Q. How do I identify Linux server ECC memory modules from a shell prompt?

A. You need to count the chips on the module. If memory module has 9 chips per sides, it is ECC memory (EDAC protected memory). It may or may not be registered. If the memory module has 8 chips per side, it is not ECC memory modules.

You can get this information by visiting your BIOS setup menu. Another option is to use dmidecode command to dump bios memory information from a shell prompt:
# dmidecode --type memory