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LXXXIV. Process Control Functions


Process Control support in PHP implements the Unix style of process creation, program execution, signal handling and process termination. Process Control should not be enabled within a webserver environment and unexpected results may happen if any Process Control functions are used within a webserver environment.

This documentation is intended to explain the general usage of each of the Process Control functions. For detailed information about Unix process control you are encouraged to consult your systems documentation including fork(2), waitpid(2) and signal(2) or a comprehensive reference such as Advanced Programming in the UNIX Environment by W. Richard Stevens (Addison-Wesley).

PCNTL now 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 use the declare() statement to specify the locations in your program where callbacks are allowed to occur. This allows you to minimize the overhead of handling asynchronous events. In the past, compiling PHP with pcntl enabled would always incur this overhead, whether or not your script actually used pcntl.

There is one adjustment that all pcntl scripts prior to PHP 4.3.0 must make for them to work which is to either to use declare() on a section where you wish to allow callbacks or to just enable it across the entire script using the new global syntax of declare().

Note: This extension is not available on Windows platforms.


No external libraries are needed to build this extension.


Process Control support in PHP is not enabled by default. You have to compile the CGI or CLI version of PHP with --enable-pcntl configuration option when compiling PHP to enable Process Control support.

Note: Currently, this module will not function on non-Unix platforms (Windows).

Runtime Configuration

This extension has no configuration directives defined in php.ini.

Resource Types

This extension has no resource types defined.

Predefined Constants

The following list of signals are supported by the Process Control functions. Please see your systems signal(7) man page for details of the default behavior of these signals.

WNOHANG (integer)

WUNTRACED (integer)

SIG_IGN (integer)

SIG_DFL (integer)

SIG_ERR (integer)

SIGHUP (integer)

SIGINT (integer)

SIGQUIT (integer)

SIGILL (integer)

SIGTRAP (integer)

SIGABRT (integer)

SIGIOT (integer)

SIGBUS (integer)

SIGFPE (integer)

SIGKILL (integer)

SIGUSR1 (integer)

SIGSEGV (integer)

SIGUSR2 (integer)

SIGPIPE (integer)

SIGALRM (integer)

SIGTERM (integer)

SIGSTKFLT (integer)

SIGCLD (integer)

SIGCHLD (integer)

SIGCONT (integer)

SIGSTOP (integer)

SIGTSTP (integer)

SIGTTIN (integer)

SIGTTOU (integer)

SIGURG (integer)

SIGXCPU (integer)

SIGXFSZ (integer)

SIGVTALRM (integer)

SIGPROF (integer)

SIGWINCH (integer)

SIGPOLL (integer)

SIGIO (integer)

SIGPWR (integer)

SIGSYS (integer)

SIGBABY (integer)


This example forks off a daemon process with a signal handler.

Example 1. Process Control Example


$pid = pcntl_fork();
if ($pid == -1) {
     die("could not fork"); 
} else if ($pid) {
     exit(); // we are the parent 
} else {
     // we are the child

// detatch from the controlling terminal
if (!posix_setsid()) {
    die("could not detach from terminal");

// setup signal handlers
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");

// loop forever performing tasks
while(1) {

    // do something interesting here


function sig_handler($signo) {

     switch($signo) {
         case SIGTERM:
             // handle shutdown tasks
         case SIGHUP:
             // handle restart tasks
             // handle all other signals



See Also

A look at the section about POSIX functions may be useful.

Table of Contents
pcntl_exec --  Executes specified program in current process space
pcntl_fork -- Forks the currently running process
pcntl_signal -- Installs a signal handler
pcntl_waitpid -- Waits on or returns the status of a forked child
pcntl_wexitstatus --  Returns the return code of a terminated child
pcntl_wifexited --  Returns TRUE if status code represents a successful exit
pcntl_wifsignaled --  Returns TRUE if status code represents a termination due to a signal
pcntl_wifstopped --  Returns TRUE if child process is currently stopped
pcntl_wstopsig --  Returns the signal which caused the child to stop
pcntl_wtermsig --  Returns the signal which caused the child to terminate
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