resolver(5)                                                 resolver(5)

  resolver

  NAME

    resolver - resolver configuration file

  SYNOPSIS

    /etc/resolv.conf

  DESCRIPTION

    The resolver routines are a set of routines in the C library 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.

    On a normally configured system, this file should not be necessary. The
    only name server to be queried will be on the local computer, 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 as follows:

    nameserver
        Internet address (in dot notation) of a name server that the resolver
        routines should query. Up to MAXNS (currently three) name servers can
        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 computer. (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
        is made).

    domain
        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(2); the domain part is taken to be everything after the
        first ... Finally, if the host name does not contain a domain part,
        the root domain is assumed.

    search
        Search list for host-name lookup. The search list is normally
        determined from the local domain name; by default, it contains only
        the local domain name. This can 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 might be slow and will generate a lot of network
        traffic if the servers for the listed domains are not local; 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.

    sortlist
        Allows addresses returned by gethostbyname(2) to be sorted. A sortlist
        is specified by Internet Protocol (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 can be specified. For example:
        sortlist 130.155.160.0/255.255.240.0 130.155.0.0

    options
        Allows certain internal resolver variables to be modified. The syntax
        is option... where option is one of the following:

        debug
            Sets RES_DEBUG in _res.options.
        ndots: n
            Sets a threshold for the number of dots that must appear in a name
            given to res_query() 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.

    The domain and search keywords are mutually exclusive. If more than one
    instance of these keywords is present, the last instance takes precedence.

    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 previously in
    Options.

    The keyword and value must appear on a single line, and the keyword (such
    as nameserver) must start the line. The value follows the keyword,
    separated by white space.

  FILES

    /etc/resolve.conf

  SEE ALSO

    gethostbyname(2)

    resolver(3)