Re: Ubuntu stty

[Bob Proulx]

Tom Lake wrote:
> I have an ASR-33 Teletype on ttyS0 which can only output uppercase
> characters that I'm trying to use as a serial console.

I like it.

> My getty specifies -U to allow for uppercase terminals.
> ...
> As you can see, iuclc is clearly in effect but
> the conversion from uppercase to lowercase isn't being done.
> No commands work, and I had to create a user with an uppercase-only
> password just to be able to log in at all.

I can recreate your problem on my Debian Linux 2.6.26 kernel.  The
'olcuc' has effect but 'iuclc' doesn't seem to function at all.  I may
be missing something but at this point I agree with you that this is a
bug and one that I would not have expected to see in such an old
interface.  I guess no one uses uppercase only terminals anymore. :@)

> Shouldn't stty have converted the uppercase input to lowercase?

The 'stty' command sets tty driver controls.  It isn't the actual code
that does any of these conversions.  The driver in the kernel is
responsible for that behavior.  The 'stty' command is simply one
interface to change or display those settings.  To me the problem
appears to be in the Linux kernel.

> If I set iuclc on tty0 (the normal console) it works as expected and
> I can turn on Caps Lock and still execute commands and cp tty0 test
> does put lowercase characters in test regardless of the state of Caps
> Lock.

The Linux console uses a different driver from the serial terminal
which uses a different driver from the pseudo-tty driver used for
terminals on the graphical display.  It is certainly possible for them
to suffer from different bugs and differing behavior.

> Is this a bug in stty?

I don't think the bug is in stty.  It would only be setting ioctl
values and displaying those values.  The kernel driver would be
responsible for all of the work.  The kernel is what is actually
reading and writing characters.  Plus the behavior is working for
ptys.  At first glance in my mind everything is pointing to a problem
in the Linux tty serial driver.  I think you need to report the
problem against the Linux kernel.  That can be a harsh place for
people to start.  Since you are using Ubuntu I recommend that you
report the problem against the Ubuntu linux-image-2.6-686 package and
get some help working through the problem from the distro package
team.  This is interesting to me so if you would be so kind please let
me know how you report it so that I can track it and perhaps help in
the testing.

> If so, I'd like to get a fix so I can use my terminals in a local
> antique computer museum.

I think that is a pretty cool idea.  I hope you can do this.

Bob