SAC - Serial Access Concentrator

This project makes a number of devices that have a serial console port for management available over the network. Examples are network switch management ports, server management ports such as iLO or ILOM, SGI L1, etc. I like the Opengear CM7100 Console Servers. This is a budget alternative.

General info
Requirements
Setup

General Info

This is a script that acts as a serial access concentrator, i.e. it makes a number of local serial ports accessible via SSH. It leverages on-board technologies, such as SSH for secure access and udev for device management.

Besides port 22 the SSH daemon is configured to also listen on port 4000 and above. The user logs in, and depending on the port the user selected the script selects a serial port.

This will connect to the first serial port

ssh -p4000 user@host

This will connect to the second serial port

ssh -p4001 user@host

And so on, while this will connect to a regular shell

ssh user@host

On successful login, a hook in the user's .bashrc (or equivalent) will call a script. The script checks if the login originated from an SSH session. If true, it will evaluate the incoming TCP port of that session. It will look up the TCP port in a configuration file. If the script finds a mapped serial port for the incoming TCP port, it will open a screen session, otherwise it will exit.

The mapping of TCP port to serial port, along with baudrate and a comment, is stored in a configuration file: serialports.json

	{
			"port": "4000",
			"device": "/dev/ttySLAB0",
			"baudrate": "115200",
			"comment": "#A9J7NQ5D Server iLO management interface"
	},
	{
			"port": "4001",
			"device": "/dev/ttySLAB1",
			"baudrate": "115200",
			"comment": "#AL02JQ1T Switch management interface"
	},

Requirements

jq - Command-line JSON processor
If you're using USB-serial cables, I recommend getting those an FTDI chip, because these have a serial numbers. The serial number makes it possible to uniquely identify a USB-serial cable and further the device that is attached to it.

Setup

Deploy source

Clone this repository into the user's home directory, i.e. ~/sac.

Configure SSH Daemon

Configure the SSH Daemon to listen on more ports. Edit /etc/sshd/sshd_config and add a number of ports like so:

Port 22
Port 4000
Port 4001
Port 4002
Port 4003
Port 4004
Port 4005
Port 4006

Configure udev

The udev daemon helps getting a static mapping between selected TCP port and device we're trying to connect to. When using USB-serial cables we use the serial number of each cable to identify it across reboots.

SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A9J7NQ5D", SYMLINK+="ttySLAB0"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="AL02JQ1T", SYMLINK+="ttySLAB1"

Edit ~/sac/70-serial-port.rules to adapt the serial numbers to match your cables.
Copy the file ~/sac/70-serial-port.rules to /etc/udev/rules.d/
Restart the udev daemon.

Hint: You will find the serial number of your USB-serial cables in dmesg. On plug-in, the drivers will print a message like this:

[    2.006449] usb 3-1.7: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
[    2.006454] usb 3-1.7: Product: FT232R USB UART
[    2.006455] usb 3-1.7: Manufacturer: FTDI
[    2.006457] usb 3-1.7: SerialNumber: A9P977MW

I like to mark my cables with the serial number, so I can map the device I plug them into.

Edit your serial port configuration

Edit ~/sac/serialports.json. Configure the port, baudrate, and comment pointing to the device the serial port is connected to (e.g. server iLO, switch management port, SGI L1, etc.)

Add hook to bashrc

Add a call to ~/sac/connect.sh to the beginning of ~/.bashrc (or equivalent), e.g.

# If not running interactively, don't do anything
case $- in
    *i*) ;;
      *) return;;
esac

. ~/sac/connect.sh

Connect

Connect via SSH to your device's serial port:

ssh -p4000 user@host

skytee / sac