East of the Sun, West of the Moon

2007/9/26

Old tech, new tech

Filed under: Software,Technology — Erwin @ 12:56 pm

Serial consoles are older tech than most people reading this blog, I suspect, but with USB being thrown in the mix you can do some interesting things, like connecting the serial port of several servers via an equal amount of USB-to-serial adapters to a single USB hub which then hooks up to the poor man’s version of a remote serial console server, using /dev/ttyUSB0, /dev/ttyUSB1, etc instead of /dev/ttyS0, /dev/ttyS1, etc to connect to the various consoles.

I have to admit I hadn’t worked with serial consoles before. That is to say I’d used them when someone else had already set them up, at a previous job, but I hadn’t set up a Linux boot loader or kernel to make use of one, so I had some fun with that yesterday.

Notes to self:

  • Make sure the speed settings in /etc/inittab and /etc/lilo.conf are the same or you’ll have some fun line noise to admire.
  • The USB Serial Converter I picked up worked out of the box with the Linux 2.6.18 kernel I’m running. That’s worth noting because things aren’t always quite so agreeable.
  • Null-modems come in very different shapes and sizes. There’s the ultra-small mini null modem adaptor for just $2.00 and of course the usual 6 to 10 ft null modem cables. It depends on the circumstances what suits your needs the most.
  • Because it seems to be a bit of a pain to send the break signal to the serial console when you’re connecting via ssh via telnet to the actual serial cable, it helps to configure LILO such that you don’t need to. I use these settings:
      prompt
      timeout=100
      delay=100
      serial=0,9600n8
      append="console=tty0 console=ttyS0,9600"
    

    The first three lines make sure I get a “boot:” prompt but proceed with regular boot after 10 seconds. The last two lines cause the LILO and kernel output to be visible on both serial and regular console.

The other thing I played with recently was some USB-ethernet adapters. For future reference, out of the box the TRENDnet TU2-ET100 worked with Linux 2.6.18 (using the “asix” module), while the D-Link DUB-E100 and Startech USB2105S did not! For those last two I had gotten the impression that they could work, but no luck. There’s a good chance that the D-Link changed chipsets without changing its name, an unfortunately not unusual behaviour in the business. I suspect that with some custom kernel compiling I could’ve gotten the Startech device to work, but I am trying to avoid that at the moment, not wanting extra work when it is time to upgrade to a more recent kernel.

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