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28 .\" @(#)sigvec.2 8.2 (Berkeley) 4/19/94
29 .\" $FreeBSD: src/lib/libc/compat-43/sigvec.2,v 1.9.2.8 2003/03/15 15:11:05 trhodes Exp $
30 .\" $DragonFly: src/lib/libc/compat-43/sigvec.2,v 1.4 2006/05/26 19:39:36 swildner Exp $
37 .Nd software signal facilities
50 .Fn sigvec "int sig" "struct sigvec *vec" "struct sigvec *ovec"
53 This interface is made obsolete by
57 The system defines a set of signals that may be delivered to a process.
58 Signal delivery resembles the occurrence of a hardware interrupt:
59 the signal is blocked from further occurrence, the current process
60 context is saved, and a new one is built. A process may specify a
62 to which a signal is delivered, or specify that a signal is to be
66 A process may also specify that a default action is to be taken
67 by the system when a signal occurs.
68 Normally, signal handlers execute on the current stack
69 of the process. This may be changed, on a per-handler basis,
70 so that signals are taken on a special
73 All signals have the same
75 Signal routines execute with the signal that caused their
78 but other signals may yet occur.
81 defines the set of signals currently blocked from delivery
82 to a process. The signal mask for a process is initialized
83 from that of its parent (normally 0). It
88 call, or when a signal is delivered to the process.
91 condition arises for a process, the signal is added to a set of
92 signals pending for the process. If the signal is not currently
94 by the process then it is delivered to the process. When a signal
95 is delivered, the current state of the process is saved,
96 a new signal mask is calculated (as described below),
97 and the signal handler is invoked. The call to the handler
98 is arranged so that if the signal handling routine returns
99 normally the process will resume execution in the context
100 from before the signal's delivery.
101 If the process wishes to resume in a different context, then it
102 must arrange to restore the previous context itself.
104 When a signal is delivered to a process a new signal mask is
105 installed for the duration of the process' signal handler
111 This mask is formed by taking the current signal mask,
112 adding the signal to be delivered, and
114 in the signal mask associated with the handler to be invoked.
119 assigns a handler for a specific signal. If
122 specifies a handler routine and mask
123 to be used when delivering the specified signal.
128 the system will deliver the signal to the process on a
134 is non-zero, the previous handling information for the signal
135 is returned to the user.
137 The following is a list of all signals
138 with names as in the include file
140 .Bl -column SIGVTALARMXX "create core imagexxx"
141 .It Sy "NAME Default Action Description"
142 .It Dv SIGHUP No " terminate process" " terminal line hangup"
143 .It Dv SIGINT No " terminate process" " interrupt program"
144 .It Dv SIGQUIT No " create core image" " quit program"
145 .It Dv SIGILL No " create core image" " illegal instruction"
146 .It Dv SIGTRAP No " create core image" " trace trap"
147 .It Dv SIGABRT No " create core image" Ta Xr abort 3
150 .It Dv SIGEMT No " create core image" " emulate instruction executed"
151 .It Dv SIGFPE No " create core image" " floating-point exception"
152 .It Dv SIGKILL No " terminate process" " kill program"
153 .It Dv SIGBUS No " create core image" " bus error"
154 .It Dv SIGSEGV No " create core image" " segmentation violation"
155 .It Dv SIGSYS No " create core image" " non-existent system call invoked"
156 .It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
157 .It Dv SIGALRM No " terminate process" " real-time timer expired"
158 .It Dv SIGTERM No " terminate process" " software termination signal"
159 .It Dv SIGURG No " discard signal" " urgent condition present on socket"
160 .It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
161 .It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
162 .It Dv SIGCONT No " discard signal" " continue after stop"
163 .It Dv SIGCHLD No " discard signal" " child status has changed"
164 .It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
165 .It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
166 .It Dv SIGIO No " discard signal" Tn " I/O"
167 is possible on a descriptor (see
169 .It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
171 .It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
173 .It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
175 .It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
177 .It Dv SIGWINCH No " discard signal" " Window size change"
178 .It Dv SIGINFO No " discard signal" " status request from keyboard"
179 .It Dv SIGUSR1 No " terminate process" " User defined signal 1"
180 .It Dv SIGUSR2 No " terminate process" " User defined signal 2"
183 Once a signal handler is installed, it remains installed
189 A signal-specific default action may be reset by
194 The defaults are process termination, possibly with core dump;
195 no action; stopping the process; or continuing the process.
196 See the above signal list for each signal's default action.
201 current and pending instances
202 of the signal are ignored and discarded.
204 If a signal is caught during the system calls listed below,
205 the call is normally restarted.
206 The call can be forced to terminate prematurely with an
208 error return by setting the
212 The affected system calls include
220 on a communications channel or a slow device (such as a terminal,
221 but not a regular file)
226 However, calls that have already committed are not restarted,
227 but instead return a partial success (for example, a short read count).
233 all signals, the signal mask, the signal stack,
234 and the restart/interrupt flags are inherited by the child.
238 system call reinstates the default
239 action for all signals which were caught and
240 resets all signals to be caught on the user stack.
241 Ignored signals remain ignored;
242 the signal mask remains the same;
243 signals that interrupt system calls continue to do so.
245 The mask specified in
247 is not allowed to block
251 This is done silently by the system.
255 flag is not available in
257 hence it should not be used if backward compatibility is needed.
263 The handler routine can be declared:
264 .Bd -literal -offset indent
265 void handler(sig, code, scp)
267 struct sigcontext *scp;
272 is the signal number, into which the hardware faults and traps are
273 mapped as defined below.
278 as given below or, for compatibility mode faults, the code provided by
279 the hardware (Compatibility mode faults are distinguished from the
290 structure (defined in
292 used to restore the context from before the signal.
297 will fail and no new signal handler will be installed if one
298 of the following occurs:
305 points to memory that is not a valid part of the process
311 is not a valid signal number.
313 An attempt is made to ignore or supply a handler for
335 This manual page is still confusing.