380 lines
8.3 KiB
Plaintext
380 lines
8.3 KiB
Plaintext
is assigned one of three values:
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.BR \s-1SIG_DFL\s+1
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or
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.BR \s-1SIG_IGN\s+1 ,
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which are macros (defined in
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.IR <sys/signal.h> )
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that expand to constant expressions,
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or a
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.IR "function address" .
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.PP
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The actions prescribed by its value are as follows:
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.RS 2
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.PP
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.SM
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.B SIG_DFL
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\&\- terminate process upon receipt of a signal
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.RS 8
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Upon receipt of the signal
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.IR sig ,
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the receiving process is to be terminated with all of the consequences outlined
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in
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.IR exit (2).
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See \s-1SIGNAL NOTES [\s01\s-1]\s0 below.
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.RE
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.PP
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.SM
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.B SIG_IGN
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\&\- ignore signal
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.RS 8
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The signal
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.I sig\^
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is to be ignored.
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.PP
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Note: the signals
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.B
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.SM SIGKILL,
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.B
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.SM SIGSTOP
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and
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.B
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.SM SIGCONT
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cannot be ignored.
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.RE
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.PP
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.I function address\^
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\&\- catch signal
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.RS 8
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Upon receipt of the signal
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.IR sig ,
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the receiving process is to execute the signal-catching function whose
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address is specified via this parameter.
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The function will be invoked as follows:
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.PP
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.RS
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.nf
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.B "handler (int sig, int code, struct sigcontext \(**sc);"
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.fi
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.RE
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.PP
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Where
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.I handler
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is the specified function-name.
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.I code\^
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is valid only in the following cases:
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.PP
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.ta \w' Floating/decimal divide by zero 'u +\w'15* 'u +8n
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.nf
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Condition Signal Code
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User breakpoint SIGTRAP BRK_USERBP
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User breakpoint SIGTRAP BRK_SSTEPBP
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Integer overflow SIGTRAP BRK_OVERFLOW
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Divide by zero SIGTRAP BRK_DIVZERO
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Multiply overflow SIGTRAP BRK_MULOVF
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Invalid virtual address SIGSEGV EFAULT
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Read-only address SIGSEGV EACCES
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Read beyond mapped object SIGSEGV ENXIO
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.fi
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.PP
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The third argument
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.I sc\^
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is a pointer to a
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.I struct sigcontext (defined in <\f2sys/signal.h\f1>)
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that contains the processor context at the time of the signal.
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.Op f
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The \s-1FORTRAN\s+1 arguments are defined in the same way except for
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the last argument
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which can be defined either as an array of integers or as a record.
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.Op
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.PP
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Upon return from the signal-catching function, the receiving process will
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resume execution at the point it was interrupted.
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.PP
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Before entering the signal-catching function, the value of
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.I func\^
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for the caught signal will be set to
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.SM
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.B SIG_DFL
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unless the signal is
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.SM
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.BR SIGILL ,
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.SM
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.BR SIGTRAP ", or"
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.SM
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.BR SIGPWR .
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This means that before exiting the handler, a
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.I signal
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call is necessary to again set the disposition to catch the
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signal.
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.PP
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When a signal that is to be caught occurs during a
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.IR read "(2), a" " write" (2),
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.RI an " open" "(2), or an " ioctl (2)\^
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system call on a slow device (like a terminal; but not a file), during a
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.IR pause (2)
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system call, or during a
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.IR wait (2)
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system call that does not return immediately due to the existence of a
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previously stopped or zombie
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process, the signal catching function will be executed and then the
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interrupted system call may return a \-1 to the calling process with
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.I errno\^
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set to \f3\s-1EINTR\s+1\fP.
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.PP
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Note: The signals
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.B
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.SM SIGKILL
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and
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.B
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.SM SIGSTOP
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cannot be caught.
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.RE
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.RE
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.SH SIGNAL NOTES
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.TP 4
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.B [1]
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If
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.SM
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.B SIG_DFL
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is assigned for these signals, in addition to the process being terminated,
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a ``core image'' will be constructed in the current working directory of the process, if the following conditions are met:
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.RS 4
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.RS 8
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.PP
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The effective user
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.SM ID
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and the real user
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.SM ID
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of the receiving
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process are equal.
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.PP
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An ordinary file named
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.B core
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exists and is writable or can be created.
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If the file must be created, it will have the following properties:
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.RS 8
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.PP
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a mode of 0666 modified by the file creation mask
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.RI [see " umask" (2)]
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.PP
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a file owner
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.SM ID
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that is the same as the effective user
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.SM ID
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of the receiving process.
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.PP
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a file group
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.SM ID
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that is the same as the effective group
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.SM ID
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of the receiving process
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.RE
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.RE
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.RE
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.PP
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.SM
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.B NOTE:
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The core file may be truncated
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if the resultant file size would exceed either
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.I ulimit
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[see
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.IR ulimit (2)]
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or
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the process's maximum core file size [see
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.IR setrlimit (2)].
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.PP
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.TP 4
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.B [2]
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For the signals
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.BR \s-1SIGCLD\s+1 ,
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.BR \s-1SIGWINCH\s+1 ,
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.BR \s-1SIGPWR\s+1 ,
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.BR \s-1SIGURG\s+1 ,
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and
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.BR \s-1SIGIO\s+1 ,
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the handler parameter
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is assigned one of three values:
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.BR \s-1SIG_DFL\s+1 ,
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.BR \s-1SIG_IGN\s+1 ,
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or a
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.IR "function address".
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The actions prescribed by these values are:
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.RS 4
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.RS 2
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.PP
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.SM
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.B SIG_DFL
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\&\- ignore signal
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.RS 8
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The signal is to be ignored.
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.RE
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.PP
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.SM
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.B SIG_IGN
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\&\- ignore signal
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.RS 8
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The signal is to be ignored.
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Also, if
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.I sig\^
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is
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.SM
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.BR SIGCLD ,
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the calling process's child processes will not create zombie processes when
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they terminate
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[see \f2exit\f1(2)].
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.RE
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.PP
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.I function address\^
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\&\- catch signal
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.RS 8
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If the signal is
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.SM
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.BR \f3SIGPWR\fP ,
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.SM
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.BR \f3SIGURG\fP ,
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.SM
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.BR \f3SIGIO\fP ,
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or
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.SM
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.BR \f3SIGWINCH\fP ,
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the action to be taken is the same as that described above for
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a handler parameter
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equal to
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.IR "function address" .
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The same is true if the signal is
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.SM
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.B SIGCLD
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with one exception:
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while the process is executing the signal-catching function,
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all terminating child processes will be queued.
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The \f2wait\f1
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system call removes the first entry of the queue.
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If the
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.I signal
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system call is used to catch
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.SM
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.BR SIGCLD ,
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the signal handler must be re-attached when exiting the
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handler, and at that time--if the queue is not empty--\f3\s-1SIGCLD\s+1\fP
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is re-raised before \f2signal\f1 returns. See \f2wait\fP(2).
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.RE
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.RE
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.PP
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In addition,
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.SM
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.B SIGCLD
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affects
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the
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.IR wait " and " exit
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system calls as follows:
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.RS 2
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.TP 8
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.I wait\^
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If the
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handler parameter of
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.SM
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.B SIGCLD
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is set to
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.SM
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.B SIG_IGN
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and a
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.I wait\^
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is executed, the
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.I wait\^
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will block until all of the calling process's child processes terminate;
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it will then return a value of \-1 with
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.I errno\^
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set to \f3\s-1ECHILD\s+1\fP.
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.TP 8
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.I exit\^
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If in the exiting process's parent process the
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handler parameter of
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.SM
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.B SIGCLD
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is set to
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.SM
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.BR SIG_IGN ,
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the exiting process will not create a zombie process.
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.PP
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When processing a pipeline, the shell
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makes the last process in the pipeline the parent of the proceeding processes.
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A process that may be piped into in this manner (and thus become the parent
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of other processes) should take care not to set
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.SM
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.B SIGCLD
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to be caught.
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.RE
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.RE
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.PP
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.TP 4
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.B [3]
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.B \s-1SIGPOLL\s+1
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is issued when a file descriptor corresponding
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to a \s-1STREAMS\s0 [see \f2intro\f1(2)] file has a "selectable" event pending.
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A process must specifically request that this signal be sent
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using the \f3\s-1I_SETSIG\s0\fP \f2ioctl\fP call.
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Otherwise, the process will never receive
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.BR \s-1SIGPOLL\s+1 .
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.PP
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.TP 4
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.B [4]
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.B \s-1SIGEMT\s+1
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is never generated on an
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.B \s-1IRIS-4D\s+1
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system.
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.PP
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.TP 4
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.B [5]
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.B \s-1SIGTRAP\s+1
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is generated for breakpoint instructions, overflows, divide by zeros,
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range errors,
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and multiply overflows.
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The second argument
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.I code
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gives specific details of the cause of the signal.
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Possible values are described in <\f2sys/signal.h\f1>.
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.PP
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.TP 4
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.B [6]
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The signals \f3\s-1SIGSTOP\s+1\f1, \f3\s-1SIGTSTP\s+1\f1,
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\f3\s-1SIGTTIN\s+1\f1, \f3\s-1SIGTTOU\s+1\f1
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and \f3\s-1SIGCONT\s+1\f1 are used by command interpreters like the C shell
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[see \f2csh\f1(1)] to provide job control.
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The first four signals listed will cause the receiving process to be
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stopped, unless the signal is caught or ignored.
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\f3\s-1SIGCONT\s+1\f1 causes a stopped process to be resumed.
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\f3\s-1SIGTSTP\s+1\f1 is sent from the terminal driver in response
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to the
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.SM SWTCH
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character being entered from the keyboard [see \f2termio\f1(7)].
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\f3\s-1SIGTTIN\s+1\f1 is sent from the terminal driver when a background
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process attempts to read from its controlling terminal.
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If \f3\s-1SIGTTIN\s+1\f1 is ignored by the process, then the read will
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return \f3\s-1EIO\s+1\f1.
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\f3\s-1SIGTTOU\s+1\f1 is sent from the terminal driver when a background
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process attempts to write to its controlling terminal when the
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terminal is in \f3\s-1TOSTOP\s+1\f1 mode.
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If \f3\s-1SIGTTOU\s+1\f1 is ignored by the process, then the write will
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succeed regardless of the state of the controlling terminal.
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.Op f
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.SH EXAMPLES
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This is an example in \s-1FORTRAN\s+1:
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.nf
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#include <sys/signal.h>
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EXTERNAL FPROC
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INTEGER SIGNAL
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INTEGER CPADDR
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I = SIGNAL(SIGTERM, FPROC, -1)
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J = SIGNAL(SIGINT, 0, CPADDR)
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.fi
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The first call to \f2signal\f1 sets up the \s-1FORTRAN\s+1 function
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\f2fproc\f1 as the signal-handling routine for \f3\s-1SIGTERM\s+1\f1.
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The second call sets up a C function whose address is in the variable
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\f2cpaddr\f1 as the signal-handling routine for \f3\s-1SIGINT\s+1\f1.
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.Op
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