LXXX. 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).

Process Control support in PHP is not enabled by default. You will need to use the --enable-pcntl configuration option when compiling PHP to enable Process Control support.

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

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.

Table 1. Supported Signals


Process Control Example

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


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