nginx. What does the server_name _; entry mean?

Question

linux

I can not get the meaning of such an entry from the documentation. If it's not difficult, please tell me. Thank you.

Answer 1

these characters are not allowed in a domain name, so they are used as the default name for all domains that nginx will process
in other words, if you write any string there that cannot be a domain name, then it will be equivalent to _
for example %, $, ^, &, §, !!??##@@ or any other that does not comply with rfc1034

Answer 2

ac default