resolv.conf(4)resolv.conf(4)NAMEresolv.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 rou‐
tines the first time they are invoked by a process. The file is
designed to be human readable and contains a list of keywords with val‐
ues 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 spa‐
ces 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 over‐
ride. options allow_special all | { \char }
Option for defining valid characters in hostnames. Specify all to dis‐
able 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, under‐
score, 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 mini‐
mum 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.
SEE ALSO
Commands: named(8)
Functions: gethostbyname(3), resolver(4)
Files: hostname(5)resolv.conf(4)
