[apple/libc.git] / gen / signal.3

.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)signal.3	8.3 (Berkeley) 4/19/94
.\" $FreeBSD: src/lib/libc/gen/signal.3,v 1.28 2001/10/01 16:08:51 ru Exp $
.\"
.Dd April 19, 1994
.Dt SIGNAL 3
.Os
.Sh NAME
.Nm signal
.Nd simplified software signal facilities
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.\" The following is Quite Ugly, but syntactically correct.  Don't try to
.\" fix it.
.Ft void \*(lp*
.Fn signal "int sig" "void \*(lp*func\*(rp\*(lpint\*(rp\*(rp\*(rp\*(lpint"
.Pp
or in
.Fx Ns 's
equivalent but easier to read typedef'd version:
.Ft typedef "void \*(lp*sig_t\*(rp \*(lpint\*(rp"
.Ft sig_t
.Fn signal "int sig" "sig_t func"
.Sh DESCRIPTION
This
.Fn signal
facility
is a simplified interface to the more general
.Xr sigaction 2
facility.
.Pp
Signals allow the manipulation of a process from outside its
domain as well as allowing the process to manipulate itself or
copies of itself (children). There are two general types of signals:
those that cause termination of a process and those that do not.
Signals which cause termination of a program might result from
an irrecoverable error or might be the result of a user at a terminal
typing the `interrupt' character.
Signals are used when a process is stopped because it wishes to access
its control terminal while in the background (see
.Xr tty 4 ) .
Signals are optionally generated
when a process resumes after being stopped,
when the status of child processes changes,
or when input is ready at the control terminal.
Most signals result in the termination of the process receiving them
if no action
is taken; some signals instead cause the process receiving them
to be stopped, or are simply discarded if the process has not
requested otherwise.
Except for the
.Dv SIGKILL
and
.Dv SIGSTOP
signals, the
.Fn signal
function allows for a signal to be caught, to be ignored, or to generate
an interrupt.
These signals are defined in the file
.Aq Pa signal.h :
.Bl -column SIGVTALARMXX "create core imagexxx"
.It Sy "Name	Default Action	Description"
.It Dv SIGHUP Ta "terminate process" Ta "terminal line hangup"
.It Dv SIGINT Ta "terminate process" Ta "interrupt program"
.It Dv SIGQUIT Ta "create core image" Ta "quit program"
.It Dv SIGILL Ta "create core image" Ta "illegal instruction"
.It Dv SIGTRAP Ta "create core image" Ta "trace trap"
.It Dv SIGABRT Ta "create core image" Ta "abort program"
(formerly
.Dv SIGIOT )
.It Dv SIGEMT Ta "create core image" Ta "emulate instruction executed"
.It Dv SIGFPE Ta "create core image" Ta "floating-point exception"
.It Dv SIGKILL Ta "terminate process" Ta "kill program"
.It Dv SIGBUS Ta "create core image" Ta "bus error"
.It Dv SIGSEGV Ta "create core image" Ta "segmentation violation"
.It Dv SIGSYS Ta "create core image" Ta "non-existent system call invoked"
.It Dv SIGPIPE Ta "terminate process" Ta "write on a pipe with no reader"
.It Dv SIGALRM Ta "terminate process" Ta "real-time timer expired"
.It Dv SIGTERM Ta "terminate process" Ta "software termination signal"
.It Dv SIGURG Ta "discard signal" Ta "urgent condition present on socket"
.It Dv SIGSTOP Ta "stop process" Ta "stop (cannot be caught or ignored)"
.It Dv SIGTSTP Ta "stop process" Ta "stop signal generated from keyboard"
.It Dv SIGCONT Ta "discard signal" Ta "continue after stop"
.It Dv SIGCHLD Ta "discard signal" Ta "child status has changed"
.It Dv SIGTTIN Ta "stop process" Ta "background read attempted from control terminal"
.It Dv SIGTTOU Ta "stop process" Ta "background write attempted to control terminal"
.It Dv SIGIO Ta "discard signal" Ta Tn "I/O"
is possible on a descriptor (see
.Xr fcntl 2 )
.It Dv SIGXCPU Ta "terminate process" Ta "cpu time limit exceeded (see"
.Xr setrlimit 2 )
.It Dv SIGXFSZ Ta "terminate process" Ta "file size limit exceeded (see"
.Xr setrlimit 2 )
.It Dv SIGVTALRM Ta "terminate process" Ta "virtual time alarm (see"
.Xr setitimer 2 )
.It Dv SIGPROF Ta "terminate process" Ta "profiling timer alarm (see"
.Xr setitimer 2 )
.It Dv SIGWINCH Ta "discard signal" Ta "Window size change"
.It Dv SIGINFO Ta "discard signal" Ta "status request from keyboard"
.It Dv SIGUSR1 Ta "terminate process" Ta "User defined signal 1"
.It Dv SIGUSR2 Ta "terminate process" Ta "User defined signal 2"
.El
.Pp
The
.Fa sig
parameter specifies which signal was received.
The
.Fa func
procedure allows a user to choose the action upon receipt of a signal.
To set the default action of the signal to occur as listed above,
.Fa func
should be
.Dv SIG_DFL .
A
.Dv SIG_DFL
resets the default action.
To ignore the signal
.Fa func
should be
.Dv SIG_IGN .
This will cause subsequent instances of the signal to be ignored
and pending instances to be discarded.
If
.Dv SIG_IGN
is not used,
further occurrences of the signal are
automatically blocked and
.Fa func
is called.
.Pp
The handled signal is unblocked when the
function returns and
the process continues from where it left off when the signal occurred.
.Bf -symbolic
Unlike previous signal facilities, the handler
func() remains installed after a signal has been delivered.
.Ef
.Pp
For some system calls, if a signal is caught while the call is
executing and the call is prematurely terminated,
the call is automatically restarted.
(The handler is installed using the
.Dv SA_RESTART
flag with
.Xr sigaction 2 . )
The affected system calls include
.Xr read 2 ,
.Xr write 2 ,
.Xr sendto 2 ,
.Xr recvfrom 2 ,
.Xr sendmsg 2
and
.Xr recvmsg 2
on a communications channel or a low speed device
and during a
.Xr ioctl 2
or
.Xr wait 2 .
However, calls that have already committed are not restarted,
but instead return a partial success (for example, a short read count).
This semantics could be changed with
.Xr siginterrupt 3 .
.Pp
When a process which has installed signal handlers forks,
the child process inherits the signals.
All caught signals may be reset to their default action by a call
to the
.Xr execve 2
function;
ignored signals remain ignored.
.Pp
See
.Xr sigaction 2
for a list of functions
that are considered safe for use in signal handler.
.Sh RETURN VALUES
The previous action is returned on a successful call.
Otherwise, SIG_ERR is returned and  the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn Signal
will fail and no action will take place if one of the
following occur:
.Bl -tag -width Er
.It Bq Er EINVAL
.Em Sig
is not a valid signal number.
.It Bq Er EINVAL
An attempt is made to ignore or supply a handler for
.Dv SIGKILL
or
.Ev SIGSTOP .
.El
.Sh SEE ALSO
.Xr kill 1 ,
.Xr kill 2 ,
.Xr ptrace 2 ,
.Xr sigaction 2 ,
.Xr sigaltstack 2 ,
.Xr sigprocmask 2 ,
.Xr sigsuspend 2 ,
.Xr fpsetmask 3 ,
.Xr setjmp 3 ,
.Xr siginterrupt 3 ,
.Xr tty 4
.Sh HISTORY
This
.Fn signal
facility appeared in
.Bx 4.0 .
Commit	Line	Data
5b2abdfb A	1	.\" Copyright (c) 1980, 1991, 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	.\" @(#)signal.3 8.3 (Berkeley) 4/19/94
	33	.\" $FreeBSD: src/lib/libc/gen/signal.3,v 1.28 2001/10/01 16:08:51 ru Exp $
	34	.\"
	35	.Dd April 19, 1994
	36	.Dt SIGNAL 3
	37	.Os
	38	.Sh NAME
	39	.Nm signal
	40	.Nd simplified software signal facilities
	41	.Sh LIBRARY
	42	.Lb libc
	43	.Sh SYNOPSIS
	44	.In signal.h
	45	.\" The following is Quite Ugly, but syntactically correct. Don't try to
	46	.\" fix it.
	47	.Ft void \(lp
	48	.Fn signal "int sig" "void \(lpfunc\(rp\(lpint\(rp\(rp\(rp\(lpint"
	49	.Pp
	50	or in
	51	.Fx Ns 's
	52	equivalent but easier to read typedef'd version:
	53	.Ft typedef "void \(lpsig_t\(rp \(lpint\*(rp"
	54	.Ft sig_t
	55	.Fn signal "int sig" "sig_t func"
	56	.Sh DESCRIPTION
	57	This
	58	.Fn signal
	59	facility
	60	is a simplified interface to the more general
	61	.Xr sigaction 2
	62	facility.
	63	.Pp
	64	Signals allow the manipulation of a process from outside its
65	domain as well as allowing the process to manipulate itself or
66	copies of itself (children). There are two general types of signals:
67	those that cause termination of a process and those that do not.
68	Signals which cause termination of a program might result from
69	an irrecoverable error or might be the result of a user at a terminal
70	typing the `interrupt' character.
71	Signals are used when a process is stopped because it wishes to access
72	its control terminal while in the background (see
73	.Xr tty 4 ) .
74	Signals are optionally generated
75	when a process resumes after being stopped,
76	when the status of child processes changes,
77	or when input is ready at the control terminal.
78	Most signals result in the termination of the process receiving them
79	if no action
80	is taken; some signals instead cause the process receiving them
81	to be stopped, or are simply discarded if the process has not
82	requested otherwise.
83	Except for the
84	.Dv SIGKILL
85	and
86	.Dv SIGSTOP
87	signals, the
88	.Fn signal
89	function allows for a signal to be caught, to be ignored, or to generate
90	an interrupt.
91	These signals are defined in the file
92	.Aq Pa signal.h :
93	.Bl -column SIGVTALARMXX "create core imagexxx"
94	.It Sy "Name Default Action Description"
95	.It Dv SIGHUP Ta "terminate process" Ta "terminal line hangup"
96	.It Dv SIGINT Ta "terminate process" Ta "interrupt program"
97	.It Dv SIGQUIT Ta "create core image" Ta "quit program"
98	.It Dv SIGILL Ta "create core image" Ta "illegal instruction"
99	.It Dv SIGTRAP Ta "create core image" Ta "trace trap"
100	.It Dv SIGABRT Ta "create core image" Ta "abort program"
101	(formerly
102	.Dv SIGIOT )
103	.It Dv SIGEMT Ta "create core image" Ta "emulate instruction executed"
104	.It Dv SIGFPE Ta "create core image" Ta "floating-point exception"
105	.It Dv SIGKILL Ta "terminate process" Ta "kill program"
106	.It Dv SIGBUS Ta "create core image" Ta "bus error"
107	.It Dv SIGSEGV Ta "create core image" Ta "segmentation violation"
108	.It Dv SIGSYS Ta "create core image" Ta "non-existent system call invoked"
109	.It Dv SIGPIPE Ta "terminate process" Ta "write on a pipe with no reader"
110	.It Dv SIGALRM Ta "terminate process" Ta "real-time timer expired"
111	.It Dv SIGTERM Ta "terminate process" Ta "software termination signal"
112	.It Dv SIGURG Ta "discard signal" Ta "urgent condition present on socket"
113	.It Dv SIGSTOP Ta "stop process" Ta "stop (cannot be caught or ignored)"
114	.It Dv SIGTSTP Ta "stop process" Ta "stop signal generated from keyboard"
115	.It Dv SIGCONT Ta "discard signal" Ta "continue after stop"
116	.It Dv SIGCHLD Ta "discard signal" Ta "child status has changed"
117	.It Dv SIGTTIN Ta "stop process" Ta "background read attempted from control terminal"
118	.It Dv SIGTTOU Ta "stop process" Ta "background write attempted to control terminal"
119	.It Dv SIGIO Ta "discard signal" Ta Tn "I/O"
120	is possible on a descriptor (see
121	.Xr fcntl 2 )
122	.It Dv SIGXCPU Ta "terminate process" Ta "cpu time limit exceeded (see"
123	.Xr setrlimit 2 )
124	.It Dv SIGXFSZ Ta "terminate process" Ta "file size limit exceeded (see"
125	.Xr setrlimit 2 )
126	.It Dv SIGVTALRM Ta "terminate process" Ta "virtual time alarm (see"
127	.Xr setitimer 2 )
128	.It Dv SIGPROF Ta "terminate process" Ta "profiling timer alarm (see"
129	.Xr setitimer 2 )
130	.It Dv SIGWINCH Ta "discard signal" Ta "Window size change"
131	.It Dv SIGINFO Ta "discard signal" Ta "status request from keyboard"
132	.It Dv SIGUSR1 Ta "terminate process" Ta "User defined signal 1"
133	.It Dv SIGUSR2 Ta "terminate process" Ta "User defined signal 2"
134	.El
135	.Pp
136	The
137	.Fa sig
138	parameter specifies which signal was received.
139	The
140	.Fa func
141	procedure allows a user to choose the action upon receipt of a signal.
142	To set the default action of the signal to occur as listed above,
143	.Fa func
144	should be
145	.Dv SIG_DFL .
146	A
147	.Dv SIG_DFL
148	resets the default action.
149	To ignore the signal
150	.Fa func
151	should be
152	.Dv SIG_IGN .
153	This will cause subsequent instances of the signal to be ignored
154	and pending instances to be discarded.
155	If
156	.Dv SIG_IGN
157	is not used,
158	further occurrences of the signal are
159	automatically blocked and
160	.Fa func
161	is called.
162	.Pp
163	The handled signal is unblocked when the
164	function returns and
165	the process continues from where it left off when the signal occurred.
166	.Bf -symbolic
167	Unlike previous signal facilities, the handler
168	func() remains installed after a signal has been delivered.
169	.Ef
170	.Pp
171	For some system calls, if a signal is caught while the call is
172	executing and the call is prematurely terminated,
173	the call is automatically restarted.
174	(The handler is installed using the
175	.Dv SA_RESTART
176	flag with
177	.Xr sigaction 2 . )
178	The affected system calls include
179	.Xr read 2 ,
180	.Xr write 2 ,
181	.Xr sendto 2 ,
182	.Xr recvfrom 2 ,
183	.Xr sendmsg 2
184	and
185	.Xr recvmsg 2
186	on a communications channel or a low speed device
187	and during a
188	.Xr ioctl 2
189	or
190	.Xr wait 2 .
191	However, calls that have already committed are not restarted,
192	but instead return a partial success (for example, a short read count).
193	This semantics could be changed with
194	.Xr siginterrupt 3 .
195	.Pp
196	When a process which has installed signal handlers forks,
197	the child process inherits the signals.
198	All caught signals may be reset to their default action by a call
199	to the
200	.Xr execve 2
201	function;
202	ignored signals remain ignored.
203	.Pp
204	See
205	.Xr sigaction 2
206	for a list of functions
207	that are considered safe for use in signal handler.
208	.Sh RETURN VALUES
209	The previous action is returned on a successful call.
210	Otherwise, SIG_ERR is returned and the global variable
211	.Va errno
212	is set to indicate the error.
213	.Sh ERRORS
214	.Fn Signal
215	will fail and no action will take place if one of the
216	following occur:
217	.Bl -tag -width Er
218	.It Bq Er EINVAL
219	.Em Sig
220	is not a valid signal number.
221	.It Bq Er EINVAL
222	An attempt is made to ignore or supply a handler for
223	.Dv SIGKILL
224	or
225	.Ev SIGSTOP .
226	.El
227	.Sh SEE ALSO
228	.Xr kill 1 ,
229	.Xr kill 2 ,
230	.Xr ptrace 2 ,
231	.Xr sigaction 2 ,
232	.Xr sigaltstack 2 ,
233	.Xr sigprocmask 2 ,
234	.Xr sigsuspend 2 ,
235	.Xr fpsetmask 3 ,
236	.Xr setjmp 3 ,
237	.Xr siginterrupt 3 ,
238	.Xr tty 4
239	.Sh HISTORY
240	This
241	.Fn signal
242	facility appeared in
243	.Bx 4.0 .