In these modern times, the hardworking admin might be tempted to turn her back on the Old Ways and indulge in increasingly exotic methods of interfacing with servers: Ethernet, USB, Firewire, Wireless, Infrared, KVM switches—next stop: direct neural implants.
There is one old-timer that still has a useful place in the network admininstrator’s toolkit: the serial console. It’s simple and cheap—you don’t need to install drivers or expansion cards, it’s just there. It’s the lowest-level means of interfacing with your system. Configure your servers to accept serial logins, set up a laptop as a portable console, and you have an instant cheap rescue device when everything else fails.
Your portable serial console will also serve you well when you need it to connect to routers and switches.
When you’re troubleshooting headless systems, it saves the hassle of hooking up a keyboard and monitor. You can capture kernel and logging messages that otherwise would be lost, reboot the system and get a boot menu, edit network settings and stop/start networking, restart or tweak SSH, and tweak network card settings.
I don’t recommend it as your sole means of server administration—Ethernet is a lot faster. But, when nothing else works, the serial console will save the day.
There are a number of ways to make the physical connection. You can connect a hardware-controller modem, the kind old-timers fondly refer to as real modems, ...