Which process should be checked when troubleshooting registration issues between Cisco FMC and managed devices to verify that secure communication is occurring?

`fpcollect` is a utility for gathering diagnostic data from the Firepower device, not a process directly involved in establishing the secure communication tunnel itself.

`dhclient` is the DHCP client process, used for obtaining IP addresses, and is not directly involved in the secure management communication tunnel between FMC and FTD.

`sfmgr` (Sensor Manager) is responsible for managing Snort and other security services on the FTD, but it is not the process that establishes or manages the secure communication tunnel to the FMC.

The `sftunnel` process on both the Cisco FMC and the managed FTD device is responsible for establishing and maintaining the secure, encrypted communication tunnel. This tunnel is critical for successful device registration and all subsequent management and event exchange, so checking its status is vital for troubleshooting.