sigprocmask, rt_sigprocmask - examine and change blocked signals

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).

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.

       Standard C library (libc, -lc)

       sigprocmask, rt_sigprocmask - examine and change blocked signals

       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.

sigprocmask() returns 0 on success.  On failure, -1 is returned and errno is set to indicate the error.

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

Linux man-pages 6.9.1                              2024-05-02                                     sigprocmask(2)

       POSIX.1-2008.

#include<signal.h>

       /* Prototype for the glibc wrapper function */
       intsigprocmask(inthow,constsigset_t*_Nullablerestrictset,sigset_t*_Nullablerestrictoldset);#include<signal.h>           /* Definition of SIG_* constants */
       #include<sys/syscall.h>      /* Definition of SYS_* constants */
       #include<unistd.h>

       /* Prototype for the underlying system call */
       intsyscall(SYS_rt_sigprocmask,inthow,constkernel_sigset_t*_Nullableset,kernel_sigset_t*_Nullableoldset,size_tsigsetsize);

       /* Prototype for the legacy system call */
       [[deprecated]]intsyscall(SYS_sigprocmask,inthow,constold_kernel_sigset_t*_Nullableset,old_kernel_sigset_t*_Nullableoldset);

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

       sigprocmask():
           _POSIX_C_SOURCE

Clibrary/kerneldifferences
       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_tsigsetsize, 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.