# phpman > man > NSUPDATE(1) [NSUPDATE(1)](https://www.chedong.com/phpMan.php/man/NSUPDATE/1/markdown) BIND 9 [NSUPDATE(1)](https://www.chedong.com/phpMan.php/man/NSUPDATE/1/markdown) ## NAME nsupdate - dynamic DNS update utility ## SYNOPSIS **nsupdate** [**-d**] [**-D**] [**-i**] [**-L** level] [ [**-g**] | [**-o**] | [**-l**] | [**-y** [hmac:]keyname:secret] | [**-k** keyfile] ] [**-t** timeout] [**-u** udptimeout] [**-r** udpretries] [**-v**] [**-T**] [**-P**] [**-V**] [ [**-4**] | [**-6**] ] [filename] ## DESCRIPTION **nsupdate** is used to submit Dynamic DNS Update requests, as defined in _RFC_ _2136_, to a name server. This allows resource records to be added or removed from a zone without manually editing the zone file. A single update request can contain requests to add or remove more than one resource 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 updates. These use the TSIG resource record type described in _RFC_ _2845_, the [SIG(0)](https://www.chedong.com/phpMan.php/man/SIG/0/markdown) record described in _RFC_ _2535_ and _RFC_ _2931_, or GSS-TSIG as described in _RFC_ _3645_. 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 con‐ figuration fragments. **nsupdate** uses the _-y_ or _-k_ options to provide the TSIG shared secret; these options are mutually exclusive. [SIG(0)](https://www.chedong.com/phpMan.php/man/SIG/0/markdown) uses public key cryptography. To use a [SIG(0)](https://www.chedong.com/phpMan.php/man/SIG/0/markdown) 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 ### -6 ### -C ### -d quests that are made and the replies received from the name server. ### -D ### -g ### -i ### -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 automatically by **ddns-confgen**; or a pair of files whose names are of the format **K{name}.+157.+{random}.key** and **K{name}.+157.+{random}.private**, which can be generated by **dnssec-keygen**. The _-k_ option can also be used to specify a [SIG(0)](https://www.chedong.com/phpMan.php/man/SIG/0/markdown) key used to authenticate Dynamic DNS update requests. In this case, the key specified is not an HMAC-MD5 key. ### -l (disabling the **server** so that the server address 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 2000. ### -p port This option sets the port to use for connections to a name server. The default is 53. ### -P mat 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. ### -t timeout This option sets the maximum time an update request can take before 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 derstood by **nsupdate**. **nsupdate** exits after 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, ( ). ### -u udptimeout This option sets the UDP retry interval. The default is 3 seconds. If zero, the inter‐ val is computed from the timeout interval and number of UDP retries. ### -v fault, **nsupdate** uses UDP to send update requests 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 ### -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 secret. **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 dis‐ abled, **hmac-sha256**. NOTE: Use of the _-y_ option is discouraged because the shared secret is supplied as a command-line argument in clear text. This may be visible in the output from ps1 or in a history file maintained 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 administrative purposes; others are either update in‐ structions 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 accumulated 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 cor‐ rect 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 dynamic 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 updates 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** attempts 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 specified, 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 using 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 equivalent to specifying _-g_ on the command line. ### oldgsstsig This command uses the Windows 2000 version of GSS-TSIG to sign the updates. This is equivalent to specifying _-o_ on the command line. **realm** **[realm**___**name]** When using GSS-TSIG, this command specifies the use of **realm**___**name** rather than the de‐ fault realm in **krb5.conf**. If no realm is specified, 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 UPDATE message. ### prereq nxdomain domain-name This command requires that no resource record of any type exist with the name **do**‐‐ **main-name**. ### prereq yxdomain domain-name This command requires that **domain-name** exist (as at least one resource record, of any type). ### prereq nxrrset domain-name class type This command requires that no resource record exist of the specified **type**, **class**, and **domain-name**. If **class** is omitted, IN (Internet) is assumed. ### prereq yxrrset domain-name class type This command requires that a resource record of the specified **type**, **class** and **do**‐‐ **main-name** exist. If **class** is omitted, IN (internet) is assumed. ### prereq yxrrset domain-name class type data With this command, the **data** from each set of prerequisites of this form sharing a com‐ mon **type**, **class**, and **domain-name** are combined 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 representation 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 pro‐ vided, 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 up‐ dates specified since the last send. **send** This command sends the current message. This is equivalent to entering 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 **example.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 sec‐ onds). # 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 conflict with the long-standing rule in _RFC_ _1034_ that a name must not exist as any other record type if it exists as a CNAME. (The rule has been updated for DNSSEC in _RFC_ _2535_ to al‐ low 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 _RFC_ _2136_, _RFC_ _3007_, _RFC_ _2104_, _RFC_ _2845_, _RFC_ _1034_, _RFC_ _2535_, _RFC_ _2931_, [**named(8)](https://www.chedong.com/phpMan.php/man/named/8/markdown)**, **dnssec-key**‐‐ [**gen(8)](https://www.chedong.com/phpMan.php/man/gen/8/markdown)**, [**tsig-keygen(8)](https://www.chedong.com/phpMan.php/man/tsig-keygen/8/markdown)**. ## BUGS The TSIG key is redundantly stored in two separate files. This is a consequence of **nsupdate** using the DST library for its cryptographic operations, and may change in future releases. ## AUTHOR Internet Systems Consortium ## COPYRIGHT 2026, Internet Systems Consortium 9.18.39-0ubuntu0.22.04.4-Ubuntu 2025-08-13 [NSUPDATE(1)](https://www.chedong.com/phpMan.php/man/NSUPDATE/1/markdown)