# pcntl_signal

(PHP 4 >= 4.0.7, PHP 5)

pcntl_signal — Installs a signal handler

### Description

bool pcntl_signal ( int `$signo` , callback `$handler` [, bool `$restart_syscalls` ] )

The pcntl_signal() function installs a new signal handler for the signal indicated by `signo` .

### Parameters

`signo`

  The signal number.

`handler`

  The signal handler which may be the name of a user created function, or method, or either of the two global constants `SIG_IGN` or `SIG_DFL`.

  > Note: Note that when you set a handler to an object method, that object's reference count is increased which makes it persist until you either change the handler to something else, or your script ends.

`restart_syscalls`

  Specifies whether system call restarting should be used when this signal arrives and defaults to `TRUE`.

### Return Values

Returns `TRUE` on success or `FALSE` on failure.

### ChangeLog

Version | Description
--- | ---
4.3.0 | The `restart_syscalls` parameter was added.
4.3.0 | The ability to use an object method as a callback became available.
4.3.0 | As of PHP 4.3.0 PCNTL uses ticks as the signal handle callback mechanism, which is much faster than the previous mechanism. This change follows the same semantics as using "user ticks". You must use the declare() statement to specify the locations in your program where callbacks are allowed to occur for the signal handler to function properly (as used in the above example).

### Examples

Example#1 pcntl_signal() example

`<?php
// tick use required as of PHP 4.3.0
declare(ticks = 1);
// signal handler function
function sig_handler($signo)
{
switch ($signo) {
case SIGTERM:
// handle shutdown tasks
exit;
break;
case SIGHUP:
// handle restart tasks
break;
case SIGUSR1:
echo "Caught SIGUSR1...\n";
break;
default:
// handle all other signals
}
}
echo "Installing signal handler...\n";
// setup signal handlers
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");
pcntl_signal(SIGUSR1, "sig_handler");
// or use an object, available as of PHP 4.3.0
// pcntl_signal(SIGUSR1, array($obj, "do_something");
echo"Generating signal SIGTERM to self...\n";
// send SIGUSR1 to current process id
posix_kill(posix_getpid(), SIGUSR1);
echo "Done\n"
?>`

### See Also

- pcntl_fork()
- pcntl_waitpid()