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Annotation of researchv10dc/man/man2/signal.2, revision 1.1

1.1     ! root        1: .TH SIGNAL 2
        !             2: .CT 2 proc_man
        !             3: .SH NAME
        !             4: signal, kill \(mi receive and send signals
        !             5: .SH SYNOPSIS
        !             6: .nf
        !             7: .B #include <signal.h>
        !             8: .PP
        !             9: .B SIG_TYP signal(sig, func)
        !            10: .B SIG_TYP func;
        !            11: .PP
        !            12: .B int kill(pid, sig)
        !            13: .fi
        !            14: .SH DESCRIPTION
        !            15: A signal
        !            16: is generated by some abnormal event
        !            17: initiated by a user at a terminal (quit, interrupt),
        !            18: by a program error (bus error, etc.),
        !            19: or by
        !            20: .I kill
        !            21: in another process.
        !            22: Normally, most signals
        !            23: cause termination of the receiving process,
        !            24: but
        !            25: .I signal
        !            26: allows them either to be ignored
        !            27: or to be caught by interrupting to a specified function.
        !            28: The following signal names are defined in
        !            29: .FR <signal.h> :
        !            30: .LP
        !            31: .nf
        !            32: .ta \w'SIGMMMM 'u +\w'15*  'u
        !            33: \fLSIGHUP\fP   1       hangup
        !            34: \fLSIGINT\fP   2       interrupt
        !            35: \fLSIGQUIT\fP  3*      quit
        !            36: \fLSIGILL\fP   4*      illegal instruction (not reset when caught)
        !            37: \fLSIGTRAP\fP  5*      trace trap (not reset when caught)
        !            38: \fLSIGIOT\fP   6*      IOT instruction
        !            39: \fLSIGEMT\fP   7*      EMT instruction
        !            40: \fLSIGFPE\fP   8*      floating point exception
        !            41: \fLSIGKILL\fP  9       kill (cannot be caught or ignored)
        !            42: \fLSIGBUS\fP   10*     bus error
        !            43: \fLSIGSEGV\fP  11*     segmentation violation
        !            44: \fLSIGSYS\fP   12*     bad argument to system call
        !            45: \fLSIGPIPE\fP  13      write on a pipe with no one to read it
        !            46: \fLSIGALRM\fP  14      alarm clock
        !            47: \fLSIGTERM\fP  15      software termination signal
        !            48:        16      unassigned
        !            49: \fLSIGSTOP\fP  17+     stop (cannot be caught or ignored)
        !            50: \fLSIGCONT\fP  19#     continue a stopped process
        !            51: \fLSIGCHLD\fP  20#     child has stopped or exited
        !            52: .sp
        !            53: .fi
        !            54: *      places core image in file
        !            55: .B core
        !            56: if not caught or ignored
        !            57: .br
        !            58: +      suspends process until
        !            59: .B SIGCONT
        !            60: or
        !            61: .BR PIOCRUN ;
        !            62: see
        !            63: .IR proc (4)
        !            64: .br
        !            65: #      ignored if not caught
        !            66: .PP
        !            67: Signals 1 through
        !            68: .BR NSIG -1,
        !            69: defined in the include file, exist.
        !            70: Those not listed above have
        !            71: no conventional meaning in this system.
        !            72: (Berkeley systems use 1-15 and 17-25.)
        !            73: .PP
        !            74: .I Signal
        !            75: specifies how signal
        !            76: .I sig
        !            77: will be handled.
        !            78: If
        !            79: .I func
        !            80: is
        !            81: .BR SIG_DFL ,
        !            82: the default action listed above is reinstated.
        !            83: If
        !            84: .I func
        !            85: is
        !            86: .BR SIG_IGN ,
        !            87: the signal will be ignored.
        !            88: Otherwise, when the signal occurs, it will be caught and
        !            89: a function, pointed to by
        !            90: .IR func ,
        !            91: will be called.  
        !            92: The type of pointer
        !            93: .I func
        !            94: is 
        !            95: .BR SIG_TYP :
        !            96: .IP
        !            97: .B typedef int (*SIG_TYP)();
        !            98: .LP
        !            99: It must point to a function such as,
        !           100: .EX
        !           101: .L
        !           102:         int catcher(sig) { ... }
        !           103: .EE
        !           104: which will be called with a
        !           105: signal number as argument.
        !           106: A return from the catcher function will
        !           107: continue the process at the point it was interrupted.
        !           108: .PP
        !           109: Except as indicated, a signal is reset to
        !           110: .B SIG_DFL
        !           111: after being caught.
        !           112: Thus if it is desired to catch every such signal,
        !           113: the catching routine must issue another
        !           114: .I signal
        !           115: call.
        !           116: .PP
        !           117: When a caught signal occurs
        !           118: during certain system calls, the call terminates prematurely.
        !           119: In particular this can occur during
        !           120: .IR read (2)
        !           121: or
        !           122: .IR write
        !           123: on a slow device (like a typewriter, but not a disk),
        !           124: and during
        !           125: .IR pause 
        !           126: and
        !           127: .IR wait ;
        !           128: see
        !           129: .IR alarm (2)
        !           130: and
        !           131: .IR exit (2).
        !           132: The interrupted system call will return error
        !           133: .BR EINTR .
        !           134: The user's program may then, if it wishes, re-execute the call.
        !           135: .PP
        !           136: .I Signal
        !           137: returns the previous (or initial)
        !           138: value of
        !           139: .I func
        !           140: for the particular signal.
        !           141: .PP
        !           142: After a
        !           143: .IR  fork (2)
        !           144: the child inherits all signal settings.
        !           145: .IR  Exec (2)
        !           146: resets all caught signals to default action.
        !           147: .PP
        !           148: .I Kill
        !           149: sends signal
        !           150: .I sig
        !           151: to the process specified by process id
        !           152: .I pid.
        !           153: Signal 0
        !           154: has no effect on the target process and may be used to
        !           155: test the existence of a process.
        !           156: The success of sending a signal is independent of how the receiving
        !           157: process treats the signal.
        !           158: .PP
        !           159: The effective userid of the sending process must be either 0
        !           160: or the effective userid of the receiving process.
        !           161: .PP
        !           162: If
        !           163: .I pid
        !           164: is 0, the signal is sent to all other processes in the
        !           165: sender's process group; see
        !           166: .IR stream (4).
        !           167: .PP
        !           168: If
        !           169: .I pid
        !           170: is \-1, and the user is the super-user,
        !           171: the signal is broadcast universally
        !           172: except to processes 0 (scheduler),
        !           173: 1 (initialization)
        !           174: and 2 (pageout); see
        !           175: .IR init (8).
        !           176: If
        !           177: .I pid
        !           178: is less than \-1,
        !           179: it is negated
        !           180: and taken as a process group
        !           181: whose members should receive the signal.
        !           182: .PP
        !           183: Processes may send signals to themselves.
        !           184: .SH FILES
        !           185: .F core
        !           186: .SH "SEE ALSO"
        !           187: .IR kill (1),
        !           188: .IR setjmp (3),
        !           189: .IR stream (4)
        !           190: .SH DIAGNOSTICS
        !           191: .IR signal :
        !           192: .B EINVAL
        !           193: .br
        !           194: .IR kill :
        !           195: .BR EINVAL ,
        !           196: .BR EPERM ,
        !           197: .BR ESRCH
        !           198: .SH BUGS
        !           199: The reason for a trap should be distinguishable by extra arguments
        !           200: to the signal handler.
        !           201: .br
        !           202: If a repeated signal arrives before the last one can be reset,
        !           203: there is no chance to catch it.
        !           204: .br
        !           205: For historical reasons, the return value of
        !           206: a catcher function is
        !           207: .BR int ;
        !           208: it is 
        !           209: .B void
        !           210: in 
        !           211: .SM ANSI
        !           212: standard C.

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