Described is a headless server appliance configured with a secondary actuation mechanism that when actuated, enters the headless server appliance into a diagnostic mode. For example, the diagnostic mode may correspond to a secondary operating system booted from a BIOS component activated by the secondary actuation mechanism. In the diagnostic mode, primitives may be communicated between a client device coupled (e.g., via a network or USB connection) to the headless server appliance, such as to provide the client device with access to the headless server appliance's hard disk. Other primitives, such as communicated via APIs, may provide the client device with access to the BIOS. The secondary operating system and/or client device may perform diagnostics and recovery operations on the headless server appliance. For example, the client device or similar source may restore or update the primary operating system image to a storage medium of the headless server appliance.