[systemd-devel] vt220 default for serial console still relevant?

[Bruce A. Johnson]

Reading this discussion about VT220, I'm wondering why that was the
choice and not VT100 (which was also monochrome). And I'm straining my
memory to recall what it was that we had back then that made the VT100
seem so slick and futuristic.

Bruce A. Johnson | Firmware Engineer
Blue Ridge Networks, Inc.
14120 Parke Long Court Suite 103 | Chantilly, VA 20151
Main: 1.800.722.1168 | Direct: 703-633-7332
http://www.blueridgenetworks.com

On 13/07/2020 17:08, Barry wrote:
>
>
>> On 11 Jul 2020, at 20:31, Daan De Meyer <daan.j.demeyer at gmail.com> wrote:
>>
>> 
>> > TERM=linux means Linux console, but that's just too much, as it not
>> > only implies a multitude of ESC sequences specific to the Linux
>> > console, but also indicates that certain ioctls might work. In our own
>> > code we also bind certain behaviour to TERM=linux, as indicator if we
>> > are on the Linux console.
>> >
>> > I am not aware of any widely-supported TERM value that would be a
>> > reasonable subset of all currently used terminals and does color.
>>
>> I did some more research and it turns out VT220 does support colors.
>> My terminal emulator (Konsole) just doesn't seem to support it. I
>> installed xterm (which explicitly advertises support for VT220 escape
>> codes) and got colored output as expected.  I guess this means it's
>> up to Konsole to support more of VT220 if I want this to work
>> seamlessly (or I switch terminals to xterm).
>>
>
> No vt220 does not support colour. I used to work on one and it is
> monochrome hardware.
> Xterm and konsole support extensions beyond vt220 that add in the
> colour support.
>
> Barry
>
>> Thanks for the extra info and context.
>>
>> Daan
>>
>> On Sat, 11 Jul 2020 at 20:04, Lennart Poettering
>> <lennart at poettering.net <mailto:lennart at poettering.net>> wrote:
>>
>>     On Sa, 11.07.20 17:51, Daan De Meyer (daan.j.demeyer at gmail.com
>>     <mailto:daan.j.demeyer at gmail.com>) wrote:
>>
>>     > Hi,
>>     >
>>     > I was playing around with mkosi's qemu support, more
>>     specifically adding
>>     > the -nographic option to have the virtual machine output in my
>>     terminal
>>     > instead of a separate window. After figuring out that I had to add
>>     > console=ttyS0 to mkosi's kernel command line, I got the output
>>     from the vm
>>     > in my terminal as expected. However, because systemd defaults
>>     to TERM=vt220
>>     > for serial consoles, the output is not colorized. I searched
>>     around a bit
>>     > and found that this is done for compatibility reasons. Will
>>     there ever be a
>>     > point where we can switch the default to something that
>>     supports colors
>>     > (like TERM=linux)?
>>
>>     TERM=linux means Linux console, but that's just too much, as it not
>>     only implies a multitude of ESC sequences specific to the Linux
>>     console, but also indicates that certain ioctls might work. In
>>     our own
>>     code we also bind certain behaviour to TERM=linux, as indicator if we
>>     are on the Linux console.
>>
>>     I am not aware of any widely-supported TERM value that would be a
>>     reasonable subset of all currently used terminals and does color.
>>
>>     > I managed to get around the problem by overriding
>>     serial-getty at ttyS0 and
>>     > setting Environment=TERM=linux explicitly but it's a bit of a
>>     pain and has
>>     > to be added to every rootfs that wants to support colored
>>     output on its
>>     > serial console.
>>
>>     Unfortunately we can't guess the right terminal, we cannot propagate
>>     TERM=xterm or TERM=linux depending if you invoke qemu on an xterm or
>>     from a Linux console, hence the best thing we can do is stick to a
>>     reasonably powerful subset that is likely going to exist everywhere,
>>     and that's vt220 right now, as noone had a better suggestion so
>>     far...
>>
>>     Lennart
>>
>>     --
>>     Lennart Poettering, Berlin
>>
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