NSUPDATE(1) BIND 9 NSUPDATE(1)
NAME
nsupdate - dynamic DNS update utility
SYNOPSIS
nsupdate [-d] [-D] [-i] [-L level] [ [-g] | [-o] | [-l] | [-y
[hmac:]keyname:secret] | [-k keyfile] ] [ [-S] [-K tlskeyfile] [-E
tlscertfile] [-A tlscafile] [-H tlshostname] [-O] ] [-t timeout] [-u
udptimeout] [-r udpretries] [-v] [-T] [-P] [-V] [ [-4] | [-6] ] [file-
name]
DESCRIPTION
nsupdate is used to submit Dynamic DNS Update requests, as defined in ]8;;https://datatracker.ietf.org/doc/html/rfc2136.html\-
RFC 2136]8;;\, to a name server. This allows resource records to be added or
removed from a zone without manually editing the zone file. A single up-
date request can contain requests to add or remove more than one re-
source record.
Zones that are under dynamic control via nsupdate or a DHCP server
should not be edited by hand. Manual edits could conflict with dynamic
updates and cause data to be lost.
The resource records that are dynamically added or removed with nsupdate
must be in the same zone. Requests are sent to the zone's primary
server, which is identified by the MNAME field of the zone's SOA record.
Transaction signatures can be used to authenticate the Dynamic DNS up-
dates. These use the TSIG resource record type described in ]8;;https://datatracker.ietf.org/doc/html/rfc2845.html\RFC 2845]8;;\,
the SIG(0) record described in ]8;;https://datatracker.ietf.org/doc/html/rfc2535.html\RFC 2535]8;;\ and ]8;;https://datatracker.ietf.org/doc/html/rfc2931.html\RFC 2931]8;;\, or GSS-TSIG as de-
scribed in ]8;;https://datatracker.ietf.org/doc/html/rfc3645.html\RFC 3645]8;;\.
TSIG relies on a shared secret that should only be known to nsupdate and
the name server. For instance, suitable key and server statements are
added to /etc/bind/named.conf so that the name server can associate the
appropriate secret key and algorithm with the IP address of the client
application that is using TSIG authentication. ddns-confgen can generate
suitable configuration fragments. nsupdate uses the -y or -k options to
provide the TSIG shared secret; these options are mutually exclusive.
SIG(0) uses public key cryptography. To use a SIG(0) key, the public key
must be stored in a KEY record in a zone served by the name server.
GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode is switched
on with the -g flag. A non-standards-compliant variant of GSS-TSIG used
by Windows 2000 can be switched on with the -o flag.
OPTIONS
-4 This option sets use of IPv4 only.
-6 This option sets use of IPv6 only.
-A tlscafile
This option specifies the file of the certificate authorities
(CA) certificates (in PEM format) in order to verify the remote
server TLS certificate when using DNS-over-TLS (DoT), to achieve
Strict or Mutual TLS. When used, it will override the certifi-
cates from the global certificates store, which are otherwise
used by default when -S is enabled. This option can not be used
in conjuction with -O, and it implies -S.
-C Overrides the default resolv.conf file. This is only intended for
testing.
-d This option sets debug mode, which provides tracing information
about the update requests that are made and the replies received
from the name server.
-D This option sets extra debug mode.
-E tlscertfile
This option sets the certificate(s) file for authentication for
the DNS-over-TLS (DoT) transport to the remote server. The cer-
tificate chain file is expected to be in PEM format. This option
implies -S, and can only be used with -K.
-g This option enables standard GSS-TSIG mode.
-H tlshostname
This option makes nsupdate use the provided hostname during re-
mote server TLS certificate verification. Otherwise, the DNS
server name is used. This option implies -S.
-i This option forces interactive mode, even when standard input is
not a terminal.
-k keyfile
This option indicates the file containing the TSIG authentication
key. Keyfiles may be in two formats: a single file containing a
named.conf-format key statement, which may be generated automati-
cally by ddns-confgen; or a pair of files whose names are of the
format K{name}.+157.+{random}.key and K{name}.+157.+{random}.pri-
vate, which can be generated by dnssec-keygen. The -k option can
also be used to specify a SIG(0) key used to authenticate Dynamic
DNS update requests. In this case, the key specified is not an
HMAC-MD5 key.
-K tlskeyfile
This option sets the key file for authenticated encryption for
the DNS-over-TLS (DoT) transport with the remote server. The pri-
vate key file is expected to be in PEM format. This option im-
plies -S, and can only be used with -E.
-l This option sets local-host only mode, which sets the server ad-
dress to localhost (disabling the server so that the server ad-
dress cannot be overridden). Connections to the local server use
a TSIG key found in /run/session.key, which is automatically gen-
erated by named if any local primary zone has set update-policy
to local. The location of this key file can be overridden with
the -k option.
-L level
This option sets the logging debug level. If zero, logging is
disabled.
-o This option is deprecated. Previously, it enabled a non-stan-
dards-compliant variant of GSS-TSIG that was used by Windows
2000. Since that OS is now long past its end of life, this option
is now treated as a synonym for -g.
-O This option enables Opportunistic TLS. When used, the remote
peer's TLS certificate will not be verified. This option should
be used for debugging purposes only, and it is not recommended to
use it in production. This option can not be used in conjuction
with -A, and it implies -S.
-p port
This option sets the port to use for connections to a name
server. The default is 53.
-P This option prints the list of private BIND-specific resource
record types whose format is understood by nsupdate. See also the
-T option.
-r udpretries
This option sets the number of UDP retries. The default is 3. If
zero, only one update request is made.
-S This option indicates whether to use DNS-over-TLS (DoT) when
querying name servers specified by server servername port syntax
in the input file, and the primary server discovered through a
SOA request. When the -K and -E options are used, then the speci-
fied TLS client certificate and private key pair are used for au-
thentication (Mutual TLS). This option implies -v.
-t timeout
This option sets the maximum time an update request can take be-
fore it is aborted. The default is 300 seconds. If zero, the
timeout is disabled for TCP mode. For UDP mode, the option -u
takes precedence over this option, unless the option -u is set to
zero, in which case the interval is computed from the -t timeout
interval and the number of UDP retries. For UDP mode, the timeout
can not be disabled, and will be rounded up to 1 second in case
if both -t and -u are set to zero.
-T This option prints the list of IANA standard resource record
types whose format is understood by nsupdate. nsupdate exits af-
ter the lists are printed. The -T option can be combined with the
-P option.
Other types can be entered using TYPEXXXXX where XXXXX is the
decimal value of the type with no leading zeros. The rdata, if
present, is parsed using the UNKNOWN rdata format, (<backslash>
<hash> <space> <length> <space> <hexstring>).
-u udptimeout
This option sets the UDP retry interval. The default is 3 sec-
onds. If zero, the interval is computed from the timeout interval
and number of UDP retries.
-v This option specifies that TCP should be used even for small up-
date requests. By default, nsupdate uses UDP to send update re-
quests to the name server unless they are too large to fit in a
UDP request, in which case TCP is used. TCP may be preferable
when a batch of update requests is made.
-V This option prints the version number and exits.
-y [hmac:]keyname:secret
This option sets the literal TSIG authentication key. keyname is
the name of the key, and secret is the base64 encoded shared se-
cret. hmac is the name of the key algorithm; valid choices are
hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, or
hmac-sha512. If hmac is not specified, the default is hmac-md5,
or if MD5 was disabled, hmac-sha256.
NOTE: Use of the -y option is discouraged because the shared se-
cret is supplied as a command-line argument in clear text. This
may be visible in the output from ps1 or in a history file main-
tained by the user's shell.
INPUT FORMAT
nsupdate reads input from filename or standard input. Each command is
supplied on exactly one line of input. Some commands are for administra-
tive purposes; others are either update instructions or prerequisite
checks on the contents of the zone. These checks set conditions that
some name or set of resource records (RRset) either exists or is absent
from the zone. These conditions must be met if the entire update request
is to succeed. Updates are rejected if the tests for the prerequisite
conditions fail.
Every update request consists of zero or more prerequisites and zero or
more updates. This allows a suitably authenticated update request to
proceed if some specified resource records are either present or missing
from the zone. A blank input line (or the send command) causes the accu-
mulated commands to be sent as one Dynamic DNS update request to the
name server.
The command formats and their meanings are as follows:
server servername port
This command sends all dynamic update requests to the name server
servername. When no server statement is provided, nsupdate sends
updates to the primary server of the correct zone. The MNAME
field of that zone's SOA record identify the primary server for
that zone. port is the port number on servername where the dy-
namic update requests are sent. If no port number is specified,
the default DNS port number of 53 is used.
NOTE:
This command has no effect when GSS-TSIG is in use.
local address port
This command sends all dynamic update requests using the local
address. When no local statement is provided, nsupdate sends up-
dates using an address and port chosen by the system. port can
also be used to force requests to come from a specific port. If
no port number is specified, the system assigns one.
zone zonename
This command specifies that all updates are to be made to the
zone zonename. If no zone statement is provided, nsupdate at-
tempts to determine the correct zone to update based on the rest
of the input.
class classname
This command specifies the default class. If no class is speci-
fied, the default class is IN.
ttl seconds
This command specifies the default time-to-live, in seconds, for
records to be added. The value none clears the default TTL.
key hmac:keyname secret
This command specifies that all updates are to be TSIG-signed us-
ing the keyname-secret pair. If hmac is specified, it sets the
signing algorithm in use. The default is hmac-md5; if MD5 was
disabled, the default is hmac-sha256. The key command overrides
any key specified on the command line via -y or -k.
gsstsig
This command uses GSS-TSIG to sign the updates. This is equiva-
lent to specifying -g on the command line.
oldgsstsig
This command is deprecated and will be removed in a future re-
lease. Previously, it caused nsupdate to use the Windows 2000
version of GSS-TSIG to sign updates. It is now treated as a syn-
onym for gsstsig.
realm [realm_name]
When using GSS-TSIG, this command specifies the use of realm_name
rather than the default realm in krb5.conf. If no realm is speci-
fied, the saved realm is cleared.
check-names [boolean]
This command turns on or off check-names processing on records to
be added. Check-names has no effect on prerequisites or records
to be deleted. By default check-names processing is on. If
check-names processing fails, the record is not added to the UP-
DATE message.
check-svbc [boolean]
This command turns on or off check-svcb processing on records to
be added. Check-svcb has no effect on prerequisites or records
to be deleted. By default check-svcb processing is on. If
check-svcb processing fails, the record is not added to the UP-
DATE message.
lease time [keytime]
Set the EDNS Update Lease (UL) option to value to time and op-
tionally also set the key lease time to keytime in seconds. If
time is none the lease times are cleared.
prereq nxdomain domain-name
This command requires that no resource record of any type exist
with the name domain-name.
prereq yxdomain domain-name
This command requires that domain-name exist (as at least one re-
source record, of any type).
prereq nxrrset domain-name class type
This command requires that no resource record exist of the speci-
fied type, class, and domain-name. If class is omitted, IN (In-
ternet) is assumed.
prereq yxrrset domain-name class type
This command requires that a resource record of the specified
type, class and domain-name exist. If class is omitted, IN (in-
ternet) is assumed.
prereq yxrrset domain-name class type data
With this command, the data from each set of prerequisites of
this form sharing a common type, class, and domain-name are com-
bined to form a set of RRs. This set of RRs must exactly match
the set of RRs existing in the zone at the given type, class, and
domain-name. The data are written in the standard text represen-
tation of the resource record's RDATA.
update delete domain-name ttl class type data
This command deletes any resource records named domain-name. If
type and data are provided, only matching resource records are
removed. The Internet class is assumed if class is not supplied.
The ttl is ignored, and is only allowed for compatibility.
update add domain-name ttl class type data
This command adds a new resource record with the specified ttl,
class, and data.
show This command displays the current message, containing all of the
prerequisites and updates specified since the last send.
send This command sends the current message. This is equivalent to en-
tering a blank line.
answer This command displays the answer.
debug This command turns on debugging.
version
This command prints the version number.
help This command prints a list of commands.
Lines beginning with a semicolon (;) are comments and are ignored.
EXAMPLES
The examples below show how nsupdate can be used to insert and delete
resource records from the example.com zone. Notice that the input in
each example contains a trailing blank line, so that a group of commands
is sent as one dynamic update request to the primary name server for ex-
ample.com.
# nsupdate
> update delete oldhost.example.com A
> update add newhost.example.com 86400 A 172.16.1.1
> send
Any A records for oldhost.example.com are deleted, and an A record for
newhost.example.com with IP address 172.16.1.1 is added. The newly added
record has a TTL of 1 day (86400 seconds).
# nsupdate
> prereq nxdomain nickname.example.com
> update add nickname.example.com 86400 CNAME somehost.example.com
> send
The prerequisite condition tells the name server to verify that there
are no resource records of any type for nickname.example.com. If there
are, the update request fails. If this name does not exist, a CNAME for
it is added. This ensures that when the CNAME is added, it cannot con-
flict with the long-standing rule in ]8;;https://datatracker.ietf.org/doc/html/rfc1034.html\RFC 1034]8;;\ that a name must not exist
as any other record type if it exists as a CNAME. (The rule has been up-
dated for DNSSEC in ]8;;https://datatracker.ietf.org/doc/html/rfc2535.html\RFC 2535]8;;\ to allow CNAMEs to have RRSIG, DNSKEY, and
NSEC records.)
FILES
/etc/resolv.conf
Used to identify the default name server
/run/session.key
Sets the default TSIG key for use in local-only mode
K{name}.+157.+{random}.key
Base-64 encoding of the HMAC-MD5 key created by dnssec-keygen.
K{name}.+157.+{random}.private
Base-64 encoding of the HMAC-MD5 key created by dnssec-keygen.
SEE ALSO
]8;;https://datatracker.ietf.org/doc/html/rfc2136.html\RFC 2136]8;;\, ]8;;https://datatracker.ietf.org/doc/html/rfc3007.html\RFC 3007]8;;\, ]8;;https://datatracker.ietf.org/doc/html/rfc2104.html\RFC 2104]8;;\, ]8;;https://datatracker.ietf.org/doc/html/rfc2845.html\RFC 2845]8;;\, ]8;;https://datatracker.ietf.org/doc/html/rfc1034.html\RFC 1034]8;;\, ]8;;https://datatracker.ietf.org/doc/html/rfc2535.html\RFC 2535]8;;\, ]8;;https://datatracker.ietf.org/doc/html/rfc2931.html\RFC 2931]8;;\,
named(8), dnssec-keygen(8), tsig-keygen(8).
BUGS
The TSIG key is redundantly stored in two separate files. This is a con-
sequence of nsupdate using the DST library for its cryptographic opera-
tions, and may change in future releases.
AUTHOR
Internet Systems Consortium
COPYRIGHT
2025, Internet Systems Consortium
9.20.15-1~deb13u1-Debian 2025-10-18 NSUPDATE(1)
Generated by dwww version 1.16 on Tue Dec 16 04:49:34 CET 2025.