resolver(4)resolver(4)NAMEresolver - resolver configuration file
SYNOPSIS
/etc/resolv.conf
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
designed to be read by humans and contains a list of keywords with val‐
ues 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 host
name returned by gethostname(); the domain part is taken to be every‐
thing after the first dot (.). Finally, if the host name does not con‐
tain a domain part, the root domain is assumed. Search list for host
name lookup. By default, the search list consists of the local domain
name. You can change this system wide by specifying search keyword
followed by a list of domain names separated by spaces or tabs, or on a
per-process basis by specifying the LOCALDOMAIN environment variable
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. Enables the sorting of addresses returned by
gethostname. A sortlist comprises pairs of IP addresses and
optional netmasks; each IP address and optional netmask are sep‐
arated by a slash character (/). The netmask is optional, and
defaults to the current network netmask. You can specify up to
10 pairs. For example:
sortlist 130.155.160.0/255.255.240.0 130.155.0.0 Option for host
name lookup. By default, when a host name contains one or more
dots (.), resolver looks up the name as given before applying
the search list. 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.
You can change the resolver options system wide by specifying
options keyword followed a list of resolver options separated by
spaces, or on a per-process basis by specifying the RES_OPTIONS
environment variable followed by a list of resolver options sep‐
arated by spaces.
The domain and search keywords are mutually exclusive. If more than one
instance of these keywords is present, the last instance will override.
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
SEE ALSO
Functions: dn_comp(3), dn_expand(3), gethostbyname(3), res_init(3),
res_mkquery(3), res_query(3), res_search(3), res_send(3)
Files: hostname(5)
Commands: named(8)resolver(4)