1.\" Copyright (c) 1980, 1990, 1993
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
7.\" 1. Redistributions of source code must retain the above copyright
8.\" notice, this list of conditions and the following disclaimer.
9.\" 2. Redistributions in binary form must reproduce the above copyright
10.\" notice, this list of conditions and the following disclaimer in the
11.\" documentation and/or other materials provided with the distribution.
12.\" 3. All advertising materials mentioning features or use of this software
13.\" must display the following acknowledgement:
14.\" This product includes software developed by the University of
15.\" California, Berkeley and its contributors.
16.\" 4. Neither the name of the University nor the names of its contributors
17.\" may be used to endorse or promote products derived from this software
18.\" without specific prior written permission.
19.\"
20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30.\" SUCH DAMAGE.
31.\"
32.\" From: @(#)sigaction.2 8.2 (Berkeley) 4/3/94
| 1.\" Copyright (c) 1980, 1990, 1993
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
7.\" 1. Redistributions of source code must retain the above copyright
8.\" notice, this list of conditions and the following disclaimer.
9.\" 2. Redistributions in binary form must reproduce the above copyright
10.\" notice, this list of conditions and the following disclaimer in the
11.\" documentation and/or other materials provided with the distribution.
12.\" 3. All advertising materials mentioning features or use of this software
13.\" must display the following acknowledgement:
14.\" This product includes software developed by the University of
15.\" California, Berkeley and its contributors.
16.\" 4. Neither the name of the University nor the names of its contributors
17.\" may be used to endorse or promote products derived from this software
18.\" without specific prior written permission.
19.\"
20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30.\" SUCH DAMAGE.
31.\"
32.\" From: @(#)sigaction.2 8.2 (Berkeley) 4/3/94
|
34.\"
35.Dd April 3, 1994
36.Dt SIGACTION 2
37.Os
38.Sh NAME
39.Nm sigaction
40.Nd software signal facilities
41.Sh SYNOPSIS
42.Fd #include <signal.h>
43.Bd -literal
44struct sigaction {
45 /*
46 * Signal handler function if flag SA_SIGINFO is not used and for
47 * SIG_DFL and SIG_IGN.
48 */
49 void (*sa_handler)(int);
50
51 /* Signal handler function if flag SA_SIGINFO is used */
52 void (*sa_sigaction)(int, siginfo_t *, void *);
53
54 sigset_t sa_mask; /* signal mask to apply */
55 int sa_flags; /* see signal options below */
56};
57.Ed
58.Ft int
59.Fn sigaction "int sig" "const struct sigaction *act" "struct sigaction *oact"
60.Sh DESCRIPTION
61The system defines a set of signals that may be delivered to a process.
62Signal delivery resembles the occurrence of a hardware interrupt:
63the signal is normally blocked from further occurrence, the current process
64context is saved, and a new one is built. A process may specify a
65.Em handler
66to which a signal is delivered, or specify that a signal is to be
67.Em ignored .
68A process may also specify that a default action is to be taken
69by the system when a signal occurs.
70A signal may also be
71.Em blocked ,
72in which case its delivery is postponed until it is
73.Em unblocked .
74The action to be taken on delivery is determined at the time
75of delivery.
76Normally, signal handlers execute on the current stack
77of the process. This may be changed, on a per-handler basis,
78so that signals are taken on a special
79.Em "signal stack" .
80.Pp
81Signal routines normally execute with the signal that caused their
82invocation
83.Em blocked ,
84but other signals may yet occur.
85A global
86.Em "signal mask"
87defines the set of signals currently blocked from delivery
88to a process. The signal mask for a process is initialized
89from that of its parent (normally empty). It
90may be changed with a
91.Xr sigprocmask 2
92call, or when a signal is delivered to the process.
93.Pp
94When a signal
95condition arises for a process, the signal is added to a set of
96signals pending for the process.
97If the signal is not currently
98.Em blocked
99by the process then it is delivered to the process.
100Signals may be delivered any time a process enters the operating system
101(e.g., during a system call, page fault or trap, or clock interrupt).
102If multiple signals are ready to be delivered at the same time,
103any signals that could be caused by traps are delivered first.
104Additional signals may be processed at the same time, with each
105appearing to interrupt the handlers for the previous signals
106before their first instructions.
107The set of pending signals is returned by the
108.Xr sigpending 2
109function.
110When a caught signal
111is delivered, the current state of the process is saved,
112a new signal mask is calculated (as described below),
113and the signal handler is invoked. The call to the handler
114is arranged so that if the signal handling routine returns
115normally the process will resume execution in the context
116from before the signal's delivery.
117If the process wishes to resume in a different context, then it
118must arrange to restore the previous context itself.
119.Pp
120When a signal is delivered to a process a new signal mask is
121installed for the duration of the process' signal handler
122(or until a
123.Xr sigprocmask
124call is made).
125This mask is formed by taking the union of the current signal mask set,
126the signal to be delivered, and
127the signal mask associated with the handler to be invoked.
128.Pp
129.Fn Sigaction
130assigns an action for a signal specified by
131.Fa sig .
132If
133.Fa act
134is non-zero, it
135specifies an action
136.Pf ( Dv SIG_DFL ,
137.Dv SIG_IGN ,
138or a handler routine) and mask
139to be used when delivering the specified signal.
140If
141.Fa oact
142is non-zero, the previous handling information for the signal
143is returned to the user.
144.Pp
145Once a signal handler is installed, it normally remains installed
146until another
147.Fn sigaction
148call is made, or an
149.Xr execve 2
150is performed.
151A signal-specific default action may be reset by
152setting
153.Fa sa_handler
154to
155.Dv SIG_DFL .
156The defaults are process termination, possibly with core dump;
157no action; stopping the process; or continuing the process.
158See the signal list below for each signal's default action.
159If
160.Fa sa_handler
161is
162.Dv SIG_DFL ,
163the default action for the signal is to discard the signal,
164and if a signal is pending,
165the pending signal is discarded even if the signal is masked.
166If
167.Fa sa_handler
168is set to
169.Dv SIG_IGN
170current and pending instances
171of the signal are ignored and discarded.
172.Pp
173Options may be specified by setting
174.Em sa_flags .
175The meaning of the various bits is as follows:
176.Bl -tag -offset indent -width SA_RESETHANDXX
177.It Dv SA_NOCLDSTOP
178If this bit is set when installing a catching function
179for the
180.Dv SIGCHLD
181signal,
182the
183.Dv SIGCHLD
184signal will be generated only when a child process exits,
185not when a child process stops.
186.It Dv SA_NOCLDWAIT
187If this bit is set when calling
188.Fn sigaction
189for the
190.Dv SIGCHLD
191signal, the system will not create zombie processes when children of
192the calling process exit. If the calling process subsequently issues
193a
194.Xr wait 2
195(or equivalent), it blocks until all of the calling process's child
196processes terminate, and then returns a value of -1 with errno set to
197.Dv ECHILD .
198.It Dv SA_ONSTACK
199If this bit is set, the system will deliver the signal to the process
200on a
201.Em "signal stack" ,
202specified with
203.Xr sigaltstack 2 .
204.It Dv SA_NODEFER
205If this bit is set, further occurrences of the delivered signal are
206not masked during the execution of the handler.
207.It Dv SA_RESETHAND
208If this bit is set, the handler is reset back to
209.Dv SIG_DFL
210at the moment the signal is delivered.
211.It Dv SA_SIGINFO
212If this bit is set, the handler function is assumed to be pointed to
213by the sa_sigaction member of struct sigaction and should match the
214prototype shown above or as below in
215.Sx EXAMPLES .
216This bit should not be set when assigning
217.Dv SIG_DFL
218or
219.Dv SIG_IGN .
220.El
221.Pp
222If a signal is caught during the system calls listed below,
223the call may be forced to terminate
224with the error
225.Dv EINTR ,
226the call may return with a data transfer shorter than requested,
227or the call may be restarted.
228Restart of pending calls is requested
229by setting the
230.Dv SA_RESTART
231bit in
232.Ar sa_flags .
233The affected system calls include
234.Xr open 2 ,
235.Xr read 2 ,
236.Xr write 2 ,
237.Xr sendto 2 ,
238.Xr recvfrom 2 ,
239.Xr sendmsg 2
240and
241.Xr recvmsg 2
242on a communications channel or a slow device (such as a terminal,
243but not a regular file)
244and during a
245.Xr wait 2
246or
247.Xr ioctl 2 .
248However, calls that have already committed are not restarted,
249but instead return a partial success (for example, a short read count).
250.Pp
251After a
252.Xr fork 2
253or
254.Xr vfork 2
255all signals, the signal mask, the signal stack,
256and the restart/interrupt flags are inherited by the child.
257.Pp
258.Xr Execve 2
259reinstates the default
260action for all signals which were caught and
261resets all signals to be caught on the user stack.
262Ignored signals remain ignored;
263the signal mask remains the same;
264signals that restart pending system calls continue to do so.
265.Pp
266The following is a list of all signals
267with names as in the include file
268.Aq Pa signal.h :
269.Bl -column SIGVTALARMXX "create core imagexxx"
270.It Sy " NAME " " Default Action " " Description"
271.It Dv SIGHUP No " terminate process" " terminal line hangup"
272.It Dv SIGINT No " terminate process" " interrupt program"
273.It Dv SIGQUIT No " create core image" " quit program"
274.It Dv SIGILL No " create core image" " illegal instruction"
275.It Dv SIGTRAP No " create core image" " trace trap"
276.It Dv SIGABRT No " create core image" Xr abort 3
277call (formerly
278.Dv SIGIOT )
279.It Dv SIGEMT No " create core image" " emulate instruction executed"
280.It Dv SIGFPE No " create core image" " floating-point exception"
281.It Dv SIGKILL No " terminate process" " kill program"
282.It Dv SIGBUS No " create core image" " bus error"
283.It Dv SIGSEGV No " create core image" " segmentation violation"
284.It Dv SIGSYS No " create core image" " non-existent system call invoked"
285.It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
286.It Dv SIGALRM No " terminate process" " real-time timer expired"
287.It Dv SIGTERM No " terminate process" " software termination signal"
288.It Dv SIGURG No " discard signal" " urgent condition present on socket"
289.It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
290.It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
291.It Dv SIGCONT No " discard signal" " continue after stop"
292.It Dv SIGCHLD No " discard signal" " child status has changed"
293.It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
294.It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
295.It Dv SIGIO No " discard signal" Tn " I/O"
296is possible on a descriptor (see
297.Xr fcntl 2 )
298.It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
299.Xr setrlimit 2 )
300.It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
301.Xr setrlimit 2 )
302.It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
303.Xr setitimer 2 )
304.It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
305.Xr setitimer 2 )
306.It Dv SIGWINCH No " discard signal" " Window size change"
307.It Dv SIGINFO No " discard signal" " status request from keyboard"
308.It Dv SIGUSR1 No " terminate process" " User defined signal 1"
309.It Dv SIGUSR2 No " terminate process" " User defined signal 2"
310.El
311.Sh NOTE
312The
313.Fa sa_mask
314field specified in
315.Fa act
316is not allowed to block
317.Dv SIGKILL
318or
319.Dv SIGSTOP .
320Any attempt to do so will be silently ignored.
321.Pp
322The following functions are either reentrant or not interruptible
| 34.\"
35.Dd April 3, 1994
36.Dt SIGACTION 2
37.Os
38.Sh NAME
39.Nm sigaction
40.Nd software signal facilities
41.Sh SYNOPSIS
42.Fd #include <signal.h>
43.Bd -literal
44struct sigaction {
45 /*
46 * Signal handler function if flag SA_SIGINFO is not used and for
47 * SIG_DFL and SIG_IGN.
48 */
49 void (*sa_handler)(int);
50
51 /* Signal handler function if flag SA_SIGINFO is used */
52 void (*sa_sigaction)(int, siginfo_t *, void *);
53
54 sigset_t sa_mask; /* signal mask to apply */
55 int sa_flags; /* see signal options below */
56};
57.Ed
58.Ft int
59.Fn sigaction "int sig" "const struct sigaction *act" "struct sigaction *oact"
60.Sh DESCRIPTION
61The system defines a set of signals that may be delivered to a process.
62Signal delivery resembles the occurrence of a hardware interrupt:
63the signal is normally blocked from further occurrence, the current process
64context is saved, and a new one is built. A process may specify a
65.Em handler
66to which a signal is delivered, or specify that a signal is to be
67.Em ignored .
68A process may also specify that a default action is to be taken
69by the system when a signal occurs.
70A signal may also be
71.Em blocked ,
72in which case its delivery is postponed until it is
73.Em unblocked .
74The action to be taken on delivery is determined at the time
75of delivery.
76Normally, signal handlers execute on the current stack
77of the process. This may be changed, on a per-handler basis,
78so that signals are taken on a special
79.Em "signal stack" .
80.Pp
81Signal routines normally execute with the signal that caused their
82invocation
83.Em blocked ,
84but other signals may yet occur.
85A global
86.Em "signal mask"
87defines the set of signals currently blocked from delivery
88to a process. The signal mask for a process is initialized
89from that of its parent (normally empty). It
90may be changed with a
91.Xr sigprocmask 2
92call, or when a signal is delivered to the process.
93.Pp
94When a signal
95condition arises for a process, the signal is added to a set of
96signals pending for the process.
97If the signal is not currently
98.Em blocked
99by the process then it is delivered to the process.
100Signals may be delivered any time a process enters the operating system
101(e.g., during a system call, page fault or trap, or clock interrupt).
102If multiple signals are ready to be delivered at the same time,
103any signals that could be caused by traps are delivered first.
104Additional signals may be processed at the same time, with each
105appearing to interrupt the handlers for the previous signals
106before their first instructions.
107The set of pending signals is returned by the
108.Xr sigpending 2
109function.
110When a caught signal
111is delivered, the current state of the process is saved,
112a new signal mask is calculated (as described below),
113and the signal handler is invoked. The call to the handler
114is arranged so that if the signal handling routine returns
115normally the process will resume execution in the context
116from before the signal's delivery.
117If the process wishes to resume in a different context, then it
118must arrange to restore the previous context itself.
119.Pp
120When a signal is delivered to a process a new signal mask is
121installed for the duration of the process' signal handler
122(or until a
123.Xr sigprocmask
124call is made).
125This mask is formed by taking the union of the current signal mask set,
126the signal to be delivered, and
127the signal mask associated with the handler to be invoked.
128.Pp
129.Fn Sigaction
130assigns an action for a signal specified by
131.Fa sig .
132If
133.Fa act
134is non-zero, it
135specifies an action
136.Pf ( Dv SIG_DFL ,
137.Dv SIG_IGN ,
138or a handler routine) and mask
139to be used when delivering the specified signal.
140If
141.Fa oact
142is non-zero, the previous handling information for the signal
143is returned to the user.
144.Pp
145Once a signal handler is installed, it normally remains installed
146until another
147.Fn sigaction
148call is made, or an
149.Xr execve 2
150is performed.
151A signal-specific default action may be reset by
152setting
153.Fa sa_handler
154to
155.Dv SIG_DFL .
156The defaults are process termination, possibly with core dump;
157no action; stopping the process; or continuing the process.
158See the signal list below for each signal's default action.
159If
160.Fa sa_handler
161is
162.Dv SIG_DFL ,
163the default action for the signal is to discard the signal,
164and if a signal is pending,
165the pending signal is discarded even if the signal is masked.
166If
167.Fa sa_handler
168is set to
169.Dv SIG_IGN
170current and pending instances
171of the signal are ignored and discarded.
172.Pp
173Options may be specified by setting
174.Em sa_flags .
175The meaning of the various bits is as follows:
176.Bl -tag -offset indent -width SA_RESETHANDXX
177.It Dv SA_NOCLDSTOP
178If this bit is set when installing a catching function
179for the
180.Dv SIGCHLD
181signal,
182the
183.Dv SIGCHLD
184signal will be generated only when a child process exits,
185not when a child process stops.
186.It Dv SA_NOCLDWAIT
187If this bit is set when calling
188.Fn sigaction
189for the
190.Dv SIGCHLD
191signal, the system will not create zombie processes when children of
192the calling process exit. If the calling process subsequently issues
193a
194.Xr wait 2
195(or equivalent), it blocks until all of the calling process's child
196processes terminate, and then returns a value of -1 with errno set to
197.Dv ECHILD .
198.It Dv SA_ONSTACK
199If this bit is set, the system will deliver the signal to the process
200on a
201.Em "signal stack" ,
202specified with
203.Xr sigaltstack 2 .
204.It Dv SA_NODEFER
205If this bit is set, further occurrences of the delivered signal are
206not masked during the execution of the handler.
207.It Dv SA_RESETHAND
208If this bit is set, the handler is reset back to
209.Dv SIG_DFL
210at the moment the signal is delivered.
211.It Dv SA_SIGINFO
212If this bit is set, the handler function is assumed to be pointed to
213by the sa_sigaction member of struct sigaction and should match the
214prototype shown above or as below in
215.Sx EXAMPLES .
216This bit should not be set when assigning
217.Dv SIG_DFL
218or
219.Dv SIG_IGN .
220.El
221.Pp
222If a signal is caught during the system calls listed below,
223the call may be forced to terminate
224with the error
225.Dv EINTR ,
226the call may return with a data transfer shorter than requested,
227or the call may be restarted.
228Restart of pending calls is requested
229by setting the
230.Dv SA_RESTART
231bit in
232.Ar sa_flags .
233The affected system calls include
234.Xr open 2 ,
235.Xr read 2 ,
236.Xr write 2 ,
237.Xr sendto 2 ,
238.Xr recvfrom 2 ,
239.Xr sendmsg 2
240and
241.Xr recvmsg 2
242on a communications channel or a slow device (such as a terminal,
243but not a regular file)
244and during a
245.Xr wait 2
246or
247.Xr ioctl 2 .
248However, calls that have already committed are not restarted,
249but instead return a partial success (for example, a short read count).
250.Pp
251After a
252.Xr fork 2
253or
254.Xr vfork 2
255all signals, the signal mask, the signal stack,
256and the restart/interrupt flags are inherited by the child.
257.Pp
258.Xr Execve 2
259reinstates the default
260action for all signals which were caught and
261resets all signals to be caught on the user stack.
262Ignored signals remain ignored;
263the signal mask remains the same;
264signals that restart pending system calls continue to do so.
265.Pp
266The following is a list of all signals
267with names as in the include file
268.Aq Pa signal.h :
269.Bl -column SIGVTALARMXX "create core imagexxx"
270.It Sy " NAME " " Default Action " " Description"
271.It Dv SIGHUP No " terminate process" " terminal line hangup"
272.It Dv SIGINT No " terminate process" " interrupt program"
273.It Dv SIGQUIT No " create core image" " quit program"
274.It Dv SIGILL No " create core image" " illegal instruction"
275.It Dv SIGTRAP No " create core image" " trace trap"
276.It Dv SIGABRT No " create core image" Xr abort 3
277call (formerly
278.Dv SIGIOT )
279.It Dv SIGEMT No " create core image" " emulate instruction executed"
280.It Dv SIGFPE No " create core image" " floating-point exception"
281.It Dv SIGKILL No " terminate process" " kill program"
282.It Dv SIGBUS No " create core image" " bus error"
283.It Dv SIGSEGV No " create core image" " segmentation violation"
284.It Dv SIGSYS No " create core image" " non-existent system call invoked"
285.It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
286.It Dv SIGALRM No " terminate process" " real-time timer expired"
287.It Dv SIGTERM No " terminate process" " software termination signal"
288.It Dv SIGURG No " discard signal" " urgent condition present on socket"
289.It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
290.It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
291.It Dv SIGCONT No " discard signal" " continue after stop"
292.It Dv SIGCHLD No " discard signal" " child status has changed"
293.It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
294.It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
295.It Dv SIGIO No " discard signal" Tn " I/O"
296is possible on a descriptor (see
297.Xr fcntl 2 )
298.It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
299.Xr setrlimit 2 )
300.It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
301.Xr setrlimit 2 )
302.It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
303.Xr setitimer 2 )
304.It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
305.Xr setitimer 2 )
306.It Dv SIGWINCH No " discard signal" " Window size change"
307.It Dv SIGINFO No " discard signal" " status request from keyboard"
308.It Dv SIGUSR1 No " terminate process" " User defined signal 1"
309.It Dv SIGUSR2 No " terminate process" " User defined signal 2"
310.El
311.Sh NOTE
312The
313.Fa sa_mask
314field specified in
315.Fa act
316is not allowed to block
317.Dv SIGKILL
318or
319.Dv SIGSTOP .
320Any attempt to do so will be silently ignored.
321.Pp
322The following functions are either reentrant or not interruptible
|
324invoke them, without restriction, from signal-catching functions:
325.Pp
326Base Interfaces:
327.Pp
328.Fn _exit ,
329.Fn access ,
330.Fn alarm ,
331.Fn cfgetispeed ,
332.Fn cfgetospeed ,
333.Fn cfsetispeed ,
334.Fn cfsetospeed ,
335.Fn chdir ,
336.Fn chmod ,
337.Fn chown ,
338.Fn close ,
339.Fn creat ,
340.Fn dup ,
341.Fn dup2 ,
342.Fn execle ,
343.Fn execve ,
344.Fn fcntl ,
345.Fn fork ,
346.Fn fpathconf ,
347.Fn fstat ,
348.Fn fsync ,
349.Fn getegid ,
350.Fn geteuid ,
351.Fn getgid ,
352.Fn getgroups ,
353.Fn getpgrp ,
354.Fn getpid ,
355.Fn getppid ,
356.Fn getuid ,
357.Fn kill ,
358.Fn link ,
359.Fn lseek ,
360.Fn mkdir ,
361.Fn mkfifo ,
362.Fn open ,
363.Fn pathconf ,
364.Fn pause ,
365.Fn pipe ,
366.Fn raise ,
367.Fn read ,
368.Fn rename ,
369.Fn rmdir ,
370.Fn setgid ,
371.Fn setpgid ,
372.Fn setsid ,
373.Fn setuid ,
374.Fn sigaction ,
375.Fn sigaddset ,
376.Fn sigdelset ,
377.Fn sigemptyset ,
378.Fn sigfillset ,
379.Fn sigismember ,
380.Fn signal ,
381.Fn sigpending ,
382.Fn sigprocmask ,
383.Fn sigsuspend ,
384.Fn sleep ,
385.Fn stat ,
386.Fn sysconf ,
387.Fn tcdrain ,
388.Fn tcflow ,
389.Fn tcflush ,
390.Fn tcgetattr ,
391.Fn tcgetpgrp ,
392.Fn tcsendbreak ,
393.Fn tcsetattr ,
394.Fn tcsetpgrp ,
395.Fn time ,
396.Fn times ,
397.Fn umask ,
398.Fn uname ,
399.Fn unlink ,
400.Fn utime ,
401.Fn wait ,
402.Fn waitpid ,
403.Fn write .
404.Pp
405Realtime Interfaces:
406.Pp
407.Fn aio_error ,
408.Fn clock_gettime ,
409.Fn sigpause ,
410.Fn timer_getoverrun ,
411.Fn aio_return ,
412.Fn fdatasync ,
413.Fn sigqueue ,
414.Fn timer_gettime ,
415.Fn aio_suspend ,
416.Fn sem_post ,
417.Fn sigset ,
418.Fn timer_settime .
419.Pp
420All functions not in the above lists are considered to be unsafe
421with respect to signals. That is to say, the behaviour of such
422functions when called from a signal handler is undefined.
423.Sh RETURN VALUES
424A 0 value indicated that the call succeeded. A \-1 return value
425indicates an error occurred and
426.Va errno
427is set to indicated the reason.
428.Sh EXAMPLES
429There are three possible prototypes the handler may match:
430.Bl -tag -offset indent -width short
431.It ANSI C:
432.Fd
433void handler(int);
434.It Traditional BSD style:
435.Fd
436void handler(int, int code, struct sigcontext *scp);
437.It POSIX SA_SIGINFO:
438.Fd
439void handler(int, siginfo_t *info, void *context);
440.El
441.Pp
442The handler function should match the SA_SIGINFO prototype if the
443SA_SIGINFO bit is set in flags.
444It then should be pointed to by the
445.Dv sa_siginfo
446member of
447.Dv struct sigaction .
448Note that you should not assign SIG_DFL or SIG_IGN this way.
449.Pp
450If the SA_SIGINFO flag is not set, the handler function should match
451either the ANSI C or traditional BSD prototype and be pointed to by
452the
453.Dv sa_handler
454member of
455.Dv struct sigaction .
456In pratice,
457.Fx
458always sends the three arguments of the latter and since the ANSI C
459prototype is a subset, both will work.
460The
461.Dv sa_handler
462member declaration in
463.Fx
464include files is that of ANSI C (as required by POSIX),
465so a function pointer of a BSD-style function needs to be casted to
466compile without warning.
467The traditional BSD style is not portable and since its capabilities
468are a full subset of a SA_SIGINFO handler,
469its use is deprecated.
470.Pp
471The
472.Fa sig
473argument is the signal number, one of the
474.Dv SIG...
475values from <signal.h>.
476.Pp
477The
478.Fa code
479argument of the BSD-style handler and the
480.Dv si_code
481member of the
482.Dv info
483argument to a SA_SIGINFO handler contain a numeric code explaning the
484cause of the signal, usually one of the
485.Dv SI_...
486values from
487<sys/signal.h> or codes specific to a signal, i.e. one of the
488.Dv FPE_...
489values for SIGFPE.
490.Pp
491The
492.Fa scp
493argument to a BSD-style handler points to an instance of struct
494sigcontext.
495.Pp
496The
497.Fa context
498argument to a POSIX SA_SIGINFO handler points to an instance of
499mcontext_t.
500.Sh ERRORS
501.Fn Sigaction
502will fail and no new signal handler will be installed if one
503of the following occurs:
504.Bl -tag -width Er
505.It Bq Er EFAULT
506Either
507.Fa act
508or
509.Fa oact
510points to memory that is not a valid part of the process
511address space.
512.It Bq Er EINVAL
513.Fa Sig
514is not a valid signal number.
515.It Bq Er EINVAL
516An attempt is made to ignore or supply a handler for
517.Dv SIGKILL
518or
519.Dv SIGSTOP .
520.El
521.Sh STANDARDS
522The
523.Fn sigaction
524function call is expected to conform to
525.St -p1003.1-90 .
526The
527.Dv SA_ONSTACK
528and
529.Dv SA_RESTART
530flags are Berkeley extensions,
531as are the signals,
532.Dv SIGTRAP ,
533.Dv SIGEMT ,
534.Dv SIGBUS ,
535.Dv SIGSYS ,
536.Dv SIGURG ,
537.Dv SIGIO ,
538.Dv SIGXCPU ,
539.Dv SIGXFSZ ,
540.Dv SIGVTALRM ,
541.Dv SIGPROF ,
542.Dv SIGWINCH ,
543and
544.Dv SIGINFO .
545Those signals are available on most
546.Tn BSD Ns \-derived
547systems.
548The
549.Dv SA_NODEFER
550and
551.Dv SA_RESETHAND
552flags are intended for backwards compatibility with other operating
553systems. The
554.Dv SA_NOCLDSTOP ,
555and
556.Dv SA_NOCLDWAIT
557.\" and
558.\" SA_SIGINFO
559flags are featuring options commonly found in other operating systems.
560.Sh SEE ALSO
561.Xr kill 1 ,
562.Xr kill 2 ,
563.Xr ptrace 2 ,
564.Xr sigaltstack 2 ,
565.Xr sigblock 2 ,
566.Xr sigpause 2 ,
567.Xr sigpending 2 ,
568.Xr sigprocmask 2 ,
569.Xr sigsetmask 2 ,
570.Xr sigsuspend 2 ,
571.Xr sigvec 2 ,
572.Xr wait 2 ,
573.Xr fpsetmask 3 ,
574.Xr setjmp 3 ,
575.Xr siginterrupt 3 ,
576.Xr sigsetops 3 ,
577.Xr tty 4
| 325invoke them, without restriction, from signal-catching functions:
326.Pp
327Base Interfaces:
328.Pp
329.Fn _exit ,
330.Fn access ,
331.Fn alarm ,
332.Fn cfgetispeed ,
333.Fn cfgetospeed ,
334.Fn cfsetispeed ,
335.Fn cfsetospeed ,
336.Fn chdir ,
337.Fn chmod ,
338.Fn chown ,
339.Fn close ,
340.Fn creat ,
341.Fn dup ,
342.Fn dup2 ,
343.Fn execle ,
344.Fn execve ,
345.Fn fcntl ,
346.Fn fork ,
347.Fn fpathconf ,
348.Fn fstat ,
349.Fn fsync ,
350.Fn getegid ,
351.Fn geteuid ,
352.Fn getgid ,
353.Fn getgroups ,
354.Fn getpgrp ,
355.Fn getpid ,
356.Fn getppid ,
357.Fn getuid ,
358.Fn kill ,
359.Fn link ,
360.Fn lseek ,
361.Fn mkdir ,
362.Fn mkfifo ,
363.Fn open ,
364.Fn pathconf ,
365.Fn pause ,
366.Fn pipe ,
367.Fn raise ,
368.Fn read ,
369.Fn rename ,
370.Fn rmdir ,
371.Fn setgid ,
372.Fn setpgid ,
373.Fn setsid ,
374.Fn setuid ,
375.Fn sigaction ,
376.Fn sigaddset ,
377.Fn sigdelset ,
378.Fn sigemptyset ,
379.Fn sigfillset ,
380.Fn sigismember ,
381.Fn signal ,
382.Fn sigpending ,
383.Fn sigprocmask ,
384.Fn sigsuspend ,
385.Fn sleep ,
386.Fn stat ,
387.Fn sysconf ,
388.Fn tcdrain ,
389.Fn tcflow ,
390.Fn tcflush ,
391.Fn tcgetattr ,
392.Fn tcgetpgrp ,
393.Fn tcsendbreak ,
394.Fn tcsetattr ,
395.Fn tcsetpgrp ,
396.Fn time ,
397.Fn times ,
398.Fn umask ,
399.Fn uname ,
400.Fn unlink ,
401.Fn utime ,
402.Fn wait ,
403.Fn waitpid ,
404.Fn write .
405.Pp
406Realtime Interfaces:
407.Pp
408.Fn aio_error ,
409.Fn clock_gettime ,
410.Fn sigpause ,
411.Fn timer_getoverrun ,
412.Fn aio_return ,
413.Fn fdatasync ,
414.Fn sigqueue ,
415.Fn timer_gettime ,
416.Fn aio_suspend ,
417.Fn sem_post ,
418.Fn sigset ,
419.Fn timer_settime .
420.Pp
421All functions not in the above lists are considered to be unsafe
422with respect to signals. That is to say, the behaviour of such
423functions when called from a signal handler is undefined.
424.Sh RETURN VALUES
425A 0 value indicated that the call succeeded. A \-1 return value
426indicates an error occurred and
427.Va errno
428is set to indicated the reason.
429.Sh EXAMPLES
430There are three possible prototypes the handler may match:
431.Bl -tag -offset indent -width short
432.It ANSI C:
433.Fd
434void handler(int);
435.It Traditional BSD style:
436.Fd
437void handler(int, int code, struct sigcontext *scp);
438.It POSIX SA_SIGINFO:
439.Fd
440void handler(int, siginfo_t *info, void *context);
441.El
442.Pp
443The handler function should match the SA_SIGINFO prototype if the
444SA_SIGINFO bit is set in flags.
445It then should be pointed to by the
446.Dv sa_siginfo
447member of
448.Dv struct sigaction .
449Note that you should not assign SIG_DFL or SIG_IGN this way.
450.Pp
451If the SA_SIGINFO flag is not set, the handler function should match
452either the ANSI C or traditional BSD prototype and be pointed to by
453the
454.Dv sa_handler
455member of
456.Dv struct sigaction .
457In pratice,
458.Fx
459always sends the three arguments of the latter and since the ANSI C
460prototype is a subset, both will work.
461The
462.Dv sa_handler
463member declaration in
464.Fx
465include files is that of ANSI C (as required by POSIX),
466so a function pointer of a BSD-style function needs to be casted to
467compile without warning.
468The traditional BSD style is not portable and since its capabilities
469are a full subset of a SA_SIGINFO handler,
470its use is deprecated.
471.Pp
472The
473.Fa sig
474argument is the signal number, one of the
475.Dv SIG...
476values from <signal.h>.
477.Pp
478The
479.Fa code
480argument of the BSD-style handler and the
481.Dv si_code
482member of the
483.Dv info
484argument to a SA_SIGINFO handler contain a numeric code explaning the
485cause of the signal, usually one of the
486.Dv SI_...
487values from
488<sys/signal.h> or codes specific to a signal, i.e. one of the
489.Dv FPE_...
490values for SIGFPE.
491.Pp
492The
493.Fa scp
494argument to a BSD-style handler points to an instance of struct
495sigcontext.
496.Pp
497The
498.Fa context
499argument to a POSIX SA_SIGINFO handler points to an instance of
500mcontext_t.
501.Sh ERRORS
502.Fn Sigaction
503will fail and no new signal handler will be installed if one
504of the following occurs:
505.Bl -tag -width Er
506.It Bq Er EFAULT
507Either
508.Fa act
509or
510.Fa oact
511points to memory that is not a valid part of the process
512address space.
513.It Bq Er EINVAL
514.Fa Sig
515is not a valid signal number.
516.It Bq Er EINVAL
517An attempt is made to ignore or supply a handler for
518.Dv SIGKILL
519or
520.Dv SIGSTOP .
521.El
522.Sh STANDARDS
523The
524.Fn sigaction
525function call is expected to conform to
526.St -p1003.1-90 .
527The
528.Dv SA_ONSTACK
529and
530.Dv SA_RESTART
531flags are Berkeley extensions,
532as are the signals,
533.Dv SIGTRAP ,
534.Dv SIGEMT ,
535.Dv SIGBUS ,
536.Dv SIGSYS ,
537.Dv SIGURG ,
538.Dv SIGIO ,
539.Dv SIGXCPU ,
540.Dv SIGXFSZ ,
541.Dv SIGVTALRM ,
542.Dv SIGPROF ,
543.Dv SIGWINCH ,
544and
545.Dv SIGINFO .
546Those signals are available on most
547.Tn BSD Ns \-derived
548systems.
549The
550.Dv SA_NODEFER
551and
552.Dv SA_RESETHAND
553flags are intended for backwards compatibility with other operating
554systems. The
555.Dv SA_NOCLDSTOP ,
556and
557.Dv SA_NOCLDWAIT
558.\" and
559.\" SA_SIGINFO
560flags are featuring options commonly found in other operating systems.
561.Sh SEE ALSO
562.Xr kill 1 ,
563.Xr kill 2 ,
564.Xr ptrace 2 ,
565.Xr sigaltstack 2 ,
566.Xr sigblock 2 ,
567.Xr sigpause 2 ,
568.Xr sigpending 2 ,
569.Xr sigprocmask 2 ,
570.Xr sigsetmask 2 ,
571.Xr sigsuspend 2 ,
572.Xr sigvec 2 ,
573.Xr wait 2 ,
574.Xr fpsetmask 3 ,
575.Xr setjmp 3 ,
576.Xr siginterrupt 3 ,
577.Xr sigsetops 3 ,
578.Xr tty 4
|