RESOLV.CONF(5) | File Formats Manual | RESOLV.CONF(5) |
resolv.conf
—
resolv.conf
file specifies how the
resolver(3) routines in the C
library (which provide access to the Internet Domain Name System) should
operate. 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.
On a normally configured system this file should not be necessary. The only name server to be queried will be on the local machine, the domain name is determined from the host name, and the domain search path is constructed from the domain name.
The different configuration options are:
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).The search list is currently limited to six domains with a total of 1024 characters.
sortlist 130.155.160.0/255.255.240.0 130.155.0.0
options option ...
where option is one of the following:
RES_TIMEOUT
(see
⟨resolv.h⟩).RES_DFLRETRY
(see
⟨resolv.h⟩).RES_ROTATE
in
_res.options, which causes round robin selection
of nameservers from among those listed. This has the effect of
spreading the query load among all listed servers, rather than having
all clients try the first listed server first every time.RES_NOCHECKNAME
in
_res.options, which disables the modern BIND
checking of incoming host names and mail names for invalid characters
such as underscore (‘_’), non-ASCII, or control
characters. This is the default.RES_NOCHECKNAME
in
_res.options, which enables the modern BIND
checking of incoming host names and mail names as described
above.RES_NOTLDQUERY
in
_res.options. This option causes
res_nsearch
() to not attempt to resolve a
unqualified name as if it were a top level domain (TLD). This option
can cause problems if the site has “localhost” as a TLD
rather than having localhost on one or more elements of the search
list. This option has no effect if neither
RES_DEFNAMES
or
RES_DNSRCH
is set.The domain and search keywords are mutually exclusive. If more than one instance of these keywords is present, the last instance will override.
The search keyword of a system's
resolv.conf file can be overridden on a per-process
basis by setting the environment variable
LOCALDOMAIN
to a space-separated list of search
domains.
The options keyword of a system's
resolv.conf file can be amended on a per-process
basis by setting the environment variable
RES_OPTIONS
to a space-separated list of resolver
options as explained above.
The keyword and value must appear on a single line, and the keyword (e.g. nameserver) must start the line. The value follows the keyword, separated by white space.
resolv.conf
resides in
/etc.Paul Vixie, Kevin J. Dunlap, and Michael J. Karels, Name Server Operations Guide for BIND, CSRG,, Department of Electrical Engineering and Computer Sciences,, University of California, Berkeley, Release 4.9.4, http://www.dns.net/dnsrd/docs/bog/bog.html, July 16, 1996.
resolv.conf
file format appeared in
4.3BSD.
September 9, 2012 | NetBSD 9.4 |