When a PHP process terminates with exit code 255, it typically indicates an "out of range" error status. In Unix-like systems, exit codes are 8-bit values (0-255), where 255 often represents an undefined or unhandled failure condition. Here's what might be happening in your case:

// Example script that might cause exit 255

Based on my experience debugging PHP 5.x installations, these are the most frequent causes:

• Missing PHP extensions (compiled-in dependencies not present)
• Segmentation faults in custom PHP extensions
• Resource limitations (memory, file descriptors)
• Signal interruptions (SIGKILL, SIGTERM)

Here's how I would approach diagnosing the issue:

# Step 1: Check PHP error logs
tail -f /var/log/php_errors.log

# Step 2: Run with maximum error reporting
php -d error_reporting=E_ALL -d display_errors=1 script.php

# Step 3: Use strace for system call tracing
strace -f -o trace.log php script.php

Let's simulate the scenario where a required extension is missing:

If scripts run on other machines but fail with 255 on your compiled PHP, consider:

# Compare PHP configurations
php -i > configuration.txt
diff server1_configuration.txt server2_configuration.txt

# Check compiled modules
php -m | sort > modules.txt

For scripts that need to handle this gracefully:

---

When working with custom PHP builds (especially legacy versions like 5.2.9), encountering exit status 255 can be particularly frustrating because:

• It provides no explicit error message
• The script terminates silently mid-execution
• The status code falls in the "reserved" range

In Unix-like systems, exit codes are 8-bit values (0-255). While 0 indicates success, 255 typically means:

#define EXIT_FAILURE 1   /* Failing exit status.  */
#define EXIT_SUCCESS 0   /* Successful exit status.  */

However, when a program tries to return -1, the system converts it to 255 due to modulo-256 arithmetic.

From practical experience, these scenarios frequently trigger status 255:

1. Segmentation Fault in Custom Build

A poorly compiled PHP binary might crash when executing certain operations. Try running with valgrind:

valgrind php your_script.php

2. Missing Extension Dependencies

Example of checking loaded modules:

<?php
print_r(get_loaded_extensions());
?>

3. Resource Limitations

Test with these settings in your script:

<?php
ini_set('memory_limit', '512M');
set_time_limit(0);
// Your problematic code here
?>

Follow this systematic approach:

Step 1: Isolate the Problem

Create a minimal test case:

<?php
// test_segfault.php
$chunk = str_repeat('a', 1024*1024); // 1MB string
// Add suspected functions one by one
?>

Step 2: Check System Logs

On Linux:

grep php /var/log/syslog
dmesg | grep php

Step 3: Compare Environments

Run phpinfo() on working and failing systems:

<?php
phpinfo(INFO_MODULES);
?>

Using GDB for Core Dumps

gdb --args php your_script.php
(gdb) run
(gdb) bt full

Strace Analysis

strace -f -o trace.log php your_script.php

For custom PHP builds:

• Always compile with debug symbols (-g)
• Verify all required libraries: ldd $(which php)
• Consider using Docker for environment consistency