Re: [ptxdist] Backspace not working in terminal (using ssh)

[Michael Olbrich <m.olbrich@pengutronix.de>]

On Thu, Mar 21, 2019 at 03:24:48PM +0000, Ian Abbott wrote:
> On 21/03/2019 13:33, Michael Olbrich wrote:
> > On Thu, Mar 21, 2019 at 12:46:40PM +0000, Ian Abbott wrote:
> > > On 20/03/2019 15:41, Michael Olbrich wrote:
> > > > On Wed, Mar 20, 2019 at 12:41:47PM +0000, Ian Abbott wrote:
> > > > > On 20/03/2019 09:15, Dold, Wolfram wrote:
> > > > > > On Tue, 2019-03-19 at 17:42 +0000, Ian Abbott wrote:
> > > > > > > On 19/03/2019 12:33, Dold, Wolfram wrote:
> > > > > > > > Hi Ian,
> > > > > > > > On Tue, 2019-03-19 at 12:06 +0000, Ian Abbott wrote:
> > > > > > > > > On 19/03/2019 09:17, Dold, Wolfram wrote:
> > > > > > > > > > Hi there,
> > > > > > > > > > when we connect via ssh to our embedded device, the backspace key does not work.
> > > > > > > > > > During the analysis we found out that the passage
> > > > > > > > > > 
> > > > > > > > > > # This fixes the backspace when telnetting in.
> > > > > > > > > > if [ "$TERM" != "linux" ]; then
> > > > > > > > > >              stty erase ^H
> > > > > > > > > > fi
> > > > > > > > > > 
> > > > > > > > > > from the file '/etc/profile' contained in ptxdist.
> > > > > > > > > > 
> > > > > > > > > > Now I want to ask, how best to fix this behavior?
> > > > > > > > > > Can the passage simply be omitted? (At least the comment lets me assume that, because there 'telnet' is
> > > > > > > > > > mentioned
> > > > > > > > > > and
> > > > > > > > > > that is no longer necessarily state of the art).
> > > > > > > > > > Or does omitting it lead to other unwanted side effects?
> > > > > > > > > > 
> > > > > > > > > > Any help would be appreciated.
> > > [snip because it's getting a bit long]
> > > 
> > > > > I've no idea why that bit of the /etc/profile file is there, but I guess it
> > > > > must have suited one of the PTXdist developers at the time.  A "git blame"
> > > > > only revealed that the whole file was added in 2006, so I don't know how
> > > > > relevant that part of it is today.
> > > > 
> > > > This code was moved around some more. It was actually introduced in the
> > > > initial import from CVS in 2003 :-). Telnet works just fine without this,
> > > > so I guess this is no longer needed.
> > > 
> > > Perhaps it was there for the Windows Telnet client which seems to send ASCII
> > > BS when the "Backspace" key is pressed and ASCII DEL when the (less
> > > conveniently placed) "Delete" key is pressed.  This mimics the codes sent by
> > > the VT-102 "Backspace" and "Delete" keys which were both conveniently
> > > placed.
> > > 
> > > The Windows telnet client has a -t option to set the terminal type to one of
> > > "vt100", "vt52", "ansi", or "vtnt", but it doesn't pass the selected
> > > terminal type to the server, and this doesn't seem to have any effect on the
> > > codes sent by the "Backspace" and "Delete" keys.  The TERM environment
> > > variable ends up getting set to "vt102" by default on my PTXdist systems if
> > > a terminal type hasn't been passed through by the Telnet client.  I don't
> > > know if that is configurable.
> > > 
> > > The Windows Telnet client isn't installed by default, but can still be
> > > installed as a "Windows Feature".  I guess most people who used it would
> > > have switched to something like PuTTY by now.
> > 
> > I'm pretty sure it was a Linux issue. I remember having problems like this
> > a long time ago.
> > 
> > > > I'll be happy to apply a patch that removes this.
> > > 
> > > I'm worried that doing so might annoy some people who expect the existing
> > > behavior.
> > 
> > I'd rather fix a real problem. If it causes issues, then we'll try to find
> > a solution.
> 
> Changing it would probably annoy gtkterm users, and annoy minicom users less
> so.  For both of those, the Backspace key sends BS by default. There is an
> option to change it to DEL in minicom, but no such option in gtkterm (or if
> it exists, it is well hidden!).  (Personally, I prefer minimalist, dumb
> serial terminal emulators such as picocom, nanocom, and microcom which just
> run inside a local terminal session.)

Ok, I did some testing and now I'm rather confused. I tested minicom,
microcom and gtkterm on the serial port and putty (on Linux) via serial
port and telnet and a normal telnet.

In all cases backspace and delete work as expected with 'stty erase ^H' and
'stty erase ^?'.

Am I missing something here or is something magically doing the right thing
in the background?

Michael

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