signal(3-ucb) (BSD Compatibility Package) signal(3-ucb)
NAME
signal - simplified software signal facilities
SYNOPSIS
/usr/ucb/cc [flag ...] file ... -lucb
#include <signal.h>
void (*signal(sig, func))()
void (*func)();
DESCRIPTION
signal is a simplified interface to the more general sigvec(3) facil-
ity. Programs that use signal in preference to sigvec are more likely
to be portable to all systems.
A signal is generated by some abnormal event, initiated by a user at a
terminal (quit, interrupt, stop), by a program error (for example, bus
error), by request of another program (kill), or when a process is
stopped because it wishes to access its control terminal while in the
background [see termio(7)]. Signals are optionally generated when a
process resumes after being stopped, when the status of child
processes changes, or when input is ready at the control terminal.
Most signals cause termination of the receiving process if no action
is taken; some signals instead cause the process receiving them to be
stopped, or are simply discarded if the process has not requested oth-
erwise. Except for the SIGKILL and SIGSTOP signals, the signal call
allows signals either to be ignored or to interrupt to a specified
location. The following is a list of all signals with names as in the
include file <signal.h>:
SIGHUP Hangup
SIGINT Interrupt
SIGQUIT * Quit
SIGILL * Illegal instruction
SIGTRAP * Trace trap
SIGABRT * Abort (generated by abort(3C) routine)
SIGEMT * Emulator trap
SIGFPE * Arithmetic exception
SIGKILL Kill (cannot be caught, blocked, or ignored)
SIGBUS * Bus error
SIGSEGV * Segmentation violation
SIGSYS * Bad argument to system call
SIGPIPE Write on a pipe or other socket with no one to read it
SIGALRM Alarm clock
SIGTERM Software termination signal
SIGURG - Urgent condition present on socket
SIGSTOP + Stop (cannot be caught, blocked, or ignored)
SIGTSTP + Stop signal generated from keyboard
SIGCONT - Continue after stop (cannot be blocked)
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signal(3-ucb) (BSD Compatibility Package) signal(3-ucb)
SIGCHLD - Child status has changed
SIGTTIN + Background read attempted from control terminal
SIGTTOU + Background write attempted to control terminal
SIGIO - I/O is possible on a descriptor [see fcntl(2)]
SIGXCPU CPU time limit exceeded [see setrlimit(2)]
SIGXFSZ File size limit exceeded [see setrlimit(2)]
SIGVTALRM Virtual time alarm [see getitimer(3C)]
SIGPROF Profiling timer alarm [see getitimer(3C)]
SIGWINCH - Window changed [see termio(7)]
SIGUSR1 User-defined signal 1
SIGUSR2 User-defined signal 2
The starred signals ("*") in the list above cause a core image if not
caught or ignored.
If func is SIGDFL, the default action for signal sig is reinstated;
this default is termination (with a core image for starred signals)
except for signals marked with "-" or "+". Signals marked with "-" are
discarded if the action is SIGDFL; signals marked with "+" cause the
process to stop. If func is SIGIGN the signal is subsequently ignored
and pending instances of the signal are discarded. Otherwise, when the
signal occurs further occurrences of the signal are automatically
blocked and func is called.
A return from the function unblocks the handled signal and continues
the process at the point it was interrupted.
If a caught signal occurs during certain system calls, terminating the
call prematurely, the call is automatically restarted. In particular
this can occur during a read or write on a slow device (such as a ter-
minal; but not a file) and during a wait.
The value of signal is the previous (or initial) value of func for the
particular signal.
After a fork or vfork the child inherits all signals. An execve resets
all caught signals to the default action; ignored signals remain
ignored.
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signal(3-ucb) (BSD Compatibility Package) signal(3-ucb)
NOTES
The handler routine can be declared like this:
void handler(sig, code, scp, addr)
int sig, code;
struct sigcontext *scp;
char *addr;
In this example:
sig Signal number.
code Parameter of certain signals that provides additional detail.
scp Pointer to the sigcontext structure (defined in <signal.h>),
used to restore the context from before the signal.
addr Additional address information.
RETURN VALUE
The previous action is returned on a successful call. Otherwise, -1 is
returned and errno is set to indicate the error.
DIAGNOSTICS
signal fails and no action takes place.
EINVAL sig is not a valid signal number, or is SIGKILL or SIGSTOP.
SEE ALSO
kill(1), execve(2), fcntl(2), fork(2), getrlimit(2), kill(2),
ptrace(2), read(2), sigaction(2), wait(2), write(2), sigblock(3),
sigpause(3), sigsetmask(3), sigstack(3), sigvec(3), wait3(3),
getitimer(3C), setjmp(3C), setjmp(3C-ucb), signal(5), termio(7).
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