On Thu, Jul 31, 2025 at 08:45:19 -0400, Dan Purgert wrote: > On Jul 31, 2025, mick.crane wrote: > > I assumed a serial console was a device with a screen and keyboard. > > If you're thinking of things like the VT-100; I believe that the > physical device would be referred to as a "Terminal" (which would then > allow you to access the machine Console). > > It's pretty fuzzy though -- since if "console" means "user interface", > then the VT-100 (being a physical manifestation of "user interface") is > a console. Not 100% sure what makes the distinction there.
I think the term "serial console" came into vogue around the time Linux and the BSDs started to be used on personal computers. On a typical PC running Linux, the "console" (main administrative command-line interface) is usually accessed via a directly attached keyboard and monitor. The keyboard may be attached via a PS2 port, or a USB port, while the monitor was originally VGA, and nowadays may also be HDMI or DisplayPort. Administratively, the console often has special privileges. It shows messages during system boot, and it may receive additional kernel messages that are not sent to other terminals. Sometimes, direct root logins are permitted only on the console, and not on other terminals. On Linux systems, it's common for "startx" to be allowed only on the console, and not on other terminals, even if those other terminals are capable of graphics. A "serial console", then, is an alternative means of accessing the system console, via a serial port, instead of some combination of directly attached "PC-ish" hardware. A terminal attached to the serial port would communicate at a much lower data rate (typically 9600 baud in the early days, probably faster on most modern hardware). For context, at 9600 baud, most people can see the characters being displayed in real time. It takes a noticeable amount of time for a screen full of text to be received and rendered. A true, full-featured serial console would ideally display messages while the system is booting, which requires some kernel support, as those messages are usually displayed on the VGA/HDMI/DP monitor. In a data center context, a server with a serial console might be one of several such devices, which all have their serial ports connected to some sort of central monitoring system, which can record their serial console messages, and offer remote login access over said serial ports for administration.
