resolv.conf - resolver configuration file
The resolver is a set of routines that provide access to the
Internet Domain Name System. See resolver(3RESOLV).
resolv.conf is a configuration file that contains the infor-
mation 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 resolv.conf file contains the following configuration
Specifies the Internet address in dot-notation format
of a name server that the resolver is to query. Up to
MAXNS name servers may be listed, one per keyword. See
<resolv.h>. If there are multiple servers, the
resolver library queries them in the order listed. If
no name server entries are present, the resolver
library queries the name server on the local machine.
The resolver library follows the algorithm to try a
name server until the query times out. It then tries
the the name servers that follow, until each query
times out. It repeats all the name servers until a
maximum number of retries are made.
Specifies the 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 sysinfo(2) or from
gethostname(3C). (Everything after the first `.' is
presumed to be the domain name.) If the host name does
not contain a domain part, the root domain is assumed.
You can use the LOCALDOMAIN environment variable to
override the domain name.
The 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. You
can change the default behavior 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. This
process may 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
and a total of 256 characters.
Allows addresses returned by the libresolv-internal
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 220.127.116.11/255.255.240.0 18.104.22.168
Allows certain internal resolver variables to be modi-
fied. The syntax is
options option ...
where option is one of the following:
debug Sets RES_DEBUG in the _res.options field.
Sets a threshold floor for the number of dots
which must appear in a name given to res_query()
before an initial absolute (as-is) query is per-
formed. See resolver(3RESOLV). The default value
for n is 1, which means that if there are any
dots in a name, the name is tried first as an
absolute name before any search list elements
are appended to it.
Sets the amount of time the resolver will wait
for a response from a remote name server before
retrying the query by means of a different name
server. Measured in seconds, the default is
RES_TIMEOUT. See <resolv.h>. The timeout and
retrans values are the starting point for an
exponential back off procedure where the timeout
is doubled for every retransmit attempt.
Sets the number of times the resolver will send
a query to its name servers before giving up and
returning an error to the calling application.
The default is RES_DFLRETRY. See <resolv.h>.
Sets RES_ROTATE in _res.options. The name
servers are queried round-robin from among those
listed. The query load is spread among all
listed servers, rather than having all clients
try the first listed server first every time.
Sets RES_NOCHECKNAME in _res.options. This dis-
ables the modern BIND checking of incoming host
names and mail names for invalid characters such
as underscore (_), non-ASCII, or control charac-
inet6 Sets RES_USE_INET6 in _res.options. In the
Solaris BIND port, this has no effect on
gethostbyname(3NSL). To retrieve IPv6 addresses
or IPv4 addresses in mapped form, use
getipnodebyname(3SOCKET) instead of setting
The domain and search keywords are mutually exclusive. If
more than one instance of these keywords is present, the
last instance takes precedence.
You can override the search keyword of the system
resolv.conf file on a per-process basis by setting the
environment variable LOCALDOMAIN to a space-separated list
of search domains.
You can amend the options keyword of the system resolv.conf
file on a per-process basis by setting the environment vari-
able RES_OPTIONS to a space-separated list of resolver
The keyword and value must appear on a single line. Start
the line with the keyword, for example, nameserver, followed
by the value, separated by white space.
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Interface Stability | Standard BIND 8.2.4 |
domainname(1M), in.named(1M), sysinfo(2),
gethostname(3C), resolver(3RESOLV), attributes(5)
Vixie, Paul, Dunlap, Keven J., Karels, Michael J. Name
Server Operations Guide for BIND. Internet Software Consor-
Man(1) output converted with