man2/sigprocmask.2

   1 .\" Copyright (c) 2005 Michael Kerrisk
   2 .\" based on earlier work by faith@cs.unc.edu and
   3 .\" Mike Battersby <mib@deakin.edu.au>
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  27 .\" 2005-09-15, mtk, Created new page by splitting off from sigaction.2
  28 .\"
  29 .TH SIGPROCMASK 2 2015-07-23 "Linux" "Linux Programmer's Manual"
  30 .SH NAME
  31 sigprocmask, rt_sigprocmask \- examine and change blocked signals
  32 .SH SYNOPSIS
  33 .B #include <signal.h>
  34 .sp
  35 .BI "int sigprocmask(int " how ", const sigset_t *" set ,
  36 .BI "sigset_t *" oldset );
  37 .sp
  38 .in -4n
  39 Feature Test Macro Requirements for glibc (see
  40 .BR feature_test_macros (7)):
  41 .in
  42 .sp
  43 .ad l
  44 .BR sigprocmask ():
  45 _POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _POSIX_SOURCE
  46 .ad b
  47 .SH DESCRIPTION
  48 .BR sigprocmask ()
  49 is used to fetch and/or change the signal mask of the calling thread.
  50 The signal mask is the set of signals whose delivery is currently
  51 blocked for the caller
  52 (see also
  53 .BR signal (7)
  54 for more details).
  55
  56 The behavior of the call is dependent on the value of
  57 .IR how ,
  58 as follows.
  59 .TP
  60 .B SIG_BLOCK
  61 The set of blocked signals is the union of the current set and the
  62 .I set
  63 argument.
  64 .TP
  65 .B SIG_UNBLOCK
  66 The signals in
  67 .I set
  68 are removed from the current set of blocked signals.
  69 It is permissible to attempt to unblock a signal which is not blocked.
  70 .TP
  71 .B SIG_SETMASK
  72 The set of blocked signals is set to the argument
  73 .IR set .
  74 .PP
  75 If
  76 .I oldset
  77 is non-NULL, the previous value of the signal mask is stored in
  78 .IR oldset .
  79
  80 If
  81 .I set
  82 is NULL, then the signal mask is unchanged (i.e.,
  83 .I how
  84 is ignored),
  85 but the current value of the signal mask is nevertheless returned in
  86 .I oldset
  87 (if it is not NULL).
  88
  89 The use of
  90 .BR sigprocmask ()
  91 is unspecified in a multithreaded process; see
  92 .BR pthread_sigmask (3).
  93 .SH RETURN VALUE
  94 .BR sigprocmask ()
  95 returns 0 on success and \-1 on error.
  96 In the event of an error,
  97 .I errno
  98 is set to indicate the cause.
  99 .SH ERRORS
 100 .TP
 101 .B EFAULT
 102 The
 103 .I set
 104 or
 105 .I oldset
 106 argument points outside the process's allocated address space.
 107 .TP
 108 .B EINVAL
 109 The value specified in
 110 .I how
 111 was invalid.
 112 .SH CONFORMING TO
 113 POSIX.1-2001, POSIX.1-2008.
 114 .SH NOTES
 115 It is not possible to block
 116 .BR SIGKILL " or " SIGSTOP .
 117 Attempts to do so are silently ignored.
 118
 119 Each of the threads in a process has its own signal mask.
 120
 121 A child created via
 122 .BR fork (2)
 123 inherits a copy of its parent's signal mask;
 124 the signal mask is preserved across
 125 .BR execve (2).
 126
 127 If
 128 .BR SIGBUS ,
 129 .BR SIGFPE ,
 130 .BR SIGILL ,
 131 or
 132 .B SIGSEGV
 133 are generated
 134 while they are blocked, the result is undefined,
 135 unless the signal was generated by
 136 .BR kill (2),
 137 .BR sigqueue (3),
 138 or
 139 .BR raise (3).
 140 .PP
 141 See
 142 .BR sigsetops (3)
 143 for details on manipulating signal sets.
 144 .\"
 145 .SS C library/kernel differences
 146 The glibc wrapper function for
 147 .BR sigprocmask ()
 148 silently ignores attempts to block the two real-time signals that
 149 are used internally by the NPTL threading implementation.
 150 See
 151 .BR nptl (7)
 152 for details.
 153
 154 The original Linux system call was named
 155 .BR sigprocmask ().
 156 However, with the addition of real-time signals in Linux 2.2,
 157 the fixed-size, 32-bit
 158 .IR sigset_t
 159 type supported by that system call was no longer fit for purpose.
 160 Consequently, a new system call,
 161 .BR rt_sigprocmask (),
 162 was added to support an enlarged
 163 .IR sigset_t
 164 type.
 165 The new system call takes a fourth argument,
 166 .IR "size_t sigsetsize" ,
 167 which specifies the size in bytes of the signal sets in
 168 .IR set
 169 and
 170 .IR oldset .
 171 This argument is currently required to have the value
 172 .IR sizeof(sigset_t)
 173 (or the error
 174 .B EINVAL
 175 results).
 176 The glibc
 177 .BR sigprocmask ()
 178 wrapper function hides these details from us, transparently calling
 179 .BR rt_sigprocmask ()
 180 when the kernel provides it.
 181 .\"
 182 .SH SEE ALSO
 183 .BR kill (2),
 184 .BR pause (2),
 185 .BR sigaction (2),
 186 .BR signal (2),
 187 .BR sigpending (2),
 188 .BR sigsuspend (2),
 189 .BR pthread_sigmask (3),
 190 .BR sigqueue (3),
 191 .BR sigsetops (3),
 192 .BR signal (7)