The file /etc/resolv.conf is the configuration file for the DNS resolver, which translates domain names to IP addresses by querying the DNS servers. The file supports several keywords that provide various types of resolver information. Two of the keywords that can be used in /etc/resolv.conf are:
nameserver: This keyword specifies the IP address of the DNS server that the resolver can query against. Up to three nameservers can be configured, and the resolver will try them in order until one responds or all fail.
search: This keyword specifies a list of search domains that the resolver will append to the domain name when performing a query. For example, if the search list is example.com example.net, and the resolver queries for host, it will try host.example.com and host.example.net in order. The search list can have up to six domains, with a maximum of 256 characters in total.
The other keywords in the question are not valid for /etc/resolv.conf. The file does not support any keywords for substitution, lookup, or method. However, there are other keywords that can be used, such as:
domain: This keyword specifies the local domain name of the system. It is mutually exclusive with the search keyword, and only one instance of either can be used.
options: This keyword specifies various options that modify the behavior of the resolver. For example, the option rotate can be used to rotate the nameservers in a round-robin fashion, instead of trying them in order. Multiple options can be specified, separated by spaces.
References:
3: The /etc/resolv.conf File | Baeldung on Linux
1: /etc/resolv.conf - QNX
4: Chapter 33. Manually configuring the /etc/resolv.conf file
