Section: Linux Programmer's Manual (5)
The resolver is a set of routines in the C library that provide access to the Internet Domain Name System (DNS). The resolver configuration file contains information that is read by the resolver routines the first time they are invoked by a process. The file is designed to be human readable and contains a list of keywords with values that provide various types of resolver information. The configuration file is considered a trusted source of DNS information (e.g., DNSSEC AD-bit information will be returned unmodified from this source).
If this file does not exist, only the name server on the local machine will be queried; the domain name is determined from the hostname and the domain search path is constructed from the domain name.
The different configuration options are:
sortlist 18.104.22.168/255.255.240.0 22.214.171.124
where option is one of the following:
Some programs behave strangely when this option is turned on.
The domain and search keywords are mutually exclusive. If more than one instance of these keywords is present, the last instance wins.
The search keyword of a system's resolv.conf file can be overridden on a per-process basis by setting the environment variable LOCALDOMAIN to a space-separated list of search domains.
The options keyword of a system's resolv.conf file can be amended on a per-process basis by setting the environment variable RES_OPTIONS to a space-separated list of resolver options as explained above under options.
The keyword and value must appear on a single line, and the keyword (e.g., nameserver) must start the line. The value follows the keyword, separated by white space.
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