on April 30, 2018. Because it is an obsolete product, official ISO downloads are generally no longer available on the Cisco Software Download portal unless you have a legacy service contract. Cisco Community Technical Specifications for Cisco ACS 5.5
: SNS 3415 and 3495, as well as legacy CSACS-1121 appliances. Operating System : Linux-based security-hardened image. Internet Archive Migration to Cisco ISE Cisco recommends all ACS 5.5 users migrate to Cisco Identity Services Engine (ISE) , as ACS is no longer supported. Cisco Community Migration Tool : Cisco provides a specific ACS-to-ISE Migration Tool Cisco Acs 5.5 Iso Download
: For newer versions like ISE 3.1+, you must first migrate to ISE 3.0 before upgrading further, as the direct ACS migration tool is deprecated in newer releases. Cisco Community Upgrade and Patching Cisco Secure Access Control System 5.5 Data Sheet on April 30, 2018