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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |VERSIONS |STANDARDS |HISTORY |NOTES |SEE ALSO |COLOPHON | |
sigprocmask(2) System Calls Manualsigprocmask(2)sigprocmask, rt_sigprocmask - examine and change blocked signals
Standard C library (libc,-lc)
#include <signal.h> /* Prototype for the glibc wrapper function */int sigprocmask(inthow, const sigset_t *_Nullable restrictset,sigset_t *_Nullable restrictoldset);#include <signal.h>/* Definition ofSIG_*constants */#include <sys/syscall.h>/* Definition ofSYS_*constants */#include <unistd.h> /* Prototype for the underlying system call */int syscall(SYS_rt_sigprocmask, inthow,const kernel_sigset_t *_Nullableset,kernel_sigset_t *_Nullableoldset,size_tsigsetsize); /* Prototype for the legacy system call */[[deprecated]] int syscall(SYS_sigprocmask, inthow,const old_kernel_sigset_t *_Nullableset,old_kernel_sigset_t *_Nullableoldset); Feature Test Macro Requirements for glibc (seefeature_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 alsosignal(7) for more details). The behavior of the call is dependent on the value ofhow, as follows.SIG_BLOCK The set of blocked signals is the union of the current set and theset argument.SIG_UNBLOCK The signals inset 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 argumentset. Ifoldset is non-NULL, the previous value of the signal mask is stored inoldset. Ifset is NULL, then the signal mask is unchanged (i.e.,how is ignored), but the current value of the signal mask is nevertheless returned inoldset (if it is not NULL). A set of functions for modifying and inspecting variables of typesigset_t ("signal sets") is described insigsetops(3). The use ofsigprocmask() is unspecified in a multithreaded process; seepthread_sigmask(3).sigprocmask() returns 0 on success. On failure, -1 is returned anderrno is set to indicate the error.
EFAULTTheset oroldset argument points outside the process's allocated address space.EINVALEither the value specified inhow was invalid or the kernel does not support the size passed insigsetsize.
C library/kernel differences The kernel's definition ofsigset_t differs in size from that used by the C library. In this manual page, the former is referred to askernel_sigset_t (it is nevertheless namedsigset_t in the kernel sources). The glibc wrapper function forsigprocmask() silently ignores attempts to block the two real-time signals that are used internally by the NPTL threading implementation. Seenptl(7) for details. The original Linux system call was namedsigprocmask(). However, with the addition of real-time signals in Linux 2.2, the fixed- size, 32-bitsigset_t (referred to asold_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 enlargedsigset_t type (referred to askernel_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 inset andoldset. This argument is currently required to have a fixed architecture specific value (equal tosizeof(kernel_sigset_t)). The glibcsigprocmask() wrapper function hides these details from us, transparently callingrt_sigprocmask() when the kernel provides it.
POSIX.1-2008.
POSIX.1-2001.
It is not possible to blockSIGKILLorSIGSTOP. Attempts to do so are silently ignored. Each of the threads in a process has its own signal mask. A child created viafork(2) inherits a copy of its parent's signal mask; the signal mask is preserved acrossexecve(2). IfSIGBUS,SIGFPE,SIGILL, orSIGSEGVare generated while they are blocked, the result is undefined, unless the signal was generated bykill(2),sigqueue(3), orraise(3). Seesigsetops(3) for details on manipulating signal sets. Note that it is permissible (although not very useful) to specify bothset andoldset as NULL.
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 theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17sigprocmask(2)Pages that refer to this page:env(1), clone(2), io_uring_enter2(2), io_uring_enter(2), poll(2), ptrace(2), rt_sigqueueinfo(2), seccomp(2), select(2), select_tut(2), sgetmask(2), sigaction(2), signal(2), signalfd(2), sigpending(2), sigsuspend(2), sigwaitinfo(2), syscalls(2), getcontext(3), makecontext(3), posix_spawn(3), pthread_attr_setsigmask_np(3), pthread_sigmask(3), sd_event_add_child(3), sd_event_add_signal(3), sigpause(3), sigset(3), sigsetops(3), sigvec(3), sigwait(3), system(3), systemd.exec(5), nptl(7), signal(7), signal-safety(7), system_data_types(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |