projects / unix-history / blame
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|---|---|---|
| 944ae7c9 KM |
1 | .\" Copyright (c) 1983 Regents of the University of California. |
| 2 | .\" All rights reserved. The Berkeley software License Agreement | |
| 3 | .\" specifies the terms and conditions for redistribution. | |
| 4 | .\" | |
| 95f51977 | 5 | .\" @(#)signal.3f 6.1 (Berkeley) 5/15/85 |
| 944ae7c9 | 6 | .\" |
| 95f51977 | 7 | .TH SIGNAL 3F "May 15, 1985" |
| 944ae7c9 KM |
8 | .UC 5 |
| 9 | .SH NAME | |
| 10 | signal \- change the action for a signal | |
| 11 | .SH SYNOPSIS | |
| 12 | .B integer function signal(signum, proc, flag) | |
| 13 | .br | |
| 14 | .B integer signum, flag | |
| 15 | .br | |
| 16 | .B external proc | |
| 17 | .SH DESCRIPTION | |
| 18 | When a process incurs a signal (see | |
| 19 | .IR signal (3C)) | |
| 20 | the default action | |
| 21 | is usually to clean up and abort. | |
| 22 | The user may choose to write an alternative signal handling routine. | |
| 23 | A call to | |
| 24 | .I signal | |
| 25 | is the way this alternate action is specified to the system. | |
| 26 | .PP | |
| 27 | .I Signum | |
| 28 | is the signal number (see | |
| 29 | .IR signal (3C)). | |
| 30 | If | |
| 31 | .I flag | |
| 32 | is negative, then | |
| 33 | .I proc | |
| 34 | must be the name of the user signal handling routine. | |
| 35 | If | |
| 36 | .I flag | |
| 37 | is zero or positive, then | |
| 38 | .I proc | |
| 39 | is ignored and the value of | |
| 40 | .I flag | |
| 41 | is passed to the system as the signal action definition. | |
| 42 | In particular, this is how previously saved signal actions can be restored. | |
| 43 | Two possible values for | |
| 44 | .I flag | |
| 45 | have specific meanings: | |
| 46 | 0 means "use the default action" (See NOTES below), | |
| 47 | 1 means "ignore this signal". | |
| 48 | .PP | |
| 49 | A positive returned value is the previous action definition. | |
| 50 | A value greater than 1 is the address of a routine that | |
| 51 | was to have been called on occurrence of the given signal. | |
| 52 | The returned value can be used in subsequent calls to | |
| 53 | .I signal | |
| 54 | in order to restore a previous action definition. | |
| 55 | A negative returned value is the negation of a system error code. | |
| 56 | (See | |
| 57 | .IR perror (3F)) | |
| 58 | .SH FILES | |
| 59 | .ie \nM /usr/ucb/lib/libU77.a | |
| 60 | .el /usr/lib/libU77.a | |
| 61 | .SH "SEE ALSO" | |
| 62 | signal(3C), kill(3F), kill(1) | |
| 63 | .SH NOTES | |
| 64 | .B f77 | |
| 65 | arranges to trap certain signals when a process is started. | |
| 66 | The only way to restore the default | |
| 67 | .B f77 | |
| 68 | action is to save the returned | |
| 69 | value from the first call to | |
| 70 | .I signal. | |
| 71 | .PP | |
| 72 | If the user signal handler is called, it will be passed the signal number | |
| 73 | as an integer argument. |