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resolver(4) Kernel Interfaces Manual resolver(4) NAME resolver - Internet name domain client DESCRIPTION The resolver is a set of routines in the C library that provide access to the Internet Domain Name System. The resolver configuration file (resolv.conf) contains information that is read by the resolver rou- tines the first time they are invoked by a process. The file is de- signed to be read by humans and contains a list of keywords with values that provide various types of resolver information. The different configuration options are: Internet address (in dot nota- tion) of a name server that the resolver should query. Up to MAXNS (currently 3) name servers may be listed, one per keyword. If there are multiple servers, the resolver library queries them in the order listed. If no nameserver entries are present, the default is to use the name server on the local machine. (The algorithm used is to try a name server, and if the query times out, try the next, until out of name servers, then repeat trying all the name servers until a maximum number of retries are made). Local domain name. Most queries for names within this domain can use short names relative to the local domain. If no domain entry is present, the domain is determined from the local hostname returned by gethostname(); the domain part is taken to be everything after the first dot (.). Finally, if the hostname does not contain a domain part, the root domain is assumed. Search list for hostname lookup. By default, the search list consists of the local do- main name. You can change this system wide by specifying search key- word followed by a list of domain names separated by spaces or tabs, or on a per-process basis by specifying the LOCALDOMAIN environment vari- able followed by a list of domain names separated by spaces or tabs. Most resolver queries will be attempted using each component of the search path in turn until a match is found. This process might be slow and generate a lot of network traffic, if the servers for the listed domains are not local, and that queries will time out if no server is available for one of the domains. The search list is currently limited to six domains with a total of 256 characters. Option for hostname lookup. By default, when a hostname contains one or more dots (.), resolver looks up the name as given before applying the search list. You can change this system wide by specifying options keyword followed by ndots:n, or on a per-process basis by specifying the RES_OP- TIONS environment variable followed by ndots:n. The n specifies the minimum number of dots a name must contain in order to be looked up as given before applying the search list. The range is from 0 to 15. The domain and search keywords are mutually exclusive. If more than one instance of these keywords is present, the last instance will over- ride. The keyword and value must appear on a single line, and the keyword (for example, nameserver) must start the line. The value follows the keyword, separated by white space. FILES /etc/resolv.conf RELATED INFORMATION Functions: gethostbyname(3), res_mkquery(3), res_send(3), res_init(3), dn_comp(3), dn_expand(3) Files: hostname(5) Commands: named(8) delim off resolver(4)