Quieter Boot
One of my PCs has a rather unique boot sequence:
Syslinux, from an SD card and configured to chain load the next stage.
A pre-boot environment, FreeDOS, from the SD card. The pre-boot environment does the following:
- Check if a USB stick is inserted. If there is one inserted, then continue to the next stage in the boot sequence. Otherwise...
- Display a message asking the user to insert the USB stick.
- Wait 20 seconds for the USB stick to be inserted.
- If the USB stick is inserted within those 20 seconds, then continue to the next stage in the boot sequence, but pass a flag indicating to boot into a maintenance mode. Otherwise...
- Go to a DOS prompt.
FreeDOS makes a great pre-boot environment - it's super fast to boot, very small and you don't have to faff about producing custom initrds. I used Bret Johnson's USBDOS drivers to do the USB stick detection.
kexec-loader, from the SD card (via Linld) and configured to boot the next stage from the USB stick. I used kexec-loader here because it contains USB 2.0 drivers, so loading the next stage is much faster than using the BIOS's legacy emulation mode.
The fantastic Tiny Core Linux, from the USB stick, booting into X with some custom extensions.
Now, this all works well but I wanted to reduce the copious level of noise (messages) displayed while booting to a minimum.
Syslinux
Syslinux itself makes some noise. I had to patch it to make it quiet. You can see the patch is mostly about supressing puts and printf. You can also see that the copyright notice is still displayed.
I also added some new control codes to Syslinux display files:
STX (\002): Home the cursor without clearing the screen. I found this useful if I displayed a message in the centre of the screen. Any text that was displayed afterwards was less likely to cause the screen to scroll.
SOH (\001): Hide the cursor. Useful for a completely black screen.
ETX (\003): Change palette register 1 (normally blue) to bright white, using INT 10H 1000H.
In the end I used just ETX in my Syslinux display file.
FreeDOS
Confession: I didn't bother supressing messages in FreeDOS. Therefore, the FreeDOS copyright notice was displayed momentarily until the next stage. If you want to remove this notice, you'll have to patch FreeDOS and recompile from source.
I did use nansi.sys to display a greeting message in blue before starting kexec-loader with Linld:
echo ESC[34mWelcome!ESC[0m
linld image=vmlinux initrd=initrd.img ...
(Note: you'll need to get the literal ESC character into your bat file, e.g. using ^V in Vim and then pressing the Escape key).
Of course, since we used ETX in the Syslinux display file, this message was actually shown in bright white.
kexec-loader
To hide all further messages until X starts, I passed the following kernel parameters to kexec-loader using Linld:
quiet
console=tty2
vt.default_blu=0,0,0,0,255,0,0,0,0,0,0,0,0,0,0,0
vt.default_grn=0,0,0,0,255,0,0,0,0,0,0,0,0,0,0,0
vt.default_red=0,0,0,0,255,0,0,0,0,0,0,0,0,0,0,0
quiet hides most kernel log messages, but unfortunately not all of them - as the description of this parameter says:
quiet [KNL] Disable most log messages
console=tty2 makes all kexec-loader's kernel messages go to tty2 - i.e. they are hidden because tty1 is shown by default.
The vt.default_* parameters change the Linux kernel's console palette. As you can see, I set every colour in the palette to black, except palette colour 4. This hid all messages except for those displayed using palette number 4.
The Linux kernel's console palette is in a different order to INT 10H's:
unsigned char color_table[] = { 0, 4, 2, 6, 1, 5, 3, 7,
8,12,10,14, 9,13,11,15 };
Palette colour 4 here corresponds to INT 10H's palette register 1 (i.e. normally blue). So the effect of this is to hide everything except the Welcome! message we displayed in the FreeDOS pre-boot environment.
Tiny Core Linux
To keep Tiny Core Linux quiet, I got kexec-loader to boot it with these parameters:
quiet
vt.default_blu=0,0,0,0,255,0,0,0,0,0,0,0,0,0,0,0
vt.default_grn=0,0,0,0,255,0,0,0,0,0,0,0,0,0,0,0
vt.default_red=0,0,0,0,255,0,0,0,0,0,0,0,0,0,0,0
I repeated vt.default_* because otherwise the Linux kernel resets the palette to the default colours.
I didn't boot with console=tty2 because I wanted the flexibility to display messages later in the boot process.
Summary
My goal was to reduce the amount of noise during boot for a PC booting from Syslinux into FreeDOS then (via Linld) from kexec-loader into Tiny Core Linux.
- I patched Syslinux to remove all messages apart from the copyright one.
- I patched Syslinux with an extra display file control code to turn the blue palette register into bright white.
- I displayed a welcome message in FreeDOS using this colour.
- I started kexec-loader with options to turn all except this colour into black.
- I did the same when starting Tiny Core Linux.
The effect of this is that the following are shown before kexec-loader starts:
- The BIOS blurb.
- The Syslinux copyright message.
- The FreeDOS copyright message.
- The welcome message.
After kexec-loader starts, and until X comes up, only the welcome message is displayed.
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