resolv.conf(4) Kernel Interfaces Manual resolv.conf(4)
NAME
resolv.conf - Resolver configuration file
SYNOPSIS
/etc/resolv.conf
DESCRIPTION
The resolver is a set of routines in the C library (resolver(4)) that provide access to the Internet Domain Name System. The resolver con-
figuration 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 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. For example: keyword value
The file format is as follows: nameserver Address
Internet address (in dot notation) 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). domain
DomainName
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 host name returned by gethostname(); the domain part is taken to be everything after the
first . (dot). Finally, if the host name does not contain a domain part, the root domain is assumed. search Domain_Name1 DomainName2 ...
Search list for host-name lookup. Up to six domains (separated by spaces or tabs) with a total of 256 characters can be specified. If no
search entry is present, the search list consists of the local domain name.
Most resolver queries will be attempted using each component of the search path in turn until a match is found. Note that this process may
be slow and will 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.
You can also specify a search list on a per-process basis by specifying the LOCALDOMAIN environment variable. See resolver(4).
The domain and search keywords are mutually exclusive. If more than one instance of these keywords is present, the last instance will
override. options allow_special all | { char }
Option for defining valid characters in hostnames. Specify all to disable hostname checking (allow all characters) or define a set of
valid characters by using the { char } syntax, where char is the character you want to allow. For example, you can allow the semicolon,
underscore, and colon characters by using { ; \_ : }.
Disabling hostname checking altogether is not recommended. By default, the allow_special option is not set and strict hostname checking is
enforced. options ndots:n
Option for hostname lookup. The n specifies the minimum number of dots a name must contain in order for resolver to look up the name as
given. If the lookup fails, the search list (if specified) is applied. The range for n is from 0 to 15. If no options entry is present,
the minimum number of dots is 1.
You can also specify the number of dots on a per-process basis by using the RES_OPTIONS environment variable. See resolver(4).
CAUTIONS
Any white space entered after the domain name is not ignored but is interpreted as part of the domain name.
RELATED INFORMATION
Commands: named(8)
Functions: gethostbyname(3), resolver(4)
Files: hostname(5) delim off
resolv.conf(4)