Serial over SSH

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The Serial over SSH plugin extends the power and simplicity of IO Ninja’s Serial plugin to remote Linux devices, enabling control of serial ports on machines like headless Raspberry Pi boards.

Basic Setup

Prerequisites

Enabling SSH

On most Linux machines, SSH is enabled by default. However, if it is not, you will need to enable it.

On Raspbian and many other popular distros, you can perform the following command:

systemctl enable --now sshd

For other Linux distributions, please refer to their documentation.

Installing the Hardware Client

The Serial over SSH plugin uses the IO Ninja Hardware Client (ioninja-hwc).

This hardware client needs to be installed and configured on the remote machine.

See Installing the Hardware Client for instructions.

Identifying the Port

Later on, you will need to know what port your serial device is connected to.

On your Linux machine, perform the following command:

ioninja-hwc --ser-enum

The terminal should print all discovered ports, and you should see your serial device, similar to this:

/dev/ttyUSB0

This string of text will be entered into IO Ninja later, so make a note of it.

Alternatively, you can perform the following command:

dmesg --follow | grep -i tty

While the process is running, reconnect your device.

The terminal should print a new line, similar to this:

usb 1‑1.1: FIDI USB Serial Device converter now attached to ttyUSB0

In this case, the output indicates the port used is ttyUSB0, but yours may be different.

Serial SSH’ing into your Linux Machine with IO Ninja

In IO Ninja, click the “New Session” dropdown and select a new “Serial over SSH” session.

Type the host address of your remote Linux machine into the “Address:” field.

Type the port we identified earlier into the “Port:” field, prefixed by /dev/.

Click the “Open” button to the right of the “Port:” field to initiate a connection.

You will be prompted for SSH credentials.

Adjust settings as needed via the “Settings” button (see “Settings” section below for details).

Many of these settings are also available in the “Control” pane for easy access.

Communicate with your Serial Device as Usual

In the “Transmit” pane, type your binary packet and press “Send”.

See all communications in the Ninja Scroll Engine.

Add a layer such as Modbus Analyzer to make the most out of Modbus communications.

Settings

Setting	Description	Default
Remote address	Remote address to connect to. Can be specified via IPv4 (`127.0.0.1`), IPv6 (`::1`), or a domain name (`localhost`). Remote address can be suffixed with the remote port after a colon, e.g. `ioninja.com:443`.
Remote port (default)	Remote port to connect to in cases when a port is not explicitly specified in Remote address.	80
Use local address	Bind socket to the specified local address.	False
Adapter	Local network adapter to bind to. Pick one from the list of installed network adapters (or bind to all installed `IP4` or all `IP6` adapters at once).	Auto
Local port	Local port to bind to. Setting this to `0` auto-selects an available port.	8080
Reuse address	Allow multiple sockets to share the same local address. Maps to the `SO_REUSEADDR` socket option. Please note, the support and details of implementation for this option are highly platform-specific.	False
TCP Nagle algorithm	Delay transmission to reduce the number of small TCP packets. Maps to the `TCP_NODELAY` socket option.	False
TCP reset	Drop TCP connections abruptly with a TCP RST packet. Maps to the `SO_LINGER` socket option.	False
TCP keep-alives	Detect connection loss with TCP keep-alive probes. Maps to the `TCP_KEEPALIVE` socket option.	False
User name	User name for SSH authentication.
User authentication	SSH authentication method (password or private key)	Password
Private key file	Private key file for SSH authentication (PEM format).
Remember last password	Re-use the last entered password during subsequent connect attempts.	True
Port	The port that should be used.
Baud rate	The serial baud rate.	38400 bps
Data bits	Serial data bit count (word size). See available options.	8 bits
Parity	Serial parity check type. See available options.	None
Stop bits	Serial stop bit count. See available options.	1 bit
Flow control	Serial flow control. See available options.	None
DTR	State of the DTR (Data-Terminal-Ready) modem control line.	True
RTS	State of the RTS (Request-to-Send) modem control line.	False
BREAK	Enable the BREAK condition on the TX line.	False
Read block size (B)	The size of each individual read block submitted to the underlying transport.	4KB
RX buffer size (B)	The full size of the incoming data (RX) buffer. Affects read throughput.	16KB
TX buffer size (B)	The full size of the outbound data (TX) buffer. Affects write throughput..	16KB
Keep read block size	Don’t merge read blocks in RX buffer. Incoming data blocks coming in quick succession can be merged together so that IO Ninja writes them to log as a whole. When this option is set to `True`, blocks are written to the log without merging, i.e., exactly as they are received from the underlying transport..	False
Keep write block size	Don’t merge write blocks in TX buffer. Outbound data blocks sent in quick succession can be merged together before submission to the underlying transport. When this option is set to `True`, blocks are submitted to the transport without merging, i.e., exactly as they are sent by the Transmit or Script panes..	False
RX buffer full notifications	Toggle warnings in log about the incoming data (RX) buffer getting full.	False
Serial setting changes	Toggle notifications about serial setting (baud rate, data size, parity, stop bits, flow control) changes in the log.	on
DTR/RTS changes	Toggle notifications about control line (`DTR`, `RTS`) changes in the log.	on
DSR/CTS/DCD/RI changes	Toggle notifications about status line (`DSR`, `CTS`, `DCD`, `RI`) changes in the log.	on
Serial line errors	Toggle warning about serial line errors (`PARITY`, `FRAMING` and `BREAK`) in the log.	on

Data Bit Options

Option
5 bits
6 bits
7 bits
8 bits

Parity Options

Option	Description
None	No parity bit is used
Odd	Odd parity (parity bit is set when the number of logical ones in the UART frame is odd).
Even	Even parity (parity bit is set when the number of logical ones in the UART frame is even).
Mark	Parity bit is present and always set.
Space	Parity bit is present and always clear.

Stop Bit Options

Option
1 bit
1.5 bits
2 bits

Flow Control Options

Option	Description
None	No flow control.
RTS/CTS	Hardware flow control using CTS and RTS lines.
XON/XOFF	Software flow control using XON and XOFF lines.

FAQ (Frequently Asked Questions)

1. How can I automatically append line ending characters?

Appending line ending characters is easily achieved using the TX Modifier Layer plugin.

To automatically append line endings:

Add the TX Modifier layer to your serial session.
In the layer settings, enable the Append suffix option.
Enter the desired suffix (e.g., \r\n) in the configuration.

This will automatically add your specified line endings to all outgoing transmissions—saving you from typing them manually each time. The TX Modifier layer also supports many other advanced transformations, but you can keep it simple if you only need suffixes.

2. Can I timestamp each line of serial data based on carriage return (CR) rather than fixed-size blocks, and export it for use in external software?

IO Ninja timestamps entire data blocks as they are received from the operating system, not individual bytes. Since bytes within a block arrive in quick succession, the block timestamp provides a reliable indication of when the data was received. Although you cannot assign timestamps to each CR-terminated line directly, the existing timestamps offer millisecond-level accuracy and can be exported for use in test or simulation systems.