resolv.conf(4) File Formats resolv.conf(4)NAMEresolv.conf - resolver configuration file
SYNOPSIS
/etc/resolv.conf
DESCRIPTION
The resolver is a set of routines that provide access to the Internet
Domain Name System. See resolver(3RESOLV). resolv.conf is a configura‐
tion file that contains the 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 val‐
ues that provide various types of resolver information.
The resolv.conf file contains the following configuration directives:
nameserver
Specifies the IPv4 or IPv6 Internet address 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 algo‐
rithm to try a name server until the query times out. It then tries
the name servers that follow, until each query times out. It
repeats all the name servers until a maximum number of retries are
made.
domain
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 pre‐
sumed to be the domain name.) If the host name does not contain a
domain part, the root domain is assumed. You can use the LOCALDO‐
MAIN environment variable to override the domain name.
search
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 list‐
ing 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.
sortlistaddresslist
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 130.155.160.0/255.255.240.0 130.155.0.0
options
Allows certain internal resolver variables to be modified. The syn‐
tax is
options option ...
where option is one of the following:
debug
Sets RES_DEBUG in the _res.options field.
ndots:n
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 performed. 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.
timeout:n
retrans:n
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.
attempts:n
retry:n
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>.
rotate
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.
no-check-names
Sets RES_NOCHECKNAME in _res.options. This disables the modern
BIND checking of incoming host names and mail names for invalid
characters such as underscore (_), non-ASCII, or control char‐
acters.
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, use getaddrinfo(3SOCKET) instead
of setting inet6.
The domain and search keywords are mutually exclusive. If more than one
instance of these keywords is present, the last instance takes prece‐
dence.
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 variable RES_OPTIONS to a
space-separated list of resolver options.
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.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Committed │
├─────────────────────────────┼─────────────────────────────┤
│Standard │BIND 8.3.3 │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOdomainname(1M), sysinfo(2), gethostbyname(3NSL), getnameinfo(3SOCKET),
getipnodebyname(3SOCKET), gethostname(3C), resolver(3RESOLV),
attributes(5)
Vixie, Paul, Dunlap, Keven J., Karels, Michael J. Name Server Opera‐
tions Guide for BIND. Internet Software Consortium, 1996.
SunOS 5.11 15 Dec 2004 resolv.conf(4)
