1SIGPROCMASK(2) Linux Programmer's Manual SIGPROCMASK(2)
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6 sigprocmask, rt_sigprocmask - examine and change blocked signals
7
9 #include <signal.h>
10 /* Prototype for the glibc wrapper function */
12 int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
13 /* Prototype for the underlying system call */
15 int rt_sigprocmask(int how, const kernel_sigset_t *set,
16 kernel_sigset_t *oldset, size_t sigsetsize);
17 /* Prototype for the legacy system call (deprecated) */
19 int sigprocmask(int how, const old_kernel_sigset_t *set,
20 old_kernel_sigset_t *oldset);
21 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
23 sigprocmask(): _POSIX_C_SOURCE
25
27 sigprocmask() is used to fetch and/or change the signal mask of the
28 calling thread. The signal mask is the set of signals whose delivery
29 is currently blocked for the caller (see also signal(7) for more
30 details).
31 The behavior of the call is dependent on the value of how, as follows.
33 SIG_BLOCK
35 The set of blocked signals is the union of the current set and
36 the set argument.
37 SIG_UNBLOCK
39 The signals in set are removed from the current set of blocked
40 signals. It is permissible to attempt to unblock a signal which
41 is not blocked.
42 SIG_SETMASK
44 The set of blocked signals is set to the argument set.
45 If oldset is non-NULL, the previous value of the signal mask is stored
47 in oldset.
48 If set is NULL, then the signal mask is unchanged (i.e., how is
50 ignored), but the current value of the signal mask is nevertheless
51 returned in oldset (if it is not NULL).
52 A set of functions for modifying and inspecting variables of type
54 sigset_t ("signal sets") is described in sigsetops(3).
55 The use of sigprocmask() is unspecified in a multithreaded process; see
57 pthread_sigmask(3).
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60 sigprocmask() returns 0 on success and -1 on error. In the event of an
61 error, errno is set to indicate the cause.
62
64 EFAULT The set or oldset argument points outside the process's allo‐
65 cated address space.
66 EINVAL Either the value specified in how was invalid or the kernel does
68 not support the size passed in sigsetsize.
69
71 POSIX.1-2001, POSIX.1-2008.
72
74 It is not possible to block SIGKILL or SIGSTOP. Attempts to do so are
75 silently ignored.
76 Each of the threads in a process has its own signal mask.
78 A child created via fork(2) inherits a copy of its parent's signal
80 mask; the signal mask is preserved across execve(2).
81 If SIGBUS, SIGFPE, SIGILL, or SIGSEGV are generated while they are
83 blocked, the result is undefined, unless the signal was generated by
84 kill(2), sigqueue(3), or raise(3).
85 See sigsetops(3) for details on manipulating signal sets.
87 Note that it is permissible (although not very useful) to specify both
89 set and oldset as NULL.
90 C library/kernel differences
92 The kernel's definition of sigset_t differs in size from that used by
93 the C library. In this manual page, the former is referred to as ker‐
94 nel_sigset_t (it is nevertheless named sigset_t in the kernel sources).
95 The glibc wrapper function for sigprocmask() silently ignores attempts
97 to block the two real-time signals that are used internally by the NPTL
98 threading implementation. See nptl(7) for details.
99 The original Linux system call was named sigprocmask(). However, with
101 the addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
102 sigset_t (referred to as old_kernel_sigset_t in this manual page) type
103 supported by that system call was no longer fit for purpose. Conse‐
104 quently, a new system call, rt_sigprocmask(), was added to support an
105 enlarged sigset_t type (referred to as kernel_sigset_t in this manual
106 page). The new system call takes a fourth argument, size_t sigsetsize,
107 which specifies the size in bytes of the signal sets in set and oldset.
108 This argument is currently required to have a fixed architecture spe‐
109 cific value (equal to sizeof(kernel_sigset_t)).
110 The glibc sigprocmask() wrapper function hides these details from us,
112 transparently calling rt_sigprocmask() when the kernel provides it.
113
115 kill(2), pause(2), sigaction(2), signal(2), sigpending(2), sigsus‐
116 pend(2), pthread_sigmask(3), sigqueue(3), sigsetops(3), signal(7)
117
119 This page is part of release 5.04 of the Linux man-pages project. A
120 description of the project, information about reporting bugs, and the
121 latest version of this page, can be found at
122 https://www.kernel.org/doc/man-pages/.
123Linux 2017-09-15 SIGPROCMASK(2)