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RESOLVER(5)		       File Formats Manual		     RESOLVER(5)

NAME
     resolver -- resolver configuration file

SYNOPSIS
     resolv.conf

DESCRIPTION
     The  resolver(3) is a set of routines in the C library which provide access
     to the Internet Domain Name System.  The resolver configuration  file  con-
     tains information that is read by the resolver routines the first time they
     are invoked by a process.

     The  file	is  read line by line.	Anything after a `#' or `;' character is
     considered a comment and discarded.  Blank lines are  ignored.   The  first
     word  on  each non-blank line is a keyword which determines how the rest of
     the line is interpreted.  Available keywords are:

     nameserver address
	     IPv4 or IPv6 address of a name  server  that  the	resolver  should
	     query.   Up  to  MAXNS  (currently 3) name servers may be listed on
	     separate lines.  If there are multiple servers,  the  resolver  li-
	     brary queries them in the order listed, unless RES_ROTATE is in ef-
	     fect  (See  the rotate option below).  If no nameserver entries are
	     present, the default is to use the name server  on  the  local  ma-
	     chine.   (The  algorithm  used  is to try a name server, and if the
	     query times out, try the next, until out of name servers, then  re-
	     peat  trying all the name servers until a maximum number of retries
	     are made).

     domain name
	     Set both the local domain name and the search list to  name.   Most
	     queries  for  names within this domain can use short names relative
	     to the local domain.  If no domain name has been set, it is derived
	     from the local host name returned	by  gethostname(3);  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 name1 [name2 ...]
	     Set the domain search list.  Additionally, sets the local domain to
	     name1.   Most  resolver queries will be attempted using each compo-
	     nent 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  do-
	     mains.

	     The search list is currently limited to six domains with a total of
	     256 characters.

     sortlist addr1[/plen1] [addr2[/plen2] ...]
	     Sort  order for query results in the form of a list of addr/mask or
	     addr/plen entries, for instance:

	     sortlist 198.51.100.0/24 203.0.113.0/255.255.255.0 2001:db8::/32

	     Masks are only supported for IPv4.  If the mask or prefix length is
	     omitted, it defaults to historical class-based addressing for  IPv4
	     and to 64 for IPv6.

	     Query  results  that  match one of the sort list entries are sorted
	     accordingly and ahead of query results that don't.  If multiple re-
	     sults match a single sort list entry, the order is unspecified.

	     If multiple sortlist lines are encountered, entries are appended to
	     the list in the order in which they were encountered, up to a maxi-
	     mum of ten.

     options
	     Options allows certain internal resolver variables to be  modified.
	     The following options are supported:

	     debug   Set RES_DEBUG in _res.options.

	     usevc   Set RES_USEVC to use TCP instead of UDP for queries.

	     ndots:n
		     Set a threshold for the number of dots which must appear in
		     a	name  given  to  res_query() (see resolver(3)) 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.

	     timeout:n
		     Set the initial amount of time the resolver will wait for a
		     response from a remote  name  server  before  retrying  the
		     query  via  a different name server.  The resolver may wait
		     longer during subsequent retries of the current query since
		     an exponential back-off is applied to  the  timeout  value.
		     Measured  in  seconds,  the default is RES_TIMEOUT, the al-
		     lowed maximum is RES_MAXRETRANS (see <resolv.h>).

	     attempts:n
		     Set the number of times the resolver will send a  query  to
		     each  of its name servers before giving up and returning an
		     error  to	the  calling  application.    The   default   is
		     RES_DFLRETRY,  the  allowed  maximum  is  RES_MAXRETRY (see
		     <resolv.h>).

	     edns0   Set RES_USE_EDNS0.  Attach an OPT pseudo-RR for  the  EDNS0
		     extension,  as  specified in RFC 2671.  This allows the re-
		     solver to advertise a larger UDP receive buffer size,  per-
		     mitting responses larger than the original 512-byte limit.

	     inet6   Set  RES_USE_INET6.   Causes  the	resolver to look up AAAA
		     records before A records and to  map  IPv4  responses  into
		     IPv6 addresses.  The use of this option is discouraged.

	     insecure1
		     Set  RES_INSECURE1.   This  disables the check that the re-
		     sponse was received from the same server to which the query
		     was sent.	Use of this option is a security risk and is not
		     recommended.

	     insecure2
		     Set RES_INSECURE2.  This disables the check  that	the  re-
		     sponse  contains  a  query  matching the one that was sent.
		     Use of this option is a security risk  and  is  not  recom-
		     mended.

	     no-check-names
		     Set  RES_NOCHECKNAME.   This disables the check of incoming
		     host names for invalid characters such as underscore,  non-
		     ASCII, or control characters.

	     no-debug
		     Clears RES_DEBUG.	See debug above.

	     no-rotate
		     Clears RES_ROTATE.  See rotate below.

	     no-tld-query
		     Set RES_NOTLDQUERY.  This tells the resolver not to attempt
		     to  resolve  a  top level domain name, that is, a name that
		     contains no dots.	Use of this option does not prevent  the
		     resolver  from obeying the standard domain and search rules
		     with the given name.

	     rotate  Set RES_ROTATE.  This causes the  resolver  to  round-robin
		     among  the  configured name servers, distributing the query
		     load instead of always trying the first listed server.

	     reload-period:n
		     The   resolver   checks   the    modification    time    of
		     /etc/resolv.conf  if more than n seconds have elapsed since
		     the last check.  If the file has changed, it  is  automati-
		     cally reloaded.  The default for n is two seconds.  Setting
		     it to zero disables the file check.

	     Options may also be passed as a space- or tab-separated list in the
	     RES_OPTIONS environment variable.	This environment variable is ap-
	     plied after the configuration file has been read.

     The  domain  and  search keywords are mutually exclusive.	If more than one
     instance of these keywords is present, the last instance will override  all
     previous instances.

     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.

ENVIRONMENT
     LOCALDOMAIN
	     If  set,  overrides the local domain and search list set in the re-
	     solver configuration file.

     RES_OPTIONS
	     If set, its value is split into words and interpreted  as	resolver
	     options  as  described for the options keyword in the resolver con-
	     figuration file.

FILES
     /etc/resolv.conf
	     resolver configuration file

EXAMPLES
     # Set the local domain to example.com and the search list to
     # example.com, example.net, example.org
     search example.com example.net example.org

     # Set the local domain and search list to example.com,
     # completely overriding the previous line
     domain example.com

     # Use this if you are running a local caching forwarding (or
     # recursing) resolver like local-unbound(8)
     nameserver 127.0.0.1

     # IP address of the local or ISP name service
     nameserver 198.51.100.53
     nameserver 203.0.113.53

     # Enable EDNS0, which tells the name server that we are capable of
     # handling large responses.  This is required for DNSSEC.
     options edns0

SEE ALSO
     getaddrinfo(3), gethostbyname(3), gethostname(3), resolver(3), hostname(7),
     resolvconf(8)

HISTORY
     The resolv.conf file format appeared in 4.3BSD.

FreeBSD 15.1 STABLE		  July 6, 2026			     RESOLVER(5)
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