Apache Process Lifespan: When Do mod-php Child Processes Terminate?


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When Apache uses mod_php with the prefork MPM, each HTTP request spawns a separate child process. These processes don't terminate immediately after sending the response - they remain alive according to Apache's configuration parameters.

# Typical Apache prefork configuration
<IfModule prefork.c>
StartServers       5
MinSpareServers    5
MaxSpareServers   10
MaxClients       150
MaxRequestsPerChild  10000
</IfModule>

Several configuration directives determine how long processes stay alive:

  • MaxRequestsPerChild: Maximum requests a process handles before terminating
  • KeepAlive: Whether TCP connection persists for multiple requests
  • KeepAliveTimeout: How long to wait for subsequent requests

Consider this scenario with default settings:

// PHP script that runs for 1 second
<?php
sleep(1);
echo "Done";
?>

The process will:

  1. Start handling the request
  2. Execute the PHP script (1 second)
  3. Send response headers
  4. Stream response body
  5. Remain alive for future requests until MaxRequestsPerChild is reached

Long-running processes can:

  • Consume memory between requests
  • Maintain PHP opcache contents
  • Potentially leak resources if scripts aren't clean

For high-traffic sites, consider these tuning parameters:

# Optimized configuration for busy PHP applications
MaxRequestsPerChild 500
KeepAlive On
KeepAliveTimeout 2

This balances process reuse with memory management, preventing gradual memory leaks while maintaining performance benefits of process reuse.

In a typical Apache prefork MPM setup with mod_php, child processes are created to handle incoming HTTP requests. The lifespan of these processes is governed by several configuration directives and environmental factors.

Apache child processes handling mod_php requests do not terminate immediately after sending the response. The complete sequence is:

  1. PHP finishes executing the script
  2. Apache sends all response data to the client
  3. The process remains alive until the TCP connection is fully closed
  4. The process returns to the Apache process pool for reuse

These Apache directives control process behavior:


# In httpd.conf
MaxRequestsPerChild 10000  # Process dies after serving this many requests
KeepAliveTimeout 5         # Seconds to wait for subsequent requests
Timeout 300                # Maximum time to receive the entire request

Consider this PHP script that demonstrates the behavior:


<?php
// Slow response example
header('Content-Type: text/plain');
echo "Starting response\n";
for ($i = 1; $i <= 5; $i++) {
    echo "Data chunk $i\n";
    ob_flush();
    flush();
    sleep(1);
}
echo "End of response\n";

You can verify process behavior using these Linux commands:


# Monitor Apache processes
watch -n 1 "ps aux | grep 'apache2\|httpd' | grep -v grep"

# Check established connections
netstat -tulpn | grep httpd

Long-running processes impact server resources. Optimize by:

  • Tuning MaxRequestsPerChild based on memory leaks
  • Setting appropriate KeepAliveTimeout
  • Using opcode caching (OPcache) for PHP
  • Implementing process health checks