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


     sigprocmask, rt_sigprocmask - examine and change blocked signals


     #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


     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
     The behavior of the call is dependent on the value of how, as  follows.
            The  set  of blocked signals is the union of the current set and
            the set argument.
            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.
            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


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


     EFAULT The set or oldset argument points outside  the  process's  allo-
            cated address space.
     EINVAL Either the value specified in how was invalid or the kernel does
            not support the size passed in sigsetsize.


     POSIX.1-2001, POSIX.1-2008.


     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  ker-
     nel_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.  Conse-
     quently, 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  spe-
     cific 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.


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


     This  page  is  part of release 4.16 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

Linux 2017-09-15 SIGPROCMASK(2)

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