path: root/usr.bin/dig/dig.1

.\" $OpenBSD: dig.1,v 1.5 2021/03/12 05:18:01 jsg Exp $
.\"
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.Dd $Mdocdate: March 12 2021 $
.Dt DIG 1
.Os
.Sh NAME
.Nm dig
.Nd DNS lookup utility
.Sh SYNOPSIS
.Nm
.Op Pf @ Ar server
.Op Fl 46hiuv
.Op Fl b Ar sourceaddr Ns Op Pf # Ar port
.Op Fl c Ar class
.Op Fl f Ar file
.Op Fl k Ar keyfile
.Op Fl p Ar port
.Op Fl q Ar name
.Op Fl t Ar type
.Op Fl x Ar addr
.Op Fl y Oo Ar hmac : Oc Ns Ar name : Ns Ar key
.Op Ar name
.Op Ar type
.Op Ar class
.Op Pf + Ar queryopt ...
.Sh DESCRIPTION
The
.Nm
command is a flexible tool for interrogating DNS name servers.
It performs DNS lookups and displays the answers that are returned from the name
servers that were queried.
Although
.Nm
is normally used with command line arguments, it also has a batch mode of
operation for reading lookup requests from a file.
When no command line arguments or options are given,
.Nm
will perform an NS query for '.' (the root).
.Pp
A typical invocation of
.Nm
looks like:
.Pp
.Dl dig @server [options] name type [class] [+queryopt]
.Bl -tag -width +queryopt
.It Pf @ Ar server
The name or IP address of the name server to query.
When the argument is a hostname,
.Nm
resolves that name before querying that name server.
If no
.Ar server
argument is provided,
.Nm
will try each of the servers listed in
.Xr resolv.conf 5 .
If no usable addresses are found,
.Nm
will send the query to the local host.
The reply from the name server that responds is displayed.
.It Ar name
The name of the resource record that is to be looked up.
.It Ar type
The type of query, as documented for
.Fl t .
The default is
.Cm A .
.It Ar class
The query class, as documented for
.Fl c .
The default is
.Cm IN .
.It Pf + Ar queryopt
One or more query options,
as documented in
.Sx QUERY OPTIONS ,
below.
.El
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl 4
Use IPv4 only.
.It Fl 6
Use IPv6 only.
.It Fl b Ar sourceaddr Ns Op Pf # Ar port
Set the source IP address of the query, which is useful on machines
with multiple interfaces.
The
.Ar sourceaddr
must be a valid address on one of the host's network interfaces, or
"0.0.0.0" or "::". An optional port may be specified by appending
"#<port>".
.It Fl c Ar class
Set the query class.
The default is
.Cm IN ;
other classes are
.Cm HS
for Hesiod records and
.Cm CH
for Chaosnet records.
.It Fl f Ar file
Batch mode:
.Nm
reads a list of lookup requests to process from the given
.Ar file .
Each line in the file should be organized in the same way they would be
presented as queries to
.Nm
using the command-line interface.
.It Fl h
Display a brief summary of command line arguments and options.
.It Fl i
Do reverse IPv6 lookups using the obsolete RFC 1886 IP6.INT domain, which is no
longer in use.
Obsolete bit string label queries (RFC 2874) are not attempted.
.It Fl k Ar keyfile
Sign queries using TSIG.
The format of the
.Ar keyfile
is as follows:
.Bd -literal -offset indent
key "keyname" {
	algorithm hmac;
	secret "base64-secret";
};
.Ed
.Pp
.Ar keyname
is the name of the key, and
.Ar base64-secret
is the base64-encoded shared secret.
.Ar hmac
is the name of the key algorithm;
valid choices are
.Cm hmac-sha1 ,
.Cm hmac-sha224 ,
.Cm hmac-sha256 ,
.Cm hmac-sha384 ,
and
.Cm hmac-sha512 .
.It Fl p Ar port
Send the query to a non-standard port on the server, instead of the default port
53.
This option would be used to test a name server that has been configured to
listen for queries on a non-standard port number.
.It Fl q Ar name
The domain name to query.
This is useful to distinguish the
.Ar name
from other arguments.
.It Fl t Ar type
The resource record type to query.
It can be any valid query type.
If it is a resource record type supported in BIND 9, it can be given by the
type mnemonic (such as
.Cm NS
or
.Cm AAAA ) .
The default query type is
.Cm A ,
unless the
.Fl x
option is supplied to indicate a reverse lookup.
A zone transfer can be requested by specifying a type of
.Cm AXFR .
When an incremental zone transfer is required, set the
.Ar type
to
.Cm IXFR Ns = Ns Ar N .
The incremental zone transfer will contain the changes made to the zone since
the serial number in the zone's SOA record was
.Ar N .
.Pp
All resource record types can be expressed as
.Cm TYPE Ns Ar nn ,
where
.Ar nn
is the number of the type.
If the resource record type is not supported in BIND 9, the result will be
displayed as described in RFC 3597.
.It Fl u
Print query times in microseconds instead of milliseconds.
.It Fl v
Print the version number and exit.
.It Fl x Ar addr
Simplified reverse lookups, for mapping addresses to names.
The
.Ar addr
is an IPv4 address in dotted-decimal notation, or a colon-delimited IPv6
address.
When the
.Fl x
is used, there is no need to provide the
.Ar name ,
.Ar class
and
.Ar type
arguments.
.Nm
automatically performs a lookup for a name like
.Ql 94.2.0.192.in-addr.arpa
and sets the query type and class to
.Cm PTR
and
.Cm IN
respectively.
IPv6 addresses are looked up using nibble format under the IP6.ARPA domain
(but see also the
.Fl i
option).
.It Fl y Xo
.Op Ar hmac : Ns
.Ar keyname : Ns
.Ar secret
.Xc
Sign queries using TSIG with the given authentication key.
.Ar keyname
is the name of the key, and
.Ar secret
is the base64 encoded shared secret.
.Ar hmac
is the name of the key algorithm;
valid choices are
.Cm hmac-sha1 ,
.Cm hmac-sha224 ,
.Cm hmac-sha256 ,
.Cm hmac-sha384 ,
and
.Cm hmac-sha512 .
If
.Ar hmac
is not specified, the default is
.Cm hmac-sha256 .
.Pp
NOTE: You should use the
.Fl k
option and
avoid the
.Fl y
option, because
with
.Fl y
the shared secret is supplied as a command line argument in clear text.
This may be visible in the output from
.Xr ps 1
or in a history file maintained by the user's shell.
.El
.Pp
The
.Cm IN
and
.Cm CH
class names overlap with the IN and CH top level domain names.
Either use the
.Fl t
and
.Fl c
options to specify the type and class, use the
.Fl q
to specify the domain name, or use "IN." and "CH." when looking up these top
level domains.
.Sh QUERY OPTIONS
.Nm
provides a number of query options which affect the way in which lookups are
made and the results displayed.
Some of
these set or reset flag bits in the query header, some determine which sections
of the answer get printed, and others determine the timeout and retry
strategies.
.Pp
Each query option is identified by a keyword preceded by a plus sign
.Pq Cm + .
Some keywords set or reset an option.
These may be preceded by the string
.Cm no
to negate the meaning of that keyword.
Other keywords assign values to options like the timeout interval.
They have the form
.Cm + Ns Ar keyword Ns = Ns Ar value .
Keywords may be abbreviated, provided the abbreviation is unambiguous; for
example,
.Cm +cd
is equivalent
to
.Cm +cdflag .
The query options are:
.Bl -tag -width Ds
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm aaflag
.Xc
A synonym for
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm aaonly .
.Xc
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm aaonly
.Xc
Set the "aa" flag in the query (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm additional
.Xc
Display the additional section of a reply (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm adflag
.Xc
Set the AD (authentic data) bit in the query (on by default).
This requests the server to return whether all of the answer and authority
sections have all been validated as secure according to the security policy of
the server.
AD=1 indicates that all records have been validated as secure and the answer is
not from an OPT-OUT range.
AD=0 indicates that some part of the answer was insecure or not validated.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm all
.Xc
Set or clear all display flags.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm answer
.Xc
Display the answer section of a reply (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm authority
.Xc
Display the authority section of a reply (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm besteffort
.Xc
Attempt to display the contents of messages which are malformed (on by
default).
.It Cm +bufsize Ns = Ns Ar #
Set the UDP message buffer size advertised using EDNS0 to
.Ar #
bytes.
The maximum and minimum sizes of this buffer are 65535 and 0 respectively.
Values outside this range are rounded up or down appropriately.
Values other than zero will cause an EDNS query to be sent.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm cdflag
.Xc
Set the CD (checking disabled) bit in the query (off by default).
This requests the server to not perform DNSSEC validation of responses.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm class
.Xc
Display the CLASS when printing the record (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm cmd
.Xc
Print an initial comment identifying the version of
.Nm
and the query options that have been applied (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm comments
.Xc
Display comment lines in the output (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm cookie Ns
.Op = Ns Ar value
.Xc
Send a COOKIE EDNS option, containing an optional
.Ar value
(off by default).
Replaying a COOKIE from a previous response will allow the server to
identify a previous client.
.Pp
.Cm +cookie
is automatically set when
.Cm +trace
is in use, to better emulate the default queries from a name server.
.Pp
This option was formerly called
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm sit
.Xc
(Server Identity Token).
In BIND 9.10.0 through BIND 9.10.2,
it sent the experimental option code 65001.
This was changed to option code 10 in BIND 9.10.3 when the DNS
COOKIE option was allocated.
.Pp
The
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm sit
.Xc
option is now deprecated, but has been retained as a synonym for
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm cookie
.Xc
for backward compatibility within the BIND 9.10 branch.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm crypto
.Xc
Display cryptographic fields in DNSSEC records (on by default).
The contents of these field are unnecessary to debug most DNSSEC validation
failures and removing them makes it easier to see the common failures.
When omitted they are replaced by the string "[omitted]" or in the DNSKEY case
the key id is displayed as the replacement, e.g. "[ key id = value ]".
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm defname
.Xc
Deprecated, treated as a synonym for
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm search
.Xc .
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm dnssec
.Xc
Request DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT
record in the additional section of the query (off by default).
.It Cm +domain Ns = Ns Ar name
Set the search list to contain the single domain
.Ar name ,
as if specified in a
.Ic domain
directive in
.Xr resolv.conf 5 ,
and enable search list processing as if the
.Cm +search
option were given (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm edns Ns
.Op = Ns Ar #
.Xc
Use EDNS in the query (on by default).
A version may also be specified, from 0 (the default) to 255.
.Cm +noedns
disables EDNS and clears the remembered version.
.It Cm +ednsflags Ns Op = Ns Ar #
Set the must-be-zero EDNS flags bits (Z bits)
to the specified value (0 by default).
Decimal, hex and octal encodings are accepted.
Setting a named flag (e.g. DO) will silently be ignored.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm ednsnegotiation
.Xc
Enable EDNS version negotiation (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm ednsopt Ns
.Op = Ns Ar code Ns Op : Ns Ar value
.Xc
Specify EDNS option with code point
.Ar code
and optionally payload of
.Ar value
as a hexadecimal string.
.Ar code
can be
either an EDNS option name (for example,
.Cm NSID
or
.Cm ECS ) ,
or an arbitrary numeric value.
.Cm +noednsopt
clears the EDNS options to be sent.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm expire
.Xc
Send an EDNS Expire option (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm fail
.Xc
Do not try the next server if you receive a SERVFAIL.
This option is on by default,
which is the reverse of normal stub resolver behavior.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm identify
.Xc
Show the IP address and port number that supplied the answer (off by default).
This option has no effect unless the
.Cm +short
option is enabled.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm idnout
.Xc
Convert puny code on output.
This version of
.Nm
does not support IDN.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm ignore
.Xc
Ignore truncation in UDP responses.
This option is off by default, which means truncated responses
cause retrying with TCP.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm keepopen
.Xc
Keep the TCP socket open between queries and reuse it.
This option is off by default, which means that a new TCP socket
is created for each lookup.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm multiline
.Xc
Print records like the SOA records in a verbose multi-line format with
human-readable comments.
This option is off by default, which means that each record is
printed on a single line to facilitate machine parsing of the
.Nm
output.
.It Cm +ndots Ns = Ns Ar #
Set the number of dots that have to appear in
.Ar name
to
.Ar #
for it to be considered absolute.
The default value is that defined using the ndots statement in
.Xr resolv.conf 5 ,
or 1 if no ndots statement is present.
Names with fewer dots are interpreted as relative names and will be searched
for in the domains listed in the
.Cm search
or
.Cm domain
directive in
.Xr resolv.conf 5
if
.Cm +search
is set.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm nsid
.Xc
Include an EDNS name server ID request when sending a query (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm nssearch
.Xc
Attempt to find the authoritative name servers for the zone
containing the name being looked up and display the SOA record
that each name server has for the zone (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm onesoa
.Xc
Print only one (starting) SOA record when performing an
.Cm AXFR .
This option is off by default, which means that both the starting
and the ending SOA records are printed.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm opcode Ns = Ns
.Ar #
.Xc
Set or restore the DNS message opcode to the specified value,
which can be
.Cm QUERY Pq the default ,
.Cm IQUERY ,
.Cm STATUS ,
.Cm NOTIFY ,
.Cm UPDATE ,
or an integer number in the range from 0 to 15.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm qr
.Xc
Print the query as it is sent (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm question
.Xc
Print the question section of a query as a comment when an answer
is returned (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm rdflag
.Xc
A synonym for
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm recurse
.Xc .
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm recurse
.Xc
Set the RD (recursion desired) bit in the query (on by default).
Recursion is automatically disabled when the
.Cm +nssearch
or
.Cm +trace
query options are used.
.It Cm +retry Ns = Ns Ar #
Set the number of times to retry UDP queries to server to
.Ar # .
The default is 2.
Unlike
.Cm +tries ,
this does not include the initial query.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm rrcomments
.Xc
Display per-record comments in the output (for example,
human-readable key information about DNSKEY records).
The default is
.Cm +rrcomments
if
.Cm +multiline
mode is active or
.Cm +norrcomments
otherwise.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm search
.Xc
Use the search list defined by the searchlist or domain directive in
.Xr resolv.conf 5 ,
if any (off by default).
\&'ndots' from
.Xr resolv.conf 5
(default 1), which may be overridden by
.Cm +ndots ,
determines if the name will be treated as relative or not and hence whether a
search is eventually performed or not.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm short
.Xc
Provide a terse answer (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm showsearch
.Xc
Perform a search showing intermediate results (off by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm split Ns = Ns Ar #
.Xc
Split long hex- or base64-formatted fields in resource records into chunks of
.Ar #
characters (where
.Ar #
is rounded up to the nearest multiple of 4).
.Cm +nosplit
or
.Cm +split Ns =0
causes fields not to be split at all.
The default is 56 characters, or 44 characters when
.Cm +multiline
mode is active.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm stats
.Xc
Print statistics:
when the query was made, the size of the reply and so on (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm subnet Ns = Ns
.Ar addr Ns
.Op / Ns Ar prefix
.Xc
Send an EDNS Client Subnet option with the specified IP address or
network prefix (off by default).
.Pp
.Nm
.Cm +subnet Ns =0.0.0.0/0,
or simply
.Nm
.Cm +subnet Ns =0
for short, sends an EDNS CLIENT-SUBNET option with an empty address and a
source prefix-length of zero, which signals a resolver that the client's address
information must
.Em not
be used when resolving this query.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm tcp
.Xc
Use TCP when querying name servers (off by default).
.Cm IXFR Ns = Ns Ar N
queries use TCP unless it is explicitly disabled with
.Cm +notcp .
.Cm AXFR
queries always use TCP.
.It Cm +timeout Ns = Ns Ar #
Set the timeout for a query to
.Ar #
seconds.
The default is 5 seconds for UDP and 10 seconds for TCP.
An attempt to set
.Ar #
to less than 1 will result in a query timeout of 1 second being applied.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm trace
.Xc
Trace the delegation path from the root name servers for the name
being looked up (off by default).
.Pp
When tracing is enabled,
.Nm
makes iterative queries to resolve the name being looked up.
It will follow referrals from the root servers, showing the answer from each
server that was used to resolve the lookup.
.Pp
If @server is also specified, it affects only the initial query for the root
zone name servers.
.Pp
.Cm +dnssec
is also set when
.Cm +trace
is set to better emulate the default queries from a name server.
.It Cm +tries Ns = Ns Ar #
Set the number of times to try UDP queries to server to
.Ar # .
The default is 3.
If
.Ar #
is less than or equal to zero, the number of tries is silently rounded up to 1.
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm ttlid
.Xc
Display the TTL when printing the record (on by default).
.It Xo
.Cm + Ns
.Op Cm no Ns
.Cm vc
.Xc
Use TCP when querying name servers.
This alternate syntax to
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm tcp
.Xc
is provided for backwards compatibility.
The "vc" stands for "virtual circuit".
.El
.Sh MULTIPLE QUERIES
The BIND 9 implementation of
.Nm
supports specifying multiple queries on the command line (in addition to
supporting the
.Fl f
batch file option).
Each of those queries can be supplied with its own set of flags, options and
query options.
.Pp
In this case, each
.Ar query
argument represent an individual query in the command-line syntax described
above.
Each consists of any of the standard options and flags, the name to be looked
up, an optional query type and class and any query options that should be
applied to that query.
.Pp
A global set of query options, which should be applied to all queries, can
also be supplied.
These global query options must precede the first tuple of name, class, type,
options, flags, and query options supplied on the command line.
Any global query options (except the
.Xo
.Cm + Ns
.Op Cm no Ns
.Cm cmd
.Xc
option) can be overridden by a query-specific set of query options.
For example:
.Bd -literal -offset indent
dig +qr www.isc.org any -x 127.0.0.1 isc.org ns +noqr
.Ed
.Pp
shows how
.Nm
could be used from the command line to make three lookups: an ANY query for
www.isc.org, a reverse lookup of 127.0.0.1 and a query for the NS records of
isc.org.
A global query option of
.Cm +qr
is applied, so that
.Nm
shows the initial query it made for each lookup.
The final query has a local query option of
.Cm +noqr
which means that
.Nm
will not print the initial query when it looks up the NS records for
isc.org.
.Sh FILES
.Bl -tag -width Ds
.It Pa /etc/resolv.conf
Resolver configuration file.
.El
.Sh SEE ALSO
.Xr host 1 ,
.Xr resolv.conf 5
.Sh STANDARDS
.Rs
.%A P. Mockapetris
.%D November 1987
.%R RFC 1035
.%T Domain Names - Implementation and Specification
.Re
.Sh AUTHORS
.An -nosplit
.An Internet Systems Consortium, Inc .
.Sh BUGS
There are probably too many query options.