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

       sigprocmask - examine and change blocked signals

       #include <signal.h>

       int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sigprocmask(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_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 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).

       The use of sigprocmask() is unspecified in a multithreaded process; see pthread_sigmask(3).

       sigprocmask() returns 0 on success and -1 on error.

       EINVAL The value specified in how was invalid.


       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

       If SIGBUS, SIGFPE, SIGILL, or SIGSEGV are generated while they are blocked, the result is undefined, unless the
       signal was generated by the kill(2), sigqueue(2), or raise(3).

       See sigsetops(3) for details on manipulating signal sets.

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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2008-10-17                    SIGPROCMASK(2)