signals in mask to the process's
       signal mask (like POSIX sigprocmask(SIG_BLOCK)), and returns the
       process's previous signal mask.  Attempts to block SIGKILL or SIGSTOP
       are silently ignored.

       The sigsetmask() function sets the process's signal mask to the value
       given in mask (like POSIX sigprocmask(SIG_SETMASK)), and returns the
       process's previous signal mask.

       The siggetmask() function returns the process's current signal mask.
       This call is equivalent to sigblock(0).

RETURN VALUE         top

       The sigvec() function returns 0 on success; on error, it returns -1
       and sets errno to indicate the error.

       The sigblock() and sigsetmask() functions return the previous signal

       The sigmask() macro returns the signal mask for signum.

ERRORS         top

       See the ERRORS under sigaction(2) and sigprocmask(2).

VERSIONS         top

       Starting with version 2.21, the GNU C library no longer exports the
       sigvec() function as part of the ABI.  (To ensure backward
       compatibility, the glibc symbol versioning scheme continues to export
       the interface to binaries linked against older versions of the

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                        Attribute     Value   │
       │sigvec(), sigmask(), sigblock(), │ Thread safety │ MT-Safe │
       │sigsetmask(), siggetmask()       │               │         │

CONFORMING TO         top

       All of these functions were in 4.3BSD, except siggetmask(), whose
       origin is unclear.  These functions are obsolete: do not use them in
       new programs.

NOTES         top

       On 4.3BSD, the signal() function provided reliable semantics (as when
       calling sigvec() with vec.sv_mask equal to 0).  On System V, signal()
       provides unreliable semantics.  POSIX.1 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.

SEE ALSO         top

       kill(2), pause(2), sigaction(2), signal(2), sigprocmask(2), raise(3),
       sigpause(3), sigset(3), signal(7)

COLOPHON         top

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       latest version of this page, can be found at

Linux                            2020-08-13                        SIGVEC(3)