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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" .\"
.\" @(#)resolver.5 8.1 (Berkeley) 6/5/93 .\" @(#)resolver.5 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$ .\" $FreeBSD$
.\" .\"
.Dd November 7, 2022 .Dd November 19, 2022
.Dt RESOLVER 5 .Dt RESOLVER 5
.Os .Os
.Sh NAME .Sh NAME
.Nm resolver .Nm resolver
.Nd resolver configuration file .Nd resolver configuration file
.Sh SYNOPSIS .Sh SYNOPSIS
.Nm resolv.conf .Nm resolv.conf
.Sh DESCRIPTION .Sh DESCRIPTION
The The
.Xr resolver 3 .Xr resolver 3
is a set of routines in the C library is a set of routines in the C library
which provide access to the Internet Domain Name System. which provide access to the Internet Domain Name System.
The resolver configuration file contains information that is read The resolver configuration file contains information that is read
by the resolver routines the first time they are invoked by a process. 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 The file is designed to be human readable and contains a list of
keywords with values that provide various types of resolver information. keywords with values that provide various types of resolver information.
.Pp .Pp
On a normally configured system this file should not be necessary. On a normally configured system this file should not be necessary.
The only name server to be queried will be on the local machine, The only name server(s) to be queried will be on the local machine
or automatically configured using DHCP or a similar mechanism,
the domain name is determined from the host name, the domain name is determined from the host name,
and the domain search path is constructed from the domain name. and the domain search path is constructed from the domain name.
.Pp .Pp
The different configuration options are: The different configuration options are:
.Bl -tag -width nameserver .Bl -tag -width nameserver
.It Sy nameserver .It Sy nameserver
IPv4 or IPv6 address of a name server IPv4 or IPv6 address of a name server
that the resolver should query. that the resolver should query.
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.It Sy debug .It Sy debug
sets sets
.Dv RES_DEBUG .Dv RES_DEBUG
in _res.options. in _res.options.
.It Sy usevc .It Sy usevc
sets sets
.Dv RES_USEVC .Dv RES_USEVC
to use TCP instead of UDP for queries. to use TCP instead of UDP for queries.
.It Sy ndots: Ns Ar n .It Sy ndots : Ns Ar n
sets a threshold for the number of dots which must appear in a name given to sets a threshold for the number of dots which must appear in a name given to
.Fn res_query .Fn res_query
(see (see
.Xr resolver 3 ) .Xr resolver 3 )
before an before an
.Em initial absolute query .Em initial absolute query
will be made. will be made.
The default for The default for
.Em n .Em n
is is
.Dq 1 , .Dq 1 ,
meaning that if there are any dots in a name, the name meaning that if there are any dots in a name, the name
will be tried first as an absolute name before any will be tried first as an absolute name before any
.Em search list .Em search list
elements are appended to it. elements are appended to it.
.It Sy timeout: Ns Ar n .It Sy timeout : Ns Ar n
sets the initial amount of time the resolver will wait sets the initial amount of time the resolver will wait
for a response from a remote for a response from a remote
name server before retrying the query via a different name server. name server before retrying the query via a different name server.
The resolver may wait longer during subsequent retries The resolver may wait longer during subsequent retries
of the current query since an exponential back-off is applied to of the current query since an exponential back-off is applied to
the timeout value. the timeout value.
Measured in seconds, the default is Measured in seconds, the default is
.Dv RES_TIMEOUT , .Dv RES_TIMEOUT ,
the allowed maximum is the allowed maximum is
.Dv RES_MAXRETRANS .Dv RES_MAXRETRANS
(see (see
.In resolv.h ) . .In resolv.h ) .
.It Sy attempts: Ns Ar n .It Sy attempts : Ns Ar n
sets the number of times the resolver will send a query to each of sets the number of times the resolver will send a query to each of
its name servers its name servers
before giving up and returning an error to the calling application. before giving up and returning an error to the calling application.
The default is The default is
.Dv RES_DFLRETRY , .Dv RES_DFLRETRY ,
the allowed maximum is the allowed maximum is
.Dv RES_MAXRETRY .Dv RES_MAXRETRY
(see (see
.In resolv.h ) . .In resolv.h ) .
.It Sy no_tld_query .It Sy no_tld_query
tells the resolver not to attempt to resolve a top level domain name, that tells the resolver not to attempt to resolve a top level domain name, that
is, a name that contains no dots. is, a name that contains no dots.
Use of this option does not prevent Use of this option does not prevent
the resolver from obeying the standard the resolver from obeying the standard
.Sy domain .Sy domain
and and
.Sy search .Sy search
rules with the given name. rules with the given name.
.It Sy reload-period: Ns Ar n .It Sy reload-period : Ns Ar n
The resolver checks the modification time of The resolver checks the modification time of
.Pa /etc/resolv.conf .Pa /etc/resolv.conf
every every
.Ar n .Ar n
seconds. seconds.
If If
.Pa /etc/resolv.conf .Pa /etc/resolv.conf
has changed, it is automatically reloaded. has changed, it is automatically reloaded.
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