Provided by: manpages-dev_4.04-2_all bug


       sigprocmask, rt_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

       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


       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 The value specified in how was invalid.


       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.

   C library/kernel differences
       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  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.  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  the  value  sizeof(sigset_t)  (or  the  error  EINVAL
       results).  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 4.04 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