Updated: 28 September 2026 · Applies to: CloudLinux OS with cPanel & WHM
On servers with LiteSpeed and ConfigServer Firewall (CSF), PHP sites can return "503 Service Unavailable" even though the account is not at its resource limits. A common cause is LFD (CSF's login failure daemon) killing LiteSpeed PHP processes that it thinks are suspicious.
Check
grep -i kill /var/log/lfd.log | tail
Fix
Tell LFD to ignore LiteSpeed's processes by adding them to /etc/csf/csf.pignore, for example:
exe:/usr/local/bin/lsphp exe:/usr/local/lsws/bin/lshttpd
Check the exact executable paths on your server with ps aux | grep -E "lsphp|lshttpd" (the lshttpd path can include a version number), then restart LFD: systemctl restart lfd.
