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.\" @(#)sigvec.2 6.7 (Berkeley) 4/29/91
.Nd software signal facilities
.Fn sigvec "int sig" "struct sigvec *vec" "struct sigvec *ovec"
This interface is made obsolete by sigaction(2).
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.
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
.Bl -column SIGVTALARMXX "create core imagexxx"
.It Sy " NAME " " Default Action " " Description"
.It Dv SIGHUP No " terminate process" " terminal line hangup"
.It Dv SIGINT No " terminate process" " interrupt program"
.It Dv SIGQUIT No " create core image" " quit program"
.It Dv SIGILL No " create core image" " illegal instruction"
.It Dv SIGTRAP No " create core image" " trace trap"
.It Dv SIGABRT No " create core image" Xr abort 2
.It Dv SIGEMT No " create core image" " emulate instruction executed"
.It Dv SIGFPE No " create core image" " floating-point exception"
.It Dv SIGKILL No " terminate process" " kill program"
.It Dv SIGBUS No " create core image" " bus error"
.It Dv SIGSEGV No " create core image" " segmentation violation"
.It Dv SIGSYS No " create core image" " system call given invalid argument"
.It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
.It Dv SIGALRM No " terminate process" " real-time timer expired"
.It Dv SIGTERM No " terminate process" " software termination signal"
.It Dv SIGURG No " discard signal" " urgent condition present on socket"
.It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
.It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
.It Dv SIGCONT No " discard signal" " continue after stop"
.It Dv SIGCHLD No " discard signal" " child status has changed"
.It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
.It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
.It Dv SIGIO No " discard signal" Tn " I/O"
is possible on a descriptor (see
.It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
.It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
.It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
.It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
.It Dv SIGWINCH No " discard signal" " Window size change"
.It Dv SIGINFO No " discard signal" " status request from keyboard"
.It Dv SIGUSR1 No " terminate process" " User defined signal 1"
.It Dv SIGUSR2 No " terminate process" " User defined signal 2"
Once a signal handler is installed, it remains installed
A signal-specific default action may be reset by
The defaults are process termination, possibly with core dump;
no action; stopping the process; or continuing the process.
See the above signal list for each signal's default action.
current and pending instances
of the signal are ignored and discarded.
If a signal is caught during the system calls listed below,
the call is normally restarted.
The call can be forced to terminate prematurely with an
error return by setting the
The affected system calls include
on a communications channel or a slow device (such as a terminal,
However, calls that have already committed are not restarted,
but instead return a partial success (for example, a short read count).
all signals, the signal mask, the signal stack,
and the restart/interrupt flags are inherited by the child.
action for all signals which were caught 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.
This is done silently by the system.
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 that 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
The handler routine can be declared:
.Bd -literal -offset indent
void handler(sig, code, scp)
is the signal number, into which the hardware faults and traps are
is a parameter that 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
used to restore the context from before the signal.
This manual page is still confusing.