in document 'Cisco ASA 5500 Series Configuration Guide using the CLI' it mentioned, If a unit boots and detects a peer already running as active, it becomes the standby unit.
My situation is FW1 is set as primary, FW2 is set as secondary. When FW1 is fail, then FW2 take the role as active. When FW1 is ok, it would not take over the role as active, FW2 remain as active.
How can i make the FW1 become active when it is back online? (not by manually turn off FW2 and turn on again)
Preempt is not available on Active/Standby setup. Only for multi context using failover groups.