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.\" 34.Dd April 19, 1994 35.Dt SIGNAL 3 36.Os BSD 4 37.Sh NAME 38.Nm signal 39.Nd simplified software signal facilities 40.Sh SYNOPSIS 41.Fd #include <signal.h> 42.\" The following is Quite Ugly, but syntactically correct. Don't try to 43.\" fix it. 44.Ft void \*(lp* 45.Fn signal "int sig" "void \*(lp*func\*(rp\*(lpint\*(rp\*(rp\*(rp\*(lpint" 46 47or in FreeBSD's equivalent but easier to read typedef'd version: 48.Ft typedef "void \*(lp*sig_t\*(rp \*(lpint\*(rp" 49.Ft sig_t 50.Fn signal "int sig" "sig_t func" 51.Sh DESCRIPTION 52This 53.Fn signal 54facility 55is a simplified interface to the more general 56.Xr sigaction 2 57facility. 58.Pp 59Signals allow the manipulation of a process from outside its 60domain as well as allowing the process to manipulate itself or 61copies of itself (children). There are two general types of signals: 62those that cause termination of a process and those that do not. 63Signals which cause termination of a program might result from 64an irrecoverable error or might be the result of a user at a terminal 65typing the `interrupt' character. 66Signals are used when a process is stopped because it wishes to access 67its control terminal while in the background (see 68.Xr tty 4 ) . 69Signals are optionally generated 70when a process resumes after being stopped, 71when the status of child processes changes, 72or when input is ready at the control terminal. 73Most signals result in the termination of the process receiving them 74if no action 75is taken; some signals instead cause the process receiving them 76to be stopped, or are simply discarded if the process has not 77requested otherwise. 78Except for the 79.Dv SIGKILL 80and 81.Dv SIGSTOP 82signals, the 83.Fn signal 84function allows for a signal to be caught, to be ignored, or to generate 85an interrupt. 86These signals are defined in the file 87.Aq Pa signal.h : 88.Bl -column SIGVTALARMXX "create core imagexxx" 89.It Sy " Name " " Default Action " " Description" 90.It Dv SIGHUP No " terminate process" " terminal line hangup" 91.It Dv SIGINT No " terminate process" " interrupt program" 92.It Dv SIGQUIT No " create core image" " quit program" 93.It Dv SIGILL No " create core image" " illegal instruction" 94.It Dv SIGTRAP No " create core image" " trace trap" 95.It Dv SIGABRT No " create core image" Xr abort 2 96call (formerly 97.Dv SIGIOT ) 98.It Dv SIGEMT No " create core image" " emulate instruction executed" 99.It Dv SIGFPE No " create core image" " floating-point exception" 100.It Dv SIGKILL No " terminate process" " kill program" 101.It Dv SIGBUS No " create core image" " bus error" 102.It Dv SIGSEGV No " create core image" " segmentation violation" 103.It Dv SIGSYS No " create core image" " non-existent system call invoked" 104.It Dv SIGPIPE No " terminate process" " write on a pipe with no reader" 105.It Dv SIGALRM No " terminate process" " real-time timer expired" 106.It Dv SIGTERM No " terminate process" " software termination signal" 107.It Dv SIGURG No " discard signal" " urgent condition present on socket" 108.It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)" 109.It Dv SIGTSTP No " stop process" " stop signal generated from keyboard" 110.It Dv SIGCONT No " discard signal" " continue after stop" 111.It Dv SIGCHLD No " discard signal" " child status has changed" 112.It Dv SIGTTIN No " stop process" " background read attempted from control terminal" 113.It Dv SIGTTOU No " stop process" " background write attempted to control terminal" 114.It Dv SIGIO No " discard signal" Tn " I/O" 115is possible on a descriptor (see 116.Xr fcntl 2 ) 117.It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see" 118.Xr setrlimit 2 ) 119.It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see" 120.Xr setrlimit 2 ) 121.It Dv SIGVTALRM No " terminate process" " virtual time alarm (see" 122.Xr setitimer 2 ) 123.It Dv SIGPROF No " terminate process" " profiling timer alarm (see" 124.Xr setitimer 2 ) 125.It Dv SIGWINCH No " discard signal" " Window size change" 126.It Dv SIGINFO No " discard signal" " status request from keyboard" 127.It Dv SIGUSR1 No " terminate process" " User defined signal 1" 128.It Dv SIGUSR2 No " terminate process" " User defined signal 2" 129.El 130.Pp 131The 132.Fa sig 133parameter specifies which signal was received. 134The 135.Fa func 136procedure allows a user to choose the action upon receipt of a signal. 137To set the default action of the signal to occur as listed above, 138.Fa func 139should be 140.Dv SIG_DFL . 141A 142.Dv SIG_DFL 143resets the default action. 144To ignore the signal 145.Fa func 146should be 147.Dv SIG_IGN . 148This will cause subsequent instances of the signal to be ignored 149and pending instances to be discarded. If 150.Dv SIG_IGN 151is not used, 152further occurrences of the signal are 153automatically blocked and 154.Fa func 155is called. 156.Pp 157The handled signal is unblocked when the 158function returns and 159the process continues from where it left off when the signal occurred. 160.Bf -symbolic 161Unlike previous signal facilities, the handler 162func() remains installed after a signal has been delivered. 163.Ef 164.Pp 165For some system calls, if a signal is caught while the call is 166executing and the call is prematurely terminated, 167the call is automatically restarted. 168(The handler is installed using the 169.Dv SA_RESTART 170flag with 171.Xr sigaction 2 . ) 172The affected system calls include 173.Xr read 2 , 174.Xr write 2 , 175.Xr sendto 2 , 176.Xr recvfrom 2 , 177.Xr sendmsg 2 178and 179.Xr recvmsg 2 180on a communications channel or a low speed device 181and during a 182.Xr ioctl 2 183or 184.Xr wait 2 . 185However, calls that have already committed are not restarted, 186but instead return a partial success (for example, a short read count). 187.Pp 188When a process which has installed signal handlers forks, 189the child process inherits the signals. 190All caught signals may be reset to their default action by a call 191to the 192.Xr execve 2 193function; 194ignored signals remain ignored. 195.Sh RETURN VALUES 196The previous action is returned on a successful call. 197Otherwise, \-1 is returned and the global variable 198.Va errno 199is set to indicate the error. 200.Sh ERRORS 201.Fn Signal 202will fail and no action will take place if one of the 203following occur: 204.Bl -tag -width [EINVAL] 205.It Bq Er EINVAL 206.Em Sig 207is not a valid signal number. 208.It Bq Er EINVAL 209An attempt is made to ignore or supply a handler for 210.Dv SIGKILL 211or 212.Ev SIGSTOP . 213.Sh SEE ALSO 214.Xr kill 1 , 215.Xr kill 2 , 216.Xr ptrace 2 , 217.Xr sigaction 2 , 218.Xr sigaltstack 2 , 219.Xr sigprocmask 2 , 220.Xr sigsuspend 2 , 221.Xr setjmp 3 , 222.Xr tty 4 223.Sh HISTORY 224This 225.Nm signal 226facility appeared in 227.Bx 4.0 . 228