NAME

       sigprocmask, rt_sigprocmask - examine and change blocked signals

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <signal.h>

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

       #include <signal.h>           /* Definition of SIG_* constants */
       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

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

       /* Prototype for the legacy system call */
       [[deprecated]] int syscall(SYS_sigprocmask, int how,
                                  const old_kernel_sigset_t *_Nullable set,
                                  old_kernel_sigset_t *_Nullable 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.  On failure, -1 is returned and errno is set to indicate the error.

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.

VERSIONS

   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.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.

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.

SEE ALSO

       kill(2),   pause(2),   sigaction(2),   signal(2),   sigpending(2),   sigsuspend(2),   pthread_sigmask(3),
       sigqueue(3), sigsetops(3), signal(7)