domain 聲明主機的域名。很多程序用到它，如郵件系統；當為沒有域名的主機進行DNS 查詢時，也要用到。如果沒有域名，主機名將被使用，刪除所有在第一個點( . )前面的內容。search 它的多個參數指明域名查詢順序。當要查詢沒有域名的主機，主機將在由search 聲明的域中分別查找。domain 和search 不能共存；如果同時存在，后面出現的將會被使用。
下面的說明更清晰
在/etc/resolv.conf 配置文件：domain 和search作用是一樣的
domain linpro.no
search linpro.no uio.no ifi.uio.no
domain function:
Had I typed telnet math.uio.no. with the trailing dot, the resolver would have known it was an FQDN and would have looked up math.uio.no at once, without trying to append the specified domain first. Not all applications are tolerant of the trailing dot, though, so it can't always be specified.
search function:
When ssh gram is executed, the resolver first looks for gram.linpro.no, which does not exist; thengram.uio.no, which does not exist, either; and finally gram.ifi.uio.no, which will succeed because it does exist
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