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   7 .TH SIGACTION 2 "Mar 23, 2005"
   8 .SH NAME
   9 sigaction \- detailed signal management
  10 .SH SYNOPSIS
  11 .LP
  12 .nf
  13 #include <signal.h>
  14 
  15 \fBint\fR \fBsigaction\fR(\fBint\fR \fIsig\fR, \fBconst struct sigaction *restrict\fR \fIact\fR,
  16      \fBstruct sigaction *restrict\fR \fIoact\fR);
  17 .fi
  18 
  19 .SH DESCRIPTION
  20 .sp
  21 .LP
  22 The \fBsigaction()\fR function allows the calling process to examine or specify
  23 the action to be taken on delivery of a specific signal. See
  24 \fBsignal.h\fR(3HEAD) for an explanation of general signal concepts.
  25 .sp
  26 .LP
  27 The \fIsig\fR argument specifies the signal and can be assigned any of the
  28 signals specified in \fBsignal.h\fR(3HEAD) except  \fBSIGKILL\fR and
  29 \fBSIGSTOP\fR.
  30 .sp
  31 .LP
  32 If the argument \fIact\fR is not \fINULL\fR, it points to a structure
  33 specifying the new action to be taken when delivering \fIsig\fR. If the
  34 argument \fIoact\fR is not \fINULL\fR, it points to a structure where the
  35 action previously associated with \fIsig\fR is to be stored on return from
  36 \fBsigaction()\fR.
  37 .sp
  38 .LP
  39 The \fBsigaction\fR structure includes the following members:
  40 .sp
  41 .in +2
  42 .nf
  43 void      (*sa_handler)(\|);
  44 void      (*sa_sigaction)(int, siginfo_t *, void *);
  45 sigset_t  sa_mask;
  46 int       sa_flags;
  47 .fi
  48 .in -2
  49 
  50 .sp
  51 .LP
  52 The storage occupied by \fBsa_handler\fR and \fBsa_sigaction\fR may overlap,
  53 and a standard-conforming application (see \fBstandards\fR(5)) must not use
  54 both simultaneously.
  55 .sp
  56 .LP
  57 The \fBsa_handler\fR member identifies the action to be associated with the
  58 specified signal, if the  \fBSA_SIGINFO\fR flag (see below) is cleared in the
  59 \fBsa_flags\fR field of the sigaction structure. It may take any of the values
  60 specified in \fBsignal.h\fR(3HEAD) or that of a user specified signal handler.
  61 If the  \fBSA_SIGINFO\fR flag is set in the \fBsa_flags\fR field, the
  62 \fBsa_sigaction\fR field specifies a signal-catching function.
  63 .sp
  64 .LP
  65 The \fBsa_mask\fR member specifies a set of signals to be blocked while the
  66 signal handler is active. On entry to the signal handler, that set of signals
  67 is added to the set of signals already being blocked when the signal is
  68 delivered. In addition, the signal that caused the handler to be executed will
  69 also be blocked, unless the  \fBSA_NODEFER\fR flag has been specified.
  70 \fBSIGSTOP\fR and  \fBSIGKILL\fR cannot be blocked (the system silently
  71 enforces this restriction).
  72 .sp
  73 .LP
  74 The \fBsa_flags\fR member specifies a set of flags used to modify the delivery
  75 of the signal. It is formed by a logical \fBOR\fR of any of the following
  76 values:
  77 .sp
  78 .ne 2
  79 .na
  80 \fB\fBSA_ONSTACK\fR\fR
  81 .ad
  82 .RS 16n
  83 If set and the signal is caught, and if the thread that is chosen to processes
  84 a delivered signal has an alternate signal stack declared with
  85 \fBsigaltstack\fR(2), then it will process the signal on that stack. Otherwise,
  86 the signal is delivered on the thread's normal stack.
  87 .RE
  88 
  89 .sp
  90 .ne 2
  91 .na
  92 \fB\fBSA_RESETHAND\fR\fR
  93 .ad
  94 .RS 16n
  95 If set and the signal is caught, the disposition of the signal is reset to
  96 \fBSIG_DFL\fR and the signal will not be blocked on entry to the signal handler
  97 (\fBSIGILL\fR, \fBSIGTRAP\fR, and \fBSIGPWR\fR cannot be  automatically reset
  98 when delivered; the system silently enforces this restriction).
  99 .RE
 100 
 101 .sp
 102 .ne 2
 103 .na
 104 \fB\fBSA_NODEFER\fR\fR
 105 .ad
 106 .RS 16n
 107 If set and the signal is caught, the signal will not be automatically blocked
 108 by the kernel while it is being caught.
 109 .RE
 110 
 111 .sp
 112 .ne 2
 113 .na
 114 \fB\fBSA_RESTART\fR\fR
 115 .ad
 116 .RS 16n
 117 If set and the signal is caught, functions that are interrupted by the
 118 execution of this signal's handler are transparently restarted by the system,
 119 namely \fBfcntl\fR(2), \fBioctl\fR(2), \fBwait\fR(3C), \fBwaitid\fR(2), and the
 120 following functions on slow devices like terminals: \fBgetmsg()\fR and
 121 \fBgetpmsg()\fR (see \fBgetmsg\fR(2));  \fBputmsg()\fR and \fBputpmsg()\fR (see
 122 \fBputmsg\fR(2)); \fBpread()\fR, \fBread()\fR, and \fBreadv()\fR (see
 123 \fBread\fR(2)); \fBpwrite()\fR, \fBwrite()\fR, and \fBwritev()\fR (see
 124 \fBwrite\fR(2)); \fBrecv()\fR, \fBrecvfrom()\fR, and \fBrecvmsg()\fR (see
 125 \fBrecv\fR(3SOCKET)); and \fBsend()\fR, \fBsendto()\fR, and \fBsendmsg()\fR
 126 (see \fBsend\fR(3SOCKET)). Otherwise, the function returns an \fBEINTR\fR
 127 error.
 128 .RE
 129 
 130 .sp
 131 .ne 2
 132 .na
 133 \fB\fBSA_SIGINFO\fR\fR
 134 .ad
 135 .RS 16n
 136 If cleared and the signal is caught, \fIsig\fR is passed as the only argument
 137 to the signal-catching function. If set and the signal is caught,  two
 138 additional arguments are passed to the signal-catching function.  If the second
 139 argument is not equal to \fINULL\fR, it points to a \fBsiginfo_t\fR structure
 140 containing the reason why the signal was generated (see
 141 \fBsiginfo.h\fR(3HEAD)); the third argument points to a \fBucontext_t\fR
 142 structure containing the receiving process's context when the signal was
 143 delivered (see \fBucontext.h\fR(3HEAD)).
 144 .RE
 145 
 146 .sp
 147 .ne 2
 148 .na
 149 \fB\fBSA_NOCLDWAIT\fR\fR
 150 .ad
 151 .RS 16n
 152 If set and \fIsig\fR equals  \fBSIGCHLD\fR, the system will not create zombie
 153 processes when children of the calling process exit. If the calling process
 154 subsequently issues a \fBwait\fR(3C), it blocks until all of the calling
 155 process's child processes terminate, and then returns \fB\(mi1\fR with
 156 \fBerrno\fR set to \fBECHILD\fR.
 157 .RE
 158 
 159 .sp
 160 .ne 2
 161 .na
 162 \fB\fBSA_NOCLDSTOP\fR\fR
 163 .ad
 164 .RS 16n
 165 If set and \fIsig\fR equals \fBSIGCHLD\fR, \fBSIGCHLD\fR will not be sent to
 166 the calling process when its child processes stop or continue.
 167 .RE
 168 
 169 .SH RETURN VALUES
 170 .sp
 171 .LP
 172 Upon successful completion, \fB0\fR is returned. Otherwise, \fB\(mi1\fR is
 173 returned, \fBerrno\fR is set to indicate the error, and no new signal handler
 174 is installed.
 175 .SH ERRORS
 176 .sp
 177 .LP
 178 The \fBsigaction()\fR function will fail if:
 179 .sp
 180 .ne 2
 181 .na
 182 \fB\fBEINVAL\fR\fR
 183 .ad
 184 .RS 10n
 185 The value of the \fIsig\fR argument is not a valid signal number or is equal to
 186 \fBSIGKILL\fR or \fBSIGSTOP\fR. In addition, if in a multithreaded process, it
 187 is equal to \fBSIGWAITING\fR, \fBSIGCANCEL\fR, or \fBSIGLWP\fR.
 188 .RE
 189 
 190 .SH ATTRIBUTES
 191 .sp
 192 .LP
 193 See \fBattributes\fR(5) for descriptions of the following attributes:
 194 .sp
 195 
 196 .sp
 197 .TS
 198 box;
 199 c | c
 200 l | l .
 201 ATTRIBUTE TYPE  ATTRIBUTE VALUE
 202 _
 203 Interface Stability     Committed
 204 _
 205 MT-Level        Async-Signal-Safe
 206 _
 207 Standard        See \fBstandards\fR(5).
 208 .TE
 209 
 210 .SH SEE ALSO
 211 .sp
 212 .LP
 213 \fBkill\fR(1), \fBIntro\fR(2), \fBexit\fR(2), \fBfcntl\fR(2), \fBgetmsg\fR(2),
 214 \fBioctl\fR(2), \fBkill\fR(2), \fBpause\fR(2), \fBputmsg\fR(2), \fBread\fR(2),
 215 \fBsigaltstack\fR(2), \fBsigprocmask\fR(2), \fBsigsend\fR(2),
 216 \fBsigsuspend\fR(2), \fBwaitid\fR(2), \fBwrite\fR(2), \fBrecv\fR(3SOCKET),
 217 \fBsend\fR(3SOCKET), \fBsiginfo.h\fR(3HEAD), \fBsignal\fR(3C),
 218 \fBsignal.h\fR(3HEAD), \fBsigsetops\fR(3C), \fBucontext.h\fR(3HEAD),
 219 \fBwait\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5)
 220 .SH NOTES
 221 .sp
 222 .LP
 223 The handler routine can be declared:
 224 .sp
 225 .in +2
 226 .nf
 227 void handler (int \fIsig\fR, siginfo_t *\fIsip\fR, ucontext_t *\fIucp\fR);
 228 .fi
 229 .in -2
 230 
 231 .sp
 232 .LP
 233 The \fIsig\fR argument is the signal number. The \fIsip\fR argument is a
 234 pointer (to space on the stack) to a \fBsiginfo_t\fR structure, which provides
 235 additional detail about the delivery of the signal. The \fIucp\fR argument is a
 236 pointer (again to space on the stack) to a \fBucontext_t\fR structure (defined
 237 in <\fBsys/ucontext.h\fR>) which contains the context from before the signal.
 238 It is not recommended that \fIucp\fR be used by the handler to restore the
 239 context from before the signal delivery.