Timo Röhling <[email protected]> writes: > Hi, > > * Marc Haber <[email protected]> [2025-10-13 22:22]: >> The biggest question that I still have is why we are writing an >> /etc/hosts with "127.0.1.1 apollo.example.com apollo". Without that, >> the FQDN of the system is incorrect. But why 127.0.1.1? Arch Linux >> does it the same way, but they don't explain why, either. > Even though most people associate 127.0.0.1 with the loopback > interface, the whole 127.0.0.0/8 block is actually reserved for that > purpose, and *any* address in that block loops back to your own host > (just for fun, try "ssh 127.234.56.78" if you have an SSH server > running on your computer). > > 127.0.1.1 is not special, it merely happens to be an address that > a) maps to your own host, and > b) has no other name assigned to it which would conflict in a reverse > lookup (127.0.0.1 is mapped to "localhost"). > > The usual "trick" to get your own domain name is via hostname > canonicalization, i.e, you run gethostbyname("apollo"), which returns > 127.0.1.1, and afterwards gethostbyaddr(127.0.1.1), which returns > "apollo.example.com". The 127.0.1.1 entry in /etc/hosts makes this > work and still lets the software on your computer behave exactly as if > your computer had a static IP with a proper DNS entry, regardless of > your actual network setup. >
I think the missing bit of explanation in this thread is: why would anyone know "apollo" but not "appollo.example.com"? both of these strings are written by the admin in /etc/hosts which is a file that has probably never been changed (and probably doesnt tell you anything much about reaching the system externally) ie - what is the actual problem these settings are trying to solve?
