Section: Hamlib Utilities (1)
Updated: 2019-12-10
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ampctld - TCP amplifier control daemon  


[ -hlLuV ] [ -m id ] [ -r device ] [ -s baud ] [ -T IPADDR ] [ -t number ] [ -C parm=val ] [-v[-Z]]  


The ampctld program is an amplifier control daemon that handles client requests via TCP sockets. This allows multiple user programs to share one amplifier (this needs more development). Multiple amplifiers can be controlled on different TCP ports by use of multiple ampctld processes. Note that multiple processes/ports are also necessary if some clients use extended responses and/or vfo mode. So up to 4 processes/ports may be needed for each combination of extended response/vfo mode. The syntax of the commands are the same as ampctl(1). It is hoped that ampctld will be especially useful for client authors using languages such as Perl, Python, PHP, and others.

ampctld communicates to a client through a TCP socket using text commands shared with ampctl. The protocol is simple, commands are sent to ampctld on one line and ampctld responds to get commands with the requested values, one per line, when successful, otherwise, it responds with one line "RPRT x", where 'x' is a negative number indicating the error code. Commands that do not return values respond with the line "RPRT x", where 'x' is '0' when successful, otherwise is a regative number indicating the error code. Each line is terminated with a newline '\n' character. This protocol is primarily for use by the NET ampctl (amplifier model 2) backend.

A separate Extended Response Protocol extends the above behavior by echoing the received command string as a header, any returned values as a key: value pair, and the "RPRT x" string as the end of response marker which includes the Hamlib success or failure value. See the PROTOCOL section for details. Consider using this protocol for clients that will interact with ampctld directly through a TCP socket.

Keep in mind that Hamlib is BETA level software. While a lot of backend libraries lack complete amplifier support, the basic functions are usually well supported.

Please report bugs and provide feedback at the e-mail address given in the BUGS section below. Patches and code enhancements sent to the same address are welcome.  


This program follows the usual GNU command line syntax. Short options that take an argument may have the value follow immediately or be separated by a space. Long options starting with two dashes ('-') require an '=' between the option and any argument.

Here is a summary of the supported options:

-m, --model=id
Select amplifier model number.
See model list (use "ampctl -l").
Note: ampctl (or third party software using the C API) will use amplifier model 2 for NET ampctl (communicating with ampctld).
-r, --amp-file=device
Use device as the file name of the port connected to the amplifier.
Often a serial port, but could be a USB to serial adapter. Typically /dev/ttyS0, /dev/ttyS1, /dev/ttyUSB0, etc. on Linux, COM1, COM2, etc. on MS Windows. The BSD flavors and Mac OS/X have their own designations. See your system's documentation.
-s, --serial-speed=baud
Set serial speed to baud rate.
Uses maximum serial speed from amplifier backend capabilities (set by -m above) as the default.
-t, --port=number
Use number as the TCP listening port.
The default is 4531.
Note: As rigctld's default port is 4532 and rotctld's default port is 4533, it is recommended to use DESCENDING odd numbered ports for multiple ampctld instances, e.g. 4529, 4527, 4525, etc.
-T, --listen-addr=IPADDR
Use IPADDR as the listening IP address.
The default is ANY.
-L, --show-conf
List all config parameters for the amplifier defined with -m above.
-C, --set-conf=parm=val[,parm=val]
Set amplifier configuration parameter(s), e.g. stop_bits=2.
Use the -L option above for a list of configuration parameters for a given model number.
-u, --dump-caps
Dump capabilities for the amplifier defined with -m above and exit.
-l, --list
List all amplifier model numbers defined in Hamlib and exit.
The list is sorted by model number.
Note: In Linux the list can be scrolled back using Shift-PageUp/Shift-PageDown, or using the scrollbars of a virtual terminal in X or the cmd window in Windows. The output can be piped to more(1) or less(1), e.g. "ampctl -l | more".
-v, --verbose
Set verbose mode, cumulative (see DIAGNOSTICS below).
-Z, --debug-time-stamps
Enable time stamps for the debug messages.
Use only in combination with the -v option as it generates no output on its own.
-h, --help
Show a summary of these options and exit.
-V, --version
Show version of ampctl and exit.

Note: Some options may not be implemented by a given backend and will return an error. This is most likely to occur with the --set-conf and --show-conf options.

Please note that the backend for the amplifier to be controlled, or the amplifier itself may not support some commands. In that case, the operation will fail with a Hamlib error code.  


Commands can be sent over the TCP socket either as a single char, or as a long command name plus the value(s) space separated on one '\n' terminated line. See PROTOCOL.

Since most of the Hamlib operations have a set and a get method, an upper case letter will be used for set methods whereas the corresponding lower case letter refers to the get method. Each operation also has a long name; prepend a backslash, '\', to send a long command name.

Example (Perl): "print $socket "\\dump_caps\n";" to see what the amplifier's backend can do (Note: In Perl and many other languages a '\' will need to be escaped with a preceding '\' so that even though two backslash characters appear in the code, only one will be passed to ampctld. This is a possible bug, beware!).

Note: The backend for the amplifier to be controlled, or the amplifier itself may not support some commands. In that case, the operation will fail with a Hamlib error message.

Here is a summary of the supported commands (In the case of set commands the quoted italicized string is replaced by the value in the description. In the case of get commands the quoted italicized string is the key name of the value returned.):

F, set_freq 'Frequency'
Set 'Frequency', in Hz.
Frequency may be a floating point or integer value.
f, get_freq
Get 'Frequency', in Hz.
Returns an integer value.
l, get_level 'Level'
Get 'Level Value'.
Returns Level Value as a float or integer for the Level token given.
Note: Passing a '?' (query) as the first argument instead of a Level token will return a space separated list of amplifier backend supported get level tokens. Use this to determine the supported levels of a given amplifier backend.
Return certain state information about the amplifier backend.
1, dump_caps
Not a real amplifier remote command, it just dumps capabilities, i.e. what the backend knows about this model, and what it can do.
TODO: Ensure this is in a consistent format so it can be read into a hash, dictionary, etc. Bug reports requested.
Note: This command will produce many lines of output so be very careful if using a fixed length array! For example, running this command against the Dummy backend results in a number of lines of text output.
_, get_info
Return information from the amplifier backend.
R, reset 'Reset'
Perform amplifier 'Reset'.
Reset is an integer value: '0' = None, '1' = Memory reset, '2' = Fault reset, '3' = Amplifier reset.
set_powerstat 'Power Status'
Set 'Power Status'.
Power Status is an integer value: '0' = Power Off, '1' = Power On, '2' = Power Standby (enter standby), '4' = Power Operate (leave standby).
Get 'Power Status' as in set_powerstat above.


There are two protocols in use by ampctld, the Default Protocol and the Extended Response Protocol.

The Default Protocol is intended primarily for the communication between Hamlib library functions and ampctld ("NET ampctl", available using amplifier model '2').

The Extended Response Protocol is intended to be used with scripts or other programs interacting directly with ampctld as consistent feedback is provided.  

Default Protocol

The Default Protocol is intentionally simple. Commands are entered on a single line with any needed values. In practice, reliable results are obtained by terminating each command string with a newline character, '\n'.

Example set frequency and mode commands (Perl code):

print $socket "F 14250000\n";
print $socket "\\set_powerstat 1\n"; # escape leading '\'

A one line response will be sent as a reply to set commands, "RPRT x\n" where x is the Hamlib error code with '0' indicating success of the command.

Responses from ampctld get commands are text values and match the same tokens used in the set commands. Each value is returned on its own line. On error the string "RPRT x\n" is returned where x is the Hamlib error code.

Example get frequency (Perl code):

print $socket "f\n";

Most get functions return one to three values. A notable exception is the dump_caps command which returns many lines of key:value pairs.

This protocol is primarily used by the "NET ampctl" (ampctl model 2) backend which allows applications already written for Hamlib's C API to take advantage of ampctld without the need of rewriting application code. An application's user can select amplifier model 2 ("NET ampctl") and then set amp_pathname to "localhost:4531" or other network host:port (set by the -T/-t options, respectively, above).  

Extended Response Protocol

The Extended Response protocol adds several rules to the strings returned by ampctld and adds a rule for the command syntax.

1. The command received by ampctld is echoed with its long command name followed by the value(s) (if any) received from the client terminated by the specified response separator as the first record of the response.

2. The last record of each block is the string "RPRT x\n" where x is the numeric return value of the Hamlib backend function that was called by the command.

3. Any records consisting of data values returned by the amplifier backend are prepended by a string immediately followed by a colon then a space and then the value terminated by the response separator. e.g. "Frequency: 14250000\n" when the command was prepended by '+'.

4. All commands received will be acknowledged by ampctld
 with records from rules 1 and 2.  Records from rule 3 are only returned when data values must be returned to the client.

4. All commands received will be acknowledged by ampctld with records from rules 1 and 2. Records from rule 3 are only returned when data values must be returned to the client.

An example response to a set_frequency command sent from the shell prompt (note the prepended '+'):

$ echo "+F 14250000" | nc -w 1 localhost 4531
set_freq: 14250000

In this case the long command name and values are returned on the first line and the second line contains the end of block marker and the numeric amplifier backend return value indicating success.

An example response to a get_freq query:

$ echo "+\get_freq" | nc -w 1 localhost 4531
Frequency(Hz): 14250000
Note: The '\' is still required for the long command name even with the ERP character.

In this case, as no value is passed to ampctld, the first line consists only of the long command name. The final line shows that the command was processed successfully by the amplifier backend.

Invoking the Extended Response Protocol requires prepending a command with a punctuation character. As shown in the examples above, prepending a '+' character to the command results in the responses being separated by a newline character ('\n'). Any other punctuation character recognized by the C ispunct() function except '\', '?', or '_' will cause that character to become the response separator and the entire response will be on one line.

Separator character summary:

Each record of the response is appended with a newline ('\n').
';', '|', or, ','
Each record of the response is appended by the given character resulting in entire response on one line.
These are common record separators for text representations of spreadsheet data, etc.
Reserved for help in ampctl.
Reserved for get_info short command
Reserved for comments when reading a command file script.
Note: Other punctuation characters have not been tested! Use at your own risk.

For example, invoking a get_freq query with a leading ';' returns:

get_freq:;Frequency(Hz): 14250000;RPRT 0

Or, using the pipe character '|' returns:

get_freq:|Frequency(Hz): 14250000|RPRT 0

And a set_freq command prepended with a '|' returns:

set_freq: 14250000|RPRT 0

Such a format will allow reading a response as a single event using a preferred response separator. Other punctuation characters have not been tested!  


The -v, --verbose option allows different levels of diagnostics to be output to stderr and correspond to -v for BUG, -vv for ERR, -vvv for WARN, -vvvv for VERBOSE, or -vvvvv for TRACE.

A given verbose level is useful for providing needed debugging information to the email address below. For example, TRACE output shows all of the values sent to and received from the amplifier which is very useful for amplifier backend library development and may be requested by the developers.  


Start ampctld for an Elecraft KPA-1500 using a USB-to-serial adapter and backgrounding:

$ ampctld -m 201 -r /dev/ttyUSB1 &

Start ampctld for an Elecraft KPA-1500 using COM2 on MS Windows:

$ ampctld -m 201 -r COM2

Connect to the already running ampctld and set the frequency to 14.266 MHz with a 1 second read timeout using the default protocol from the shell prompt:

$ echo "\set_freq 14266000" | nc -w 1 localhost 4531

Connect to a running ampctld with ampctl on the local host:

$ ampctl -m2


No authentication whatsoever; DO NOT leave this TCP port open wide to the Internet. Please ask if stronger security is needed or consider using a Secure Shell (ssh(1)) tunnel.

As ampctld does not need any greater permissions than ampctl, it is advisable to not start ampctld as "root" or another system user account in order to limit any vulnerability.  


The daemon is not detaching and backgrounding itself.

No method to exit the daemon so the kill(1) command must be used to terminate it.

Multiple clients using the daemon may experience contention with the connected amplifier.

Report bugs to:

Hamlib Developer mailing list


This file is part of Hamlib, a project to develop a library that simplifies radio, rotator, and amplifier control functions for developers of software primarily of interest to radio amateurs and those interested in radio communications.

Copyright © 2000-2010 Stephane Fillod
Copyright © 2000-2018 the Hamlib Group (various contributors)
Copyright © 2011-2019 Nate Bargmann

This is free software; see the file COPYING for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  


kill(1), ampctl(1), ssh(1), hamlib(7)  


Links to the Hamlib Wiki, Git repository, release archives, and daily snapshot archives:



Default Protocol
Extended Response Protocol
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