NAME

       sigprocmask, rt_sigprocmask - examine and change blocked signals

SYNOPSIS

       #include <signal.h>

       /* Prototype for the glibc wrapper function */
       int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

       /* Prototype for the underlying system call */
       int rt_sigprocmask(int how, const kernel_sigset_t *set,
                          kernel_sigset_t *oldset, size_t sigsetsize);

       /* Prototype for the legacy system call (deprecated) */
       int sigprocmask(int how, const old_kernel_sigset_t *set,
                       old_kernel_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 allocated address space.

       EINVAL Either  the  value  specified in how was invalid or the kernel does not support the size passed in
              sigsetsize.

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.

       Note that it is permissible (although not very useful) to specify both set and oldset as NULL.

   C library/kernel differences
       The kernel's definition of sigset_t differs in size from that used by the  C  library.   In  this  manual
       page,  the  former  is  referred  to  as kernel_sigset_t (it is nevertheless named sigset_t in the kernel
       sources).

       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 (referred to as old_kernel_sigset_t in  this  manual  page)
       type  supported  by  that  system  call  was no longer fit for purpose.  Consequently, a new system call,
       rt_sigprocmask(), was added to support an enlarged sigset_t type (referred to as kernel_sigset_t in  this
       manual  page).   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  a  fixed
       architecture specific value (equal to sizeof(kernel_sigset_t)).

       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),   sigsuspend(2),   pthread_sigmask(3),
       sigqueue(3), sigsetops(3), signal(7)

COLOPHON

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       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.