resolver configuration file
The ``resolver'' is a set of routines in the socket library (see
that provide access to the Internet Domain Name Service.
The resolver configuration file, /etc/resolv.conf,
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 different configuration keywords are:
The domain and search keywords are
mutually exclusive for host-name lookup.
If more than one of these
keywords is present, the last instance will override.
Local domain name.
Most queries for names within this domain can use short names
relative to the local domain.
If no domain entries are present, the domain is determined from
the local host name returned by
the domain is
taken to be everything after the first ``.''.
if the host name does not contain a domain part, the root
domain is assumed.
Internet address (in dot notation) of a
name server that the resolver should query.
Up to three name servers may be
listed; in that case 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).
Allows certain internal resolver variables to be modified.
The syntax is:
options option ...
where option is one of the following:
Sets RES_DEBUG in
Sets a threshold for the number of dots which must appear
in a name given to res_query (see
before an initial absolute query will be made.
The default for n is ``1'', meaning that if there
are any dots in a name, the name will be tried first as an
absolute name before any search list elements are
appended to it.
Search list for host-name lookup. The search list is
normally determined from the local domain name; by default,
it begins with the local domain name, then successive
parent domains that have at least two components in their
names. For example:
search subnet1.company.com company.com
This default order may be changed by listing the desired domain
search path following the search keyword with
spaces or tabs separating the names. 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 search list is currently limited to six domains
with a total of 256 characters.
Allows addresses returned by
gethostbyname to be sorted. A sortlist is
specified by IP address netmask pairs. The
netmask is optional and defaults to the natural netmask of
the net. The IP address and optional network
pairs are separated by slashes. Up to 10 pairs may be
specified, for example:
sortlist 188.8.131.52/255.255.240.0 184.108.40.206
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 under the options keyword description.
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.
Lines beginning with a ``;'' or ``#'' are treated as
comments and ignored.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004