resolver(4)

Internet (IP) address, in dot notation, of a name server that the resolver should query. Up to MAXNS (currently 3) 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 machine. (The algorithm used is: Try a name server; if the query times out, try the next and continue until all name servers have been tried, then repeat trying all the name servers until a maximum number of retries have been 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() (see gethostname(2)); the domain part is interpreted as everything after the first dot (.). Finally, if the host name does not contain a domain part, the root domain is assumed.

Retransmission timeout. It is interpreted during the res_init() (see resolver(3N)) call. It has higher precedence than setting it through the set_resfeild() (see resolver(3N)) API and lower precedence than setting it through the RES_RETRANS (see resolver(3N)) environment variable. Whenever an invalid value is specified for retrans, a message is flagged in syslog. The default value is 5000 milliseconds.

To use the retrans option, add the following name-value pair in /etc/resolv.conf:

Example: To set the retransmission value to 6000, use:

Number of retries. This is interpreted during the res_init() (see resolver(3N)) call. It has higher precedence than setting it through the set_resfeild() (see resolver(3N)) API and lower precedence than setting it through the RES_RETRY (see resolver(3N)) environment variable. Whenever an invalid value is specified for retry, a message is flagged in syslog. The default value is 4.

To use the retry option, add the following name-value pair in /etc/resolv.conf:

Example: To set the number of retries to 6, use:

Search list for host-name lookup. If the search option is not used the search list will contain only the local domain name. The search list 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 may be slow and generates a lot of network traffic if the servers for the listed domains are not local, and that queries 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.

The first domain in the search list must be the local domain for short names to work properly in various files (such as .rhosts and inetd.sec)

Causes addresses returned by gethostbyname(3N) to be sorted in accordance with network numbers specified in the address list. This option allows you to specify which subnets and networks for gethostbyname() to prefer if it receives multiple addresses as the result of a query from the domain nameserver. The syntax is

A sortlist is specified by IP address netmask pairs. The netmask is optional and defaults to the netmask of the net. The IP address and optional netmask pairs are separated by slashes. Up to 10 pairs may be specified. The pairs are separated by blank spaces.

The following sortlist directive sorts the address on 128.32.42 subnet,

The argument after the slash is the subnet mask for the subnet in question. To prefer an entire network, you can omit the slash and the subnet mask:

gethostbyname() sorts any addresses in a reply that match these arguments into the order in which they appear in the sortlist, and appends those addresses that do not match to the end.

Options allows certain internal resolver variables to be modified. The syntax is

where currently the option supported is the following:

Resolver configuration file.