.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\" @(#)sigvec.2 6.1 (Berkeley) %G%
sigvec \- software signal facilities
.B sigvec(sig, vec, ovec)
.B struct sigvec *vec, *ovec;
The system defines a set of signals that may be delivered to a process.
Signal delivery resembles the occurence of a hardware interrupt:
the signal is blocked from further occurrence, the current process
context is saved, and a new one is built. A process may specify a
to which a signal is delivered, or specify that a signal is to be
A process may also specify that a default action is to be taken
by the system when a signal occurs.
Normally, signal handlers execute on the current stack
of the process. This may be changed, on a per-handler basis,
so that signals are taken on a special
All signals have the same
Signal routines execute with the signal that caused their
but other signals may yet occur.
defines the set of signals currently blocked from delivery
to a process. The signal mask for a process is initialized
from that of its parent (normally 0). It
call, or when a signal is delivered to the process.
condition arises for a process, the signal is added to a set of
signals pending for the process. If the signal is not currently
by the process then it is delivered to the process. When a signal
is delivered, the current state of the process is saved,
a new signal mask is calculated (as described below),
and the signal handler is invoked. The call to the handler
is arranged so that if the signal handling routine returns
normally the process will resume execution in the context
from before the signal's delivery.
If the process wishes to resume in a different context, then it
must arrange to restore the previous context itself.
When a signal is delivered to a process a new signal mask is
installed for the duration of the process' signal handler
This mask is formed by taking the current signal mask,
adding the signal to be delivered, and
in the signal mask associated with the handler to be invoked.
assigns a handler for a specific signal. If
specifies a handler routine and mask
to be used when delivering the specified signal.
Further, if the SV_ONSTACK bit is set in
the system will deliver the signal to the process on a
is non-zero, the previous handling information for the signal
The following is a list of all signals
with names as in the include file
.ta \w'SIGVTALRM 'u +\w'15* 'u
SIGILL 4* illegal instruction
SIGIOT 6* IOT instruction
SIGEMT 7* EMT instruction
SIGFPE 8* floating point exception
SIGKILL 9 kill (cannot be caught, blocked, or ignored)
SIGSEGV 11* segmentation violation
SIGSYS 12* bad argument to system call
SIGPIPE 13 write on a pipe with no one to read it
SIGTERM 15 software termination signal
SIGURG 16\*b urgent condition present on socket
SIGSTOP 17\*d stop (cannot be caught, blocked, or ignored)
SIGTSTP 18\*d stop signal generated from keyboard
SIGCONT 19\*b continue after stop (cannot be blocked)
SIGCHLD 20\*b child status has changed
SIGTTIN 21\*d background read attempted from control terminal
SIGTTOU 22\*d background write attempted to control terminal
SIGIO 23\*b i/o is possible on a descriptor (see \fIfcntl\fP(2))
SIGXCPU 24 cpu time limit exceeded (see \fIsetrlimit\fP(2))
SIGXFSZ 25 file size limit exceeded (see \fIsetrlimit\fP(2))
SIGVTALRM 26 virtual time alarm (see \fIsetitimer\fP(2))
SIGPROF 27 profiling timer alarm (see \fIsetitimer\fP(2))
SIGWINCH 28\*b window size change
The starred signals in the list above cause a core image
if not caught or ignored.
Once a signal handler is installed, it remains installed
The default action for a signal may be reinstated by setting
to SIG_DFL; this default is termination
(with a core image for starred signals)
except for signals marked with \*b or \*d.
Signals marked with \*b are discarded if the action
is SIG_DFL; signals marked
with \*d cause the process to stop.
is SIG_IGN the signal is subsequently ignored,
and pending instances of the signal are discarded.
If a caught signal occurs during certain system calls,
the call is normally restarted.
The call can be forced to terminate prematurely with an
EINTR error return by setting the SV_INTERRUPT bit in
The affected system calls are
on a slow device (such as a terminal; but not a file)
all signals, the signal mask, the signal stack,
and the restart/interrupt flags.
caught signals to default action and
resets all signals to be caught on the user stack.
Ignored signals remain ignored;
the signal mask remains the same;
signals that interrupt system calls continue to do so.
is not allowed to block SIGKILL, SIGSTOP, or SIGCONT. This
is done silently by the system.
The SV_INTERRUPT flag is not available in 4.2BSD,
hence it should not be used if backward compatibility is needed.
A 0 value indicated that the call succeeded. A \-1 return value
indicates an error occurred and
is set to indicated the reason.
will fail and no new signal handler will be installed if one
points to memory which is not a valid part of the process
is not a valid signal number.
An attempt is made to ignore or supply a handler for SIGKILL
An attempt is made to ignore SIGCONT (by default SIGCONT
sigblock(2), sigsetmask(2), sigpause(2),
sigstack(2), sigvec(2), setjmp(3), siginterrupt(3), tty(4)
The handler routine can be declared:
is the signal number, into which the hardware faults and traps are
is a parameter which is either a constant
as given below or, for compatibility mode faults, the code provided by
the hardware (Compatibility mode faults are distinguished from the
other SIGILL traps by having PSL_CM set in the psl).
used to restore the context from before the signal.
The following defines the mapping of hardware traps to signals
and codes. All of these symbols are defined in
.ta \w' Floating/decimal divide by zero 'u +\w'15* 'u +8n
Hardware condition Signal Code
Integer overflow SIGFPE FPE_INTOVF_TRAP
Integer division by zero SIGFPE FPE_INTDIV_TRAP
Floating overflow trap SIGFPE FPE_FLTOVF_TRAP
Floating/decimal division by zero SIGFPE FPE_FLTDIV_TRAP
Floating underflow trap SIGFPE FPE_FLTUND_TRAP
Decimal overflow trap SIGFPE FPE_DECOVF_TRAP
Subscript-range SIGFPE FPE_SUBRNG_TRAP
Floating overflow fault SIGFPE FPE_FLTOVF_FAULT
Floating divide by zero fault SIGFPE FPE_FLTDIV_FAULT
Floating underflow fault SIGFPE FPE_FLTUND_FAULT
Length access control SIGSEGV
Protection violation SIGBUS
Reserved instruction SIGILL ILL_RESAD_FAULT
Customer-reserved instr. SIGEMT
Reserved operand SIGILL ILL_PRIVIN_FAULT
Reserved addressing SIGILL ILL_RESOP_FAULT
Compatibility-mode SIGILL hardware supplied code
This manual page is still confusing.
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