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 details).

       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

       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 allocated
              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
       kernel_sigset_t (it is nevertheless named sigset_t in the kernel

       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.

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

       This page is part of release 5.10 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)