how to add nameserver in resolv.conf

I researched about how to add a name server in the file resolv.conf, I found this command on this site:

namerslv -a -i ip address

I'm also confused with the example in that site, this one:

namerslv -a { -i IPAddress | -D DomainName| -S SearchList}

so which one I should use if I want to add just the name server?

-i
-D or
-S (I have doubts about this)

When I try to use it, it's not supported on my Linux.

Also, why is it important to list at least two name servers in the file resolv.conf?

Solution

vim /etc/resolv.conf

Edit file - usually you would have:

nameserver 8.8.8.8
nameserver 8.8.4.4

possibly:

domain local.example.com

or:

search local.example.com

This will help you with searches like:

host hostname

rather then

host fqdn

Adding more than one DNS entry is important from the redundancy point of view - if one fails you can still resolve names.