knsupdate – Dynamic DNS update utility


knsupdate [options] [filename]


This utility sends Dynamic DNS update messages to a DNS server. Update content is read from a file (if the parameter filename is given) or from the standard input.

The format of updates is textual and is made up of commands. Every command is placed on the separate line of the input. Lines starting with a semicolon are comments and are not processed.



Path to the file with knsupdate commands.



Enable debug messages.

-h, --help

Print the program help.

-k keyfile

Use the TSIG key stored in a file keyfile to authenticate the request. The file should contain the key in the same format, which is accepted by the -y option.

-p port

Set the port to use for connections to the server (if not explicitly specified in the update). The default is 53.

-r retries

The number of retries for UDP requests. The default is 3.

-t timeout

The total timeout (for all UDP update tries) of the update request in seconds. The default is 12. If set to zero, the timeout is infinite.


Use a TCP connection.

-V, --version

Print the program version.

-y [alg:]name:key

Use the TSIG key with a name name to authenticate the request. The alg part specifies the algorithm (the default is hmac-sha256) and key specifies the shared secret encoded in Base64.


server name [port]

Specifies a receiving server of the dynamic update message. The name parameter can be either a host name or an IP address. If the port is not specified, the default port is used. The default port value can be controlled using the -p program option.

local address [port]

Specifies outgoing address and port. If no local is specified, the address and port are set by the system automatically. The default port number is 0.

zone name

Specifies that all updates are done within a zone name. The zone name doesn't have a default and must be set explicitly.

origin name

Specifies fully qualified domain name suffix which is appended to non-fqd owners in update commands. The default is the terminal label (.).

class name

Sets name as the default class for all updates. If not used, the default class is IN.

ttl value

Sets value as the default TTL (in seconds). If not used, the default value is 3600.

key [alg:]name key

Specifies the TSIG key named name to authenticate the request. An optional alg algorithm can be specified. This command has the same effect as the program option -y.

[prereq] nxdomain name

Adds a prerequisite for a non-existing record owned by name.

[prereq] yxdomain name

Adds a prerequisite for an existing record owned by name.

[prereq] nxrrset name [class] type

Adds a prerequisite for a non-existing record of the type owned by name. Internet class is expected.

[prereq] yxrrset name [class] type [data]

Adds a prerequisite for an existing record of the type owned by name with optional data. Internet class is expected.

[update] add name [ttl] [class] type data

Adds a request to add a new resource record into the zone. Please note that if the name is not fully qualified domain name, the current origin name is appended to it.

[update] del[ete] name [ttl] [class] [type] [data]

Adds a request to remove all (or matching class, type or data) resource records from the zone. There is the same requirement for the name parameter as in update add command. The ttl item is ignored.


Displays current content of the update message.


Sends the current update message and cleans the list of updates.


Displays the last answer from the server.


Enable debugging. This command has the same meaning as the -d program option.


End the program.


Options -k and -y can not be used simultaneously.

Neither tsig-keygen(8) nor dnssec-keygen(1) keyfile formats are supported. Use keymgr(8) to construct a string for -y or the file passed to -k.

Zone name/server guessing is not supported if the zone name/server is not specified.

An empty line doesn't send the update.

Interactive mode

The utility provides interactive mode with basic line editing functionality, command completion, and command history.

Interactive mode behavior can be customized in ~/.editrc. Refer to editrc(5) for details.

Command history is saved in ~/.knsupdate_history.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


  1. Send one update of the zone to the server The update contains two new records:

    $ knsupdate
    knsupdate> server
    knsupdate> zone
    knsupdate> origin
    knsupdate> ttl 3600
    knsupdate> add 7200 A
    knsupdate> add test2 TXT "hello"
    knsupdate> show
    knsupdate> send
    knsupdate> answer
    knsupdate> exit

See Also

kdig(1), khost(1), keymgr(8), editrc(5).