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## 10. Network protocol information

Since May 2002, this protocol has an official port number from IANA, which is 3493. The old number (3305) was a relic of the original code’s ancestry, and conflicted with other services. Version 0.50.0 and up use 3493 by default.

This protocol runs over TCP. UDP support was dropped in July 2003. It had been deprecated for some time and was only capable of the simplest query commands as authentication is impossible over a UDP socket.

A C library, named `libupsclient`, that implements this protocol, is provided in both static and shared version to help the client application development, and is extensively used by client programs delivered by the Network UPS Tools project.

Other bindings maintained in the NUT code base or in its orbit, such as the C++ library `libnutclient`, a Python `PyNUTClient` module, a PERL `UPS::Nut` module, and a Java `jNut` client, are also available (but may lag behind in completeness of the protocol support). Numerous third-party implementations for other languages also exist, with some related projects listed on the NUT web site pages.

### 10.1. Old command removal notice

Before version 1.5.0, a number of old commands were supported. These have been removed from the specification. For more information, consult an older version of the software.

### 10.2. Command reference

Multi-word elements are contained within "quotes" for easier parsing. Embedded quotes are escaped with backslashes. Embedded backslashes are also escaped by representing them as \\. This protocol is intended to be interpreted with parseconf (NUT parser) or something similar.

### 10.3. Revision history

Here’s a table to present the various changes that happened to the NUT network protocol, over the time:

Protocol version | NUT version | Description
--- | --- | ---
1.0 | < 1.5.0 | Original protocol (legacy version)
1.1 | >= 1.5.0 | Original protocol (without old commands)
1.2 | >= 2.6.4 | Add "LIST CLIENT" and "NETVER" commands
Add ranges of values for writable variables
1.3 | >= 2.8.0 | Add "cmdparam" to "INSTCMD"
Add "TRACKING" commands (GET, SET)
Add "PRIMARY" as alias to older "MASTER" (implementation tested to be backwards compatible in `upsd` and `upsmon`)
Add "PROTVER" as alias to older "NETVER"

### Note

Any new version of the protocol implies an update of `NUT_NETVERSION` in configure.ac file.

ERRATA: Earlier revisions of this table mistakenly mentioned `LIST CLIENTS` as added since 2.6.4. The actual added command was `LIST CLIENT` (no `S`) as documented in its section below.

### 10.4. GET

Retrieve a single response from the server.

Possible sub-commands:

#### NUMLOGINS

Form:

    GET NUMLOGINS <upsname>
    GET NUMLOGINS su700

Response:

    NUMLOGINS <upsname> <value>
    NUMLOGINS su700 1

<value> is the number of clients which have done LOGIN for this UPS. This is used by the upsmon in primary mode to determine how many clients are still connected when starting the shutdown process.

This replaces the old "REQ NUMLOGINS" command.

See also `LIST CLIENT <upsname>` to get the actual list of connected clients.

#### UPSDESC

Form:

    GET UPSDESC <upsname>
    GET UPSDESC su700

Response:

    UPSDESC <upsname> "<description>"
    UPSDESC su700 "Development box"

<description> is the value of "desc=" from ups.conf for this UPS. If it is not set, upsd will return "Unavailable".

This can be used to provide human-readable descriptions instead of a cryptic "upsname@hostname" string.

#### VAR

Form:

    GET VAR <upsname> <varname>
    GET VAR su700 ups.status

Response:

    VAR <upsname> <varname> "<value>"
    VAR su700 ups.status "OL"

This replaces the old "REQ" command.

#### TYPE

Form:

    GET TYPE <upsname> <varname>
    GET TYPE su700 input.transfer.low

Response:

    TYPE <upsname> <varname> <type>...
    TYPE su700 input.transfer.low ENUM

<type> can be several values, and multiple words may be returned:

- RW: this variable may be set to another value with SET
- ENUM: an enumerated type, which supports a few specific values
- STRING:n: this is a string of maximum length n
- RANGE: this is an numeric, either integer or float, comprised in the range (see LIST RANGE)
- NUMBER: this is a simple numeric value, either integer or float

ENUM, STRING and RANGE are usually associated with RW, but not always. The default <type>, when omitted, is numeric, so either integer or float. Each driver is then responsible for handling values as either integer or float.

Note that float values are expressed using decimal (base 10) english-based representation, so using a dot, in non-scientific notation. So hexadecimal, exponents, and comma for thousands separator are forbidden. For example: "1200.20" is valid, while "1,200.20" and "1200,20" and "1.2e4" are invalid.

This replaces the old "VARTYPE" command.

#### DESC

Form:

    GET DESC <upsname> <varname>
    GET DESC su700 ups.status

Response:

    DESC <upsname> <varname> "<description>"
    DESC su700 ups.status "UPS status"

<description> is a string that gives a brief explanation of the named variable. upsd may return "Unavailable" if the file which provides this description is not installed.

Different versions of this file may be used in some situations to provide for localization and internationalization.

This replaces the old "VARDESC" command.

#### CMDDESC

Form:

    GET CMDDESC <upsname> <cmdname>
    GET CMDDESC su700 load.on

Response:

    CMDDESC <upsname> <cmdname> "<description>"
    CMDDESC su700 load.on "Turn on the load immediately"

This is like DESC above, but it applies to the instant commands.

This replaces the old "INSTCMDDESC" command.

#### TRACKING

Form:

    GET TRACKING      (activation status of TRACKING)
    GET TRACKING <id> (execution status of a command / setvar)
    GET TRACKING 1bd31808-cb49-4aec-9d75-d056e6f018d2

Response:

    ON                   (TRACKING feature is enabled)
    OFF                  (TRACKING feature is disabled)
    PENDING              (command execution is pending)
    SUCCESS              (command was successfully executed)
    ERR UNKNOWN          (command execution failed with unknown error)
    ERR INVALID-ARGUMENT (command execution failed due to missing or invalid argument)
    ERR FAILED           (command execution failed)

### 10.5. LIST

The LIST functions all share a common container format. They will return "BEGIN LIST" and then repeat the initial query. The list then follows, with as many lines are necessary to convey it. "END LIST" with the initial query attached then follows.

The formatting may seem a bit redundant, but it makes a different form of client possible. You can send a LIST query and then go off and wait for it to get back to you. When it arrives, you don’t need complicated state machines to remember which list is which.

#### UPS

Form:

    LIST UPS

Response:

    BEGIN LIST UPS
    UPS <upsname> "<description>"
    ...
    END LIST UPS

    BEGIN LIST UPS
    UPS su700 "Development box"
    END LIST UPS

<upsname> is a name from ups.conf, and <description> is the value of desc= from ups.conf, if available. It will be set to "Unavailable" otherwise.

This can be used to determine what values of <upsname> are valid before calling other functions on the server. This is also a good way to handle situations where a single upsd supports multiple drivers.

Clients which perform a UPS discovery process may find this useful.

#### VAR

Form:

    LIST VAR <upsname>
    LIST VAR su700

Response:

    BEGIN LIST VAR <upsname>
    VAR <upsname> <varname> "<value>"
    ...
    END LIST VAR <upsname>

    BEGIN LIST VAR su700
    VAR su700 ups.mfr "APC"
    VAR su700 ups.mfr.date "10/17/96"
    ...
    END LIST VAR su700

This replaces the old "LISTVARS" command.

#### RW

Form:

    LIST RW <upsname>
    LIST RW su700

Response:

    BEGIN LIST RW <upsname>
    RW <upsname> <varname> "<value>"
    ...
    END LIST RW <upsname>

    BEGIN LIST RW su700
    RW su700 output.voltage.nominal "115"
    RW su700 ups.delay.shutdown "020"
    ...
    END LIST RW su700

This replaces the old "LISTRW" command.

#### CMD

Form:

    LIST CMD <upsname>
    LIST CMD su700

Response:

    BEGIN LIST CMD <upsname>
    CMD <upsname> <cmdname>
    ...
    END LIST CMD <cmdname>

    BEGIN LIST CMD su700
    CMD su700 load.on
    CMD su700 test.panel.start
    ...
    END LIST CMD su700

This replaces the old "LISTINSTCMD" command.

#### ENUM

Form:

    LIST ENUM <upsname> <varname>
    LIST ENUM su700 input.transfer.low

Response:

    BEGIN LIST ENUM <upsname> <varname>
    ENUM <upsname> <varname> "<value>"
    ...
    END LIST ENUM <upsname> <varname>

    BEGIN LIST ENUM su700 input.transfer.low
    ENUM su700 input.transfer.low "103"
    ENUM su700 input.transfer.low "100"
    ...
    END LIST ENUM su700 input.transfer.low

This replaces the old "ENUM" command.

### Note

This does not support the old "SELECTED" notation. You must request the current value separately.

#### RANGE

Form:

    LIST RANGE <upsname> <varname>
    LIST RANGE su700 input.transfer.low

Response:

    BEGIN LIST RANGE <upsname> <varname>
    RANGE <upsname> <varname> "<min>" "<max>"
    ...
    END LIST RANGE <upsname> <varname>

    BEGIN LIST RANGE su700 input.transfer.low
    RANGE su700 input.transfer.low "90" "100"
    RANGE su700 input.transfer.low "102" "105"
    ...
    END LIST RANGE su700 input.transfer.low

#### CLIENT

Form:

    LIST CLIENT <device_name>
    LIST CLIENT ups1

Response:

    BEGIN LIST CLIENT <device_name>
    CLIENT <device name> <client IP address>
    ...
    END LIST CLIENT <device_name>

    BEGIN LIST CLIENT ups1
    CLIENT ups1 ::1
    CLIENT ups1 192.168.1.2
    END LIST CLIENT ups1

See also `GET NUMLOGINS <upsname>` to get just the count of connected clients.

### 10.6. SET

#### VAR

Form:

    SET VAR <upsname> <varname> "<value>"
    SET VAR su700 ups.id "My UPS"

Response:

    OK                         (if TRACKING is not enabled)
    OK TRACKING <id>           (if TRACKING is enabled)
    ERR <message> [<extra>...] (see Error responses)

#### TRACKING

Form:

    SET TRACKING <value>
    SET TRACKING ON
    SET TRACKING OFF

Response:

    OK
    ERR INVALID-ARGUMENT  (if <value> is not "ON" or "OFF")
    ERR USERNAME-REQUIRED (if not yet authenticated)
    ERR PASSWORD-REQUIRED (if not yet authenticated)

### 10.7. INSTCMD

Form:

    INSTCMD <upsname> <cmdname> [<cmdparam>]
    INSTCMD su700 test.panel.start
    INSTCMD su700 load.off.delay 120

### Note

<cmdparam> is an additional and optional parameter for the command.

Response:

    OK                         (if TRACKING is not enabled)
    OK TRACKING <id>           (if TRACKING is enabled)
    ERR <message> [<extra>...] (see Error responses)

### 10.8. LOGOUT

Form:

    LOGOUT

Response:

    OK Goodbye      (recent versions)
    Goodbye...      (older versions)

Used to disconnect gracefully from the server.

### 10.9. LOGIN

Form:

    LOGIN <upsname>

Response:

    OK      (upon success)

or various errors

### Note

This requires "upsmon secondary" or "upsmon primary" in upsd.users

Use this to log the fact that a system is drawing power from this UPS. The upsmon primary will wait until the count of attached systems reaches 1 — itself. This allows the secondaries to shut down first.

### Note

You probably shouldn’t send this command unless you are upsmon, or a upsmon replacement.

### 10.10. PRIMARY (since NUT 2.8.0) or MASTER (deprecated)

### Note

This command was renamed in NUT 2.8.0 to "PRIMARY" with the older name "MASTER" kept as deprecated alias for compatibility.

Form:

    MASTER <upsname>

Response:

    OK MASTER-GRANTED       (upon success)

Form:

    PRIMARY <upsname>

Response:

    OK PRIMARY-GRANTED      (upon success)

or various errors

### Note

This requires "upsmon primary" in upsd.users

### Note

Previously documented response was just `OK`— clients checking that server reply starts with that keyword would handle all cases.

This function doesn’t do much by itself. It is used by upsmon to make sure that primary-mode functions like FSD are available if necessary.

### 10.11. FSD

Form:

    FSD <upsname>

Response:

    OK FSD-SET      (success)

or various errors

### Note

This requires "upsmon primary" in upsd.users, or "FSD" action granted in upsd.users

upsmon in primary mode is the primary user of this function. It sets this "forced shutdown" flag on any UPS when it plans to power it off. This is done so that secondary systems will know about it and shut down before the power disappears.

Setting this flag makes "FSD" appear in a STATUS request for this UPS. Finding "FSD" in a status request should be treated just like a "OB LB".

It should be noted that FSD is currently a latch — once set, there is no way to clear it short of restarting upsd or dropping then re-adding it in the ups.conf. This may cause issues when upsd is running on a system that is not shut down due to the UPS event.

Note also that certain drivers can propagate the "FSD" state declared by the smarter UPSes themselves, e.g. when an UPS is charging after an outage and its battery level is below the "safe for load" threshold configured on the device itself. In this case the device usually does not power up its outlets automatically, but it can be forced by the systems administrator. The rationale behind such FSD during charging allows enough power to be guaranteed for systems to both boot and shut down safely, if the wall power disappears again, trading off prolonged unavailability of the shut down servers for the safety of their data. In such cases, administrators should be ready to disarm their upsmon clients until the batteries are charged, to avoid quick shutdowns of quickly restored servers — but only if they are sure about the wall power being restored for good (e.g. outage was due to maintenance).

### 10.12. PASSWORD

Form:

    PASSWORD <password>

Response:

    OK      (upon success)

or various errors

Sets the password associated with a connection. Used for later authentication for commands that require it.

### 10.13. USERNAME

Form:

    USERNAME <username>

Response:

    OK      (upon success)

or various errors

Sets the username associated with a connection. This is also used for authentication, specifically in conjunction with the upsd.users file.

### 10.14. STARTTLS

Form:

    STARTTLS

Response:

    OK STARTTLS

or various errors

This tells upsd to switch to TLS mode internally, so all future communications will be encrypted. You must also change to TLS mode in the client after receiving the OK, or the connection will be useless.

### 10.15. Other commands

- HELP: lists the commands supported by this server
- VER: shows the version of the server currently in use
- NETVER: shows the version of the network protocol currently in use (aliased as PROTVER since NUT v2.8.0, or formal protocol version 1.3)

These three are not intended to be used directly by programs. Humans can make use of this program by using telnet or netcat. If you use telnet, make sure you don’t have it set to negotiate extra options. upsd doesn’t speak telnet and will probably misunderstand your first request due to the extra junk in the buffer.

### 10.16. Error responses

An error response has the following format:

    ERR <message> [<extra>...]

<message> is always one element; it never contains spaces. This may be used to allow additional information (<extra>) in the future.

<message> can have the following values:

- ACCESS-DENIED

  The client’s host and/or authentication details (username, password) are not sufficient to execute the requested command.

- UNKNOWN-UPS

  The UPS specified in the request is not known to upsd. This usually means that it didn’t match anything in ups.conf.

- VAR-NOT-SUPPORTED

  The specified UPS doesn’t support the variable in the request.

  This is also sent for unrecognized variables which are in a space which is handled by upsd, such as server.*.

- CMD-NOT-SUPPORTED

  The specified UPS doesn’t support the instant command in the request.

- INVALID-ARGUMENT

  The client sent an argument to a command which is not recognized or is otherwise invalid in this context. This is typically caused by sending a valid command like GET with an invalid subcommand.

- INSTCMD-FAILED

  upsd failed to deliver the instant command request to the driver. No further information is available to the client. This typically indicates a dead or broken driver.

- SET-FAILED

  upsd failed to deliver the set request to the driver. This is just like INSTCMD-FAILED above.

- READONLY

  The requested variable in a SET command is not writable.

- TOO-LONG

  The requested value in a SET command is too long.

- FEATURE-NOT-SUPPORTED

  This instance of upsd does not support the requested feature. This is only used for TLS/SSL mode (STARTTLS) at the moment.

- FEATURE-NOT-CONFIGURED

  This instance of upsd hasn’t been configured properly to allow the requested feature to operate. This is also limited to STARTTLS for now.

- ALREADY-SSL-MODE

  TLS/SSL mode is already enabled on this connection, so upsd can’t start it again.

- DRIVER-NOT-CONNECTED

  upsd can’t perform the requested command, since the driver for that UPS is not connected. This usually means that the driver is not running, or if it is, the ups.conf is misconfigured.

- DATA-STALE

  upsd is connected to the driver for the UPS, but that driver isn’t providing regular updates or has specifically marked the data as stale. upsd refuses to provide variables on stale units to avoid false readings.

  This generally means that the driver is running, but it has lost communications with the hardware. Check the physical connection to the equipment.

- ALREADY-LOGGED-IN

  The client already sent LOGIN for a UPS and can’t do it again. There is presently a limit of one LOGIN record per connection.

- INVALID-PASSWORD

  The client sent an invalid PASSWORD — perhaps an empty one.

- ALREADY-SET-PASSWORD

  The client already set a PASSWORD and can’t set another. This also should never happen with normal NUT clients.

- INVALID-USERNAME

  The client sent an invalid USERNAME.

- ALREADY-SET-USERNAME

  The client has already set a USERNAME, and can’t set another. This should never happen with normal NUT clients.

- USERNAME-REQUIRED

  The requested command requires a username for authentication, but the client hasn’t set one.

- PASSWORD-REQUIRED

  The requested command requires a passname for authentication, but the client hasn’t set one.

- UNKNOWN-COMMAND

  upsd doesn’t recognize the requested command.

  This can be useful for backwards compatibility with older versions of upsd. Some NUT clients will try GET and fall back on REQ after receiving this response.

- INVALID-VALUE

  The value specified in the request is not valid. This usually applies to a SET of an ENUM type which is using a value which is not in the list of allowed values.

### 10.17. Future ideas

#### Dense lists

The LIST commands may be given the ability to handle options some day. For example, `LIST VARS <ups> +DESC` would return the current value like now, but it would also append the description of that variable.

#### Logout pending

Add a way for logged-in clients such as upsmon(8) to tell the data server that they began their shutdown routine, so eventual loss of connection would be quickly interpreted as a `LOGOUT` (without any wait for further timeouts, as a usual disconnection may be treated).

This is useful in context of PR #3086 where clients can configure `SHUTDOWNEXIT` behavior to NOT end the program (and log out) as soon as they tell the OS to shut down, but rather stay in a heart-beat loop to tell the data server that they are still alive (for specified time or indefinitely, until the OS cuts power or networking maybe before it ends the client process), as a way to delay the primary client proceeding with its shutdown and cutting the UPS power until some important secondary clients are actually safely "parked".

#### Get collection

Allow to request only a subtree, which can be a collection, or a sub collection.

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