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28 .\" @(#)sigvec.2 8.2 (Berkeley) 4/19/94
36 .Nd software signal facilities
49 .Fn sigvec "int sig" "struct sigvec *vec" "struct sigvec *ovec"
52 This interface is made obsolete by
56 The system defines a set of signals that may be delivered to a process.
57 Signal delivery resembles the occurrence of a hardware interrupt:
58 the signal is blocked from further occurrence, the current process
59 context is saved, and a new one is built.
60 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
70 This may be changed, on a per-handler basis,
71 so that signals are taken on a special
74 All signals have the same
76 Signal routines execute with the signal that caused their
79 but other signals may yet occur.
82 defines the set of signals currently blocked from delivery
84 The signal mask for a process is initialized
85 from that of its parent (normally 0).
91 call, or when a signal is delivered to the process.
94 condition arises for a process, the signal is added to a set of
95 signals pending for the process.
96 If the signal is not currently
98 by the process then it is delivered to the process.
100 is delivered, the current state of the process is saved,
101 a new signal mask is calculated (as described below),
102 and the signal handler is invoked.
103 The call to the handler
104 is arranged so that if the signal handling routine returns
105 normally the process will resume execution in the context
106 from before the signal's delivery.
107 If the process wishes to resume in a different context, then it
108 must arrange to restore the previous context itself.
110 When a signal is delivered to a process a new signal mask is
111 installed for the duration of the process' signal handler
117 This mask is formed by taking the current signal mask,
118 adding the signal to be delivered, and
120 in the signal mask associated with the handler to be invoked.
125 assigns a handler for a specific signal.
129 specifies a handler routine and mask
130 to be used when delivering the specified signal.
135 the system will deliver the signal to the process on a
141 is non-zero, the previous handling information for the signal
142 is returned to the user.
144 The following is a list of all signals
145 with names as in the include file
147 .Bl -column SIGVTALARMXX "create core imagexxx"
148 .It Sy "NAME Default Action Description"
149 .It Dv SIGHUP No " terminate process" " terminal line hangup"
150 .It Dv SIGINT No " terminate process" " interrupt program"
151 .It Dv SIGQUIT No " create core image" " quit program"
152 .It Dv SIGILL No " create core image" " illegal instruction"
153 .It Dv SIGTRAP No " create core image" " trace trap"
154 .It Dv SIGABRT No " create core image" Ta Xr abort 3
157 .It Dv SIGEMT No " create core image" " emulate instruction executed"
158 .It Dv SIGFPE No " create core image" " floating-point exception"
159 .It Dv SIGKILL No " terminate process" " kill program"
160 .It Dv SIGBUS No " create core image" " bus error"
161 .It Dv SIGSEGV No " create core image" " segmentation violation"
162 .It Dv SIGSYS No " create core image" " non-existent system call invoked"
163 .It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
164 .It Dv SIGALRM No " terminate process" " real-time timer expired"
165 .It Dv SIGTERM No " terminate process" " software termination signal"
166 .It Dv SIGURG No " discard signal" " urgent condition present on socket"
167 .It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
168 .It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
169 .It Dv SIGCONT No " discard signal" " continue after stop"
170 .It Dv SIGCHLD No " discard signal" " child status has changed"
171 .It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
172 .It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
173 .It Dv SIGIO No " discard signal" Tn " I/O"
174 is possible on a descriptor (see
176 .It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
178 .It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
180 .It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
182 .It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
184 .It Dv SIGWINCH No " discard signal" " Window size change"
185 .It Dv SIGINFO No " discard signal" " status request from keyboard"
186 .It Dv SIGUSR1 No " terminate process" " User defined signal 1"
187 .It Dv SIGUSR2 No " terminate process" " User defined signal 2"
190 Once a signal handler is installed, it remains installed
196 A signal-specific default action may be reset by
201 The defaults are process termination, possibly with core dump;
202 no action; stopping the process; or continuing the process.
203 See the above signal list for each signal's default action.
208 current and pending instances
209 of the signal are ignored and discarded.
211 If a signal is caught during the system calls listed below,
212 the call is normally restarted.
213 The call can be forced to terminate prematurely with an
215 error return by setting the
219 The affected system calls include
227 on a communications channel or a slow device (such as a terminal,
228 but not a regular file)
233 However, calls that have already committed are not restarted,
234 but instead return a partial success (for example, a short read count).
240 all signals, the signal mask, the signal stack,
241 and the restart/interrupt flags are inherited by the child.
245 system call reinstates the default
246 action for all signals which were caught and
247 resets all signals to be caught on the user stack.
248 Ignored signals remain ignored;
249 the signal mask remains the same;
250 signals that interrupt system calls continue to do so.
252 The mask specified in
254 is not allowed to block
258 This is done silently by the system.
262 flag is not available in
264 hence it should not be used if backward compatibility is needed.
270 The handler routine can be declared:
271 .Bd -literal -offset indent
272 void handler(sig, code, scp)
274 struct sigcontext *scp;
279 is the signal number, into which the hardware faults and traps are
280 mapped as defined below.
285 as given below or, for compatibility mode faults, the code provided by
286 the hardware (Compatibility mode faults are distinguished from the
297 structure (defined in
299 used to restore the context from before the signal.
304 will fail and no new signal handler will be installed if one
305 of the following occurs:
312 points to memory that is not a valid part of the process
318 is not a valid signal number.
320 An attempt is made to ignore or supply a handler for
342 This manual page is still confusing.