[gentoo-amd64] Terminal control codes

[gentoo-amd64] Terminal control codes

[Peter Humphrey]

Thanks to all who helped me with my SATA and mdraid problem - I'll answer
when I've finished rebuilding the system and can reply more comfortably and
comprehensively.

Meanwhile I've another two small problems - how to control the virtual
terminal; its scrollback buffer and setterm codes (I'm not talking about X
here). Somewhere in the documents I read that the size of the scrollback
buffer can be declared in a kernel command, something like
"fbcon=scrollback:1024k. When I do that though, the kernel boots ok but
scrollback is disabled.

Secondly, another FAQ says to send setterm codes to /dev/vc/X, but since (I
assume) the rise of udev those devices don't exist any more.

Does anyone here know how to play these small tricks?

--
Rgds
Peter.


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[gentoo-amd64] Re: Terminal control codes

[Duncan]

"Peter Humphrey" <prh@gotadsl.co.uk> posted
20070102170933.15EE52B6F39@smtp.nildram.co.uk, excerpted below, on  Tue,
02 Jan 2007 17:09:28 +0000:

> Somewhere in the documents I read that the size of the scrollback
> buffer can be declared in a kernel command, something like
> "fbcon=scrollback:1024k. When I do that though, the kernel boots ok but
> scrollback is disabled.

Naturally, something like fbcon would require a framebuffer console, a
kernel (pre-compile) config option.  For VGACON...

You may be looking for the video= parameters, in particular
video=scrollback.  See section 5.2 of the bootprompt HOWTO, here:
http://tldp.org/HOWTO/text/BootPrompt-HOWTO.

However, IIRC the kernel folks dramatically increased the default
recently, and with kernel 2.6.19 at least (I think it was before that but
can't remember when), I've been able to eliminate that parameter from my
grub.conf entirely, and had to go look it up.  I can now scrollback the
/entire/ boot sequence, from the login prompt, all the way back thru where
init and the Gentoo initscripts take over, back thru the many pages of
kernel init itself, and even before that, where grub prints its last
output as it loads the kernel before switching to it.  I'd never seen
those lines before, as they are normally scrolled off the top of the
screen by the first kernel messages before the monitor even resets from
the grub menu graphic mode!

There are a couple caveats, however.  First, switching between VCs loses
the scrollback context, so all you have is what's actually on the screen. 
Second and this is what was actually preventing me scrolling back further
for awhile, if you reset the console font (Gentoo's consolefont service),
it resets the scroll buffer.  Since the consolefont service starts
relatively late in the process, using it means you lose most of the
boot-time scrollback, altho you can still get most of the info from syslog
and/or dmesg -- but not that last bit of grub output! =8^(

In addition to setting vga=0x0133 for a normal 132x44 character console
(720x400 px), I /had/ been setting the consolefont to gr737c-8x6, giving me
an even higher resolution while still very readable, but I've disabled
that now, sticking with 132x44, so I can scrollback the entire boot when
necessary. 132x44 is good enough for the CLI VC.  If I need more than
that, I'll start KDE and use konsole.  There may be a way to compile that
font into the kernel and use it by default, but I'm not advanced enough to
know how to do it, so...

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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Re: [gentoo-amd64] Re: Terminal control codes

[Peter Humphrey]

On Wednesday 03 January 2007 04:06, Duncan wrote:

> You may be looking for the video= parameters, in particular
> video=scrollback.  See section 5.2 of the bootprompt HOWTO, here:
> http://tldp.org/HOWTO/text/BootPrompt-HOWTO.

Ah. Thanks for the pointer.

> Second and this is what was actually preventing me scrolling back further
> for awhile, if you reset the console font (Gentoo's consolefont service),
> it resets the scroll buffer.  Since the consolefont service starts
> relatively late in the process, using it means you lose most of the
> boot-time scrollback, altho you can still get most of the info from
> syslog and/or dmesg -- but not that last bit of grub output! =8^(

I was using locales to give me ISO-8859-1 and -15 character sets, but glibc 
is buggy in this area and I've had to keep recreating the locales with 
localedef. Now it occurs to me to use UTF-8, so I shouldn't need the 8859 
codes. Thus it becomes feasible to try removing the console-font service - 
thanks again.

> In addition to setting vga=0x0133 for a normal 132x44 character console
> (720x400 px), I /had/ been setting the consolefont to gr737c-8x6, giving
> me an even higher resolution while still very readable, but I've disabled
> that now, sticking with 132x44, so I can scrollback the entire boot when
> necessary.

I use vga=0x31A on this 19", 1600x1200 flat panel. If I run nvidia-drivers 
this gives me a screen of 160x 64, or if I use the nv kernel module I get 
200x75. I find both of those legible, though the latter is getting a bit 
small - and of course all that screen redrawing takes time in a long 
emerge.

-- 
Rgds
Peter
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Re: [gentoo-amd64] Terminal control codes

[Peter Humphrey]

On Tuesday 02 January 2007 17:09, I wrote:

> Secondly, another FAQ says to send setterm codes to /dev/vc/X, but since
> (I assume) the rise of udev those devices don't exist any more.

Can anyone help me here? I need to know where to send "setterm -blank 0" to 
prevent screen blanking on vc1-6 and 12. Or have I to find the blanking 
code in the source (which source?) and switch it off there? Maybe there's 
an option to a configure script somewhere.

-- 
Rgds
Peter
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Re: [gentoo-amd64] Terminal control codes

[Paul de Vrieze]

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On Sunday 14 January 2007 18:36, Peter Humphrey wrote:
> On Tuesday 02 January 2007 17:09, I wrote:
> > Secondly, another FAQ says to send setterm codes to /dev/vc/X, but since
> > (I assume) the rise of udev those devices don't exist any more.
>
> Can anyone help me here? I need to know where to send "setterm -blank 0" to
> prevent screen blanking on vc1-6 and 12. Or have I to find the blanking
> code in the source (which source?) and switch it off there? Maybe there's
> an option to a configure script somewhere.

Try /dev/vcs{1..12} or /dev/tty{1..12}

Paul

-- 
Paul de Vrieze
Gentoo Developer
Mail: pauldv@gentoo.org
Homepage: http://www.devrieze.net

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Re: [gentoo-amd64] Terminal control codes

[Peter Humphrey]

On Monday 29 Jan 2007, Paul de Vrieze wrote:
> On Sunday 14 January 2007 18:36, Peter Humphrey wrote:
> > On Tuesday 02 January 2007 17:09, I wrote:
> > > Secondly, another FAQ says to send setterm codes to /dev/vc/X, but
> > > since (I assume) the rise of udev those devices don't exist any more.
> >
> > Can anyone help me here? I need to know where to send "setterm -blank
> > 0" to prevent screen blanking on vc1-6 and 12. Or have I to find the
> > blanking code in the source (which source?) and switch it off there?
> > Maybe there's an option to a configure script somewhere.
>
> Try /dev/vcs{1..12} or /dev/tty{1..12}

Nice idea, but no joy. From a little code skimming I've done it seems 
that /dev/vcsN is the text content of the console, while /dev/vcsaN is 
its "text/attributes", whatever that means. I assume that /dev/ttyN is just 
the device to which a program sends things for display.

It looks as though a new format of codes is needed to switch blanking off: 
perhaps an escape string? That's a straw I'm clutching at, notice ;-)

-- 
Rgds
Peter
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