| SIGNAL(3) | Library Functions Manual | SIGNAL(3) | 
signal —
#include <signal.h>
void (*
  
  signal(int
    sig, void
    (*func)(int)))(int);
signal() facility is a simplified interface to the
  more general sigaction(2)
  facility.
Signals allow the manipulation of a process from outside its
    domain as well as allowing the process to manipulate itself or copies of
    itself (children). There are two general types of signals: those that cause
    termination of a process and those that do not. Signals which cause
    termination of a program might result from an irrecoverable error or might
    be the result of a user at a terminal typing the `interrupt' character.
    Signals are used when a process is stopped because it wishes to access its
    control terminal while in the background (see
    tty(4)). 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 result in the termination of the process receiving them 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 otherwise.
    Except for the SIGKILL and
    SIGSTOP signals, the
    signal() function allows for a signal to be caught,
    to be ignored, or to generate an interrupt. See
    signal(7) for comprehensive
    list of supported signals.
The func procedure allows a user to choose
    the action upon receipt of a signal. To set the default action of the signal
    to occur as listed above, func should be
    SIG_DFL. A SIG_DFL resets
    the default action. To ignore the signal func should
    be SIG_IGN. This will cause subsequent instances of
    the signal to be ignored and pending instances to be discarded. If
    SIG_IGN is not used, further occurrences of the
    signal are automatically blocked and func is
  called.
The handled signal is unblocked when the function returns and the process continues from where it left off when the signal occurred.
func() remains installed after a signal has been
  delivered.For some system calls, if a signal is caught while the call is
    executing and the call is prematurely terminated, the call is automatically
    restarted. (The handler is installed using the
    SA_RESTART flag with
    sigaction(2)). The affected
    system calls include read(2),
    write(2),
    sendto(2),
    recvfrom(2),
    sendmsg(2) and
    recvmsg(2) on a
    communications channel or a low speed device and during a
    ioctl(2) or
    wait(2). However, calls that
    have already committed are not restarted, but instead return a partial
    success (for example, a short read count).
When a process which has installed signal handlers forks, the child process inherits the signals. All caught signals may be reset to their default action by a call to the execve(2) function; ignored signals remain ignored.
Only functions that are async-signal-safe can safely be used in signal handlers, see sigaction(2) for a complete list.
SIG_ERR is returned and the global variable
  errno is set to indicate the error.
signal() will fail and no action will take place if one
  of the following occur:
EINVAL]SIGKILL or SIGSTOP.signal() facility appeared in
  4.0BSD.
| June 5, 2016 | NetBSD 9.4 |