resolv.conf - Resolver configuration file
/etc/resolv.conf
The resolver is a set of routines in the C library
(resolver(4)) that provide access to the Internet Domain
Name System. 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 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).
Any white space entered after the domain name is not
ignored but is interpreted as part of the domain name.
Commands: named(8)
Functions: gethostbyname(3), resolver(4)
Files: hostname(5)
resolv.conf(4)
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