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)