I run debian jessie 8.0, when I turn on the pc my booting prompt become dark for a moment and then all the characters become bold. Is it normal? How can I change the appearence of booting prompt?
I ran across this issue recently installing a new server that wanted me to log in to a tiny microprint login prompt. This was my (Debian-specific) fix.
You can set your console font like so:
$ sudo dpkg-reconfigure console-setup
First, select encoding. You almost certainly want UTF-8.
Then, pick character set. You probably want the default. If in doubt, and you use English or a similarly-written language, you probably want Latin1/Latin5.
Now, choose your console font. The fonts "Fixed", "Terminus", "Terminus Bold", and "VGA" seem to have the best selection in terms of font sizes available, especially "Terminus/Terminus Bold". (I found Terminus Bold to be the easiest on the eyes; your mileage may vary.)
Lastly, choose your font size. A little explanation is in order... 8x14 and 8x16 are on the small end of what you can get, and 14x28 and 16x32 are on the large end. If your console text was initially tiny (like mine was) and you want something larger, you probably want 14x28 or 16x32.
Alas, to make the changes permanent, we will need to create a startup script. Enter this command:
$ sudo nano /etc/init.d/setupcon-initial
Give the file exactly these contents:
To save and exit, press control-x, then y, then enter.
Then issue these commands to make the new script executable, and to register it to run by default:
$ sudo chmod 755 /etc/init.d/setupcon-initial $ sudo update-rc.d setupcon-initial defaults
You can safely ignore any warning about missing tags and overrides; the script will work fine without them.
The next time you reboot, your console login prompts should show in your preferred console font and size. (I tested this in Debian 9/Stretch before posting it because my Debian 8/Jessie server does not have an attached monitor. Principle should be the same either way.)
Usually the effect you mention is due to the kernel changing the video mode during booting. At the same time, it may load a new font to compensate (or to exploit increased resolution).
Here are a few articles discussing this: