- Method 1: \['SERVER_ADDR'] from Apache/Nginx (most reliable)
- Method 2: /sbin/ip (absolute path, works if ip not in PATH)
- Method 3: Parse /proc/net/route for default gateway interface + IP
- Method 4: hostname -I (space-separated IPs)
- Method 5: ifconfig (fallback for older systems)
- Method 6: Socket connection to 8.8.8.8 (pure PHP, no shell commands)
Each method validates IP and skips loopback (127.x, ::1, ::ffff:127.x)
Fixes 'Unavailable' when shell commands fail or aren't available