What is it?
The tncattach utility is a small and portable utility for attaching KISS TNCs as network interfaces in Linux. It is intended to replace functionality from the kissattach program. With tncattach you can bring up a full ethernet interface with a TNC by simply issuing:
sudo tncattach /dev/ttyUSB0 115200 --ethernet
The program supports various options, and allows you to create either full ethernet devices, suitable for point-to-multipoint setups, or more simple point-to-point interfaces. For more information, downloads and usage examples, please read the current instructions on the tncattach GitHub page.
Why replace the kissattach utility?
In many newer distributions, specifically all those based on Debian Buster, which includes popular operating systems such as Ubuntu and Raspbian, the kissattach utility is no longer functioning correctly, and in many cases simply stops working all together.
In addition, the AX.25 Linux kernel support, that kissattach and similar utilities rely on, is unfortunately in a more or less unmaintained state, and removal is being considered by the package maintainers.
If kernel AX.25 support is removed, it would mean very limited options for using TNCs on Linux, and it is the intention to continue supplying those options in a more modern, portable and maintainable way with the tncattach utility.