sigprocmask(2)



SIGPROCMASK(2)             Linux Programmer's Manual            SIGPROCMASK(2)

NAME
       sigprocmask, rt_sigprocmask - examine and change blocked signals

SYNOPSIS
       #include <signal.h>

       int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

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

       sigprocmask(): _POSIX_C_SOURCE

DESCRIPTION
       sigprocmask()  is  used  to  fetch and/or change the signal mask of the
       calling thread.  The signal mask is the set of signals  whose  delivery
       is  currently  blocked  for  the  caller  (see  also signal(7) for more
       details).

       The behavior of the call is dependent on the value of how, as follows.

       SIG_BLOCK
              The set of blocked signals is the union of the current  set  and
              the set argument.

       SIG_UNBLOCK
              The  signals  in set are removed from the current set of blocked
              signals.  It is permissible to attempt to unblock a signal which
              is not blocked.

       SIG_SETMASK
              The set of blocked signals is set to the argument set.

       If  oldset is non-NULL, the previous value of the signal mask is stored
       in oldset.

       If set is NULL, then  the  signal  mask  is  unchanged  (i.e.,  how  is
       ignored),  but  the  current  value  of the signal mask is nevertheless
       returned in oldset (if it is not NULL).

       A set of functions for  modifying  and  inspecting  variables  of  type
       sigset_t ("signal sets") is described in sigsetops(3).

       The use of sigprocmask() is unspecified in a multithreaded process; see
       pthread_sigmask(3).

RETURN VALUE
       sigprocmask() returns 0 on success and -1 on error.  In the event of an
       error, errno is set to indicate the cause.

ERRORS
       EFAULT The  set  or  oldset argument points outside the process's allo-
              cated address space.

       EINVAL The value specified in how was invalid.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       It is not possible to block SIGKILL or SIGSTOP.  Attempts to do so  are
       silently ignored.

       Each of the threads in a process has its own signal mask.

       A  child  created  via  fork(2)  inherits a copy of its parent's signal
       mask; the signal mask is preserved across execve(2).

       If SIGBUS, SIGFPE, SIGILL, or SIGSEGV  are  generated  while  they  are
       blocked,  the  result  is undefined, unless the signal was generated by
       kill(2), sigqueue(3), or raise(3).

       See sigsetops(3) for details on manipulating signal sets.

   C library/kernel differences
       The glibc wrapper function for sigprocmask() silently ignores  attempts
       to block the two real-time signals that are used internally by the NPTL
       threading implementation.  See nptl(7) for details.

       The original Linux system call was named sigprocmask().  However,  with
       the  addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
       sigset_t type supported by that system call was no longer fit for  pur-
       pose.   Consequently, a new system call, rt_sigprocmask(), was added to
       support an enlarged sigset_t type.  The new system call takes a  fourth
       argument,  size_t  sigsetsize, which specifies the size in bytes of the
       signal sets in set and oldset.  This argument is currently required  to
       have  the  value  sizeof(sigset_t)  (or the error EINVAL results).  The
       glibc sigprocmask() wrapper  function  hides  these  details  from  us,
       transparently calling rt_sigprocmask() when the kernel provides it.

SEE ALSO
       kill(2),  pause(2),  sigaction(2),  signal(2),  sigpending(2),  sigsus-
       pend(2), pthread_sigmask(3), sigqueue(3), sigsetops(3), signal(7)

COLOPHON
       This page is part of release 4.06 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux                             2016-03-15                    SIGPROCMASK(2)

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