Monday, December 8, 2014

Linux floppy based serial terminal.

Last article I talked about using a dos disk to access some terminal software. Here is a disk that is allegedly pure linux to act as a terminal. It seemed to work on the old 486 laptop connected to the arch linux based pogoplug, though I did not check it out completely.

PiTuX is a floppy based Linux distro that turns an old, low-RAM, machine in a very useful serial terminal running minicom. Think about your old laptop as a pure VT102.
  • PiTuX boots from a floppy and runs completely in ram so you can even have a diskless PC.
  • New: persistent configuration! Configure minicom as you need and if you want you can have config files stored and saved over reboots.
  • It works from 386, without math coprocessor, up and NEEDS ONLY 4 MB RAM.
  • It doesn't have any kind of support for hard disks so it will not mess up data on them
  • Most 386 and 486 can run even without a fan so you can have a very silent serial terminal at the prize of a NULL MODEM cable.
  • 2.4 recent kernel, lightweight uClibc, and real minicom 2.1
  • full color, full ANSI mode!
for administration of headless Linux/*BSD/VAX/etc, multiple servers/PC without the need of a KVM switch, installations via serial console, modem/router/firewall setup, monitoring equipment, embedded systems development, talk to your exotic hardware, when ssh is gone and you're running for the ultimate login...
I've got an old IBM thinkpad 340, with only 4 MB RAM, and I thought to use it as a serial terminal, boot from floppy on a ramdisk and forget everything else.
There are other minicom-ready floppy distros but I can't find one that fits in 4 MB RAM so I made my own. This is my little linux toy!
Floppy raw image:  ==> pitux-0.3.3.img <==
    md5: c05b7657c7dfe7a70997fd2de880f1b4 pitux-0.3.3.img
    sha1: 99deea4b38f618109d8994f5057da5720adb26e9 pitux-0.3.3.img
CD-ROM iso image:  ==> pitux-0.3.2.iso <==
    md5: 81098e2934e173b260d40da7fe12f11f pitux-0.3.2.iso
    sha1: 9efe8ca5602526ac21e82f26ccbfc589b6a58ca7 pitux-0.3.2.iso

Floppy creation, Linux:
insert a blank floppy in your PC, data on floppy will be lost!
cd /tmp
md5sum pitux-X.Y.Z.img
dd if=pitux-X.Y.Z.img of=/dev/fd0
(newer systems might use sudo dd if=pitux-X.Y.Z.img of=/dev/sdb Use fdisk to be sure)
when the prompt is back (hopefully without errors) put the floppy in the machine you would like to use and boot from floppy.
to test it with qemu:
qemu -fda pitux-X.Y.Z.img -boot a
qemu -cdrom pitux-X.Y.Z.iso -boot d
Persistent configuration:
a shiny new feature of my toy now let you drop into the floppy root three minirc.* files, during the boot sequence if they are found there they are used to overwrite the same files on the ramdisk so you can have you own minicom configuration. If the script does not find the second of them you are guided through an interactive configuration of the minicom instance on the 1st tty.
The files must have these names:
minirc.dfl: default config file [ttyS0,56700,8n1]
minirc.tty1: config file for the respawned minicom on tty1 [ttyS0,38400,8n1], good for a default login over serial line on a standard x86 linux machine
minirc.tty2: use it as you like just call minicom as:

minicom -c on tty2
You'll find ready to use samples in /floppy/examples.
So you can mount the floppy (or loopmount the image) under any linux, write your minirc.* files with these names or you can configure minicom as you need from within PiTuX and then save your modified files with this command "persist"... oh ALT+F2 gives you a shell :-):
~ # persist
minirc.dfl saved on floppy
minirc.tty1 saved on floppy
minirc.tyy2 saved on floppy
sync floppy... ok
~ # _
The files are copied back on the floppy saved for the next reboot.
Bootable CD-ROM, Linux:
Here is a very small iso image that use isolinux:
it still works with just 4 MB RAM, but given it's on a really readonly media you can't save any configuration.
So once you're dropped into minicom configure it at your needs, save as default and restart minicom, your config will stay until reboot.
Also here ALT+F2 gives you a simple shell from where you can start another minicom with other settings:

minicom -c on tty2

No comments:

Post a Comment