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<TITLE>The Linux keyboard and console HOWTO: Scrolling</TITLE>
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console!scrolling
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-->
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scrolling, console
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There are two ways to get a screen to scroll.
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The first, called `hard scrolling', is to leave the text in
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video memory as it is, but change the viewing origin. This is
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very fast.
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The second, called `soft scrolling', involves moving all screen text
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up or down. This is much slower.
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The kernel console driver will write text starting at the top of
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the video memory, continuing to the bottom, then copy the bottom
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part to the top again, and continue, all the time using hard scrolling
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to show the right part on the screen.
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You can scroll back until the top op the video memory by using
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Shift-PageUp (the grey PageUp) and scroll down again using
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Shift-PageDown (the grey PageDown), assuming a default keymap.
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The amount of scrollback is thus limited to the amount of video memory
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you happen to have and you cannot increase this amount.
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If you need more scrollback, use some program that
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buffers the text, like less or screen - by using
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a buffer on disk you can go back to what you did last week.
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(One can set the amount of scrollback for xterm by
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adding a line like XTerm*saveLines: 2500 in .Xresources.)
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Upon changing virtual consoles, the screen content of the old VT
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is copied to kernel memory, and the screen content of the new VT
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is copied from kernel memory to video memory. Only the visible screen
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is copied, not all of video memory, so switching consoles means
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losing the scrollback information.
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Sometimes, hard scrolling is undesirable, for example when the hardware
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does not have the possibility to change viewing origin. The first
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example was a Braille machine that would render the top of video
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memory in Braille. There is a kernel boot-time option no-scroll
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to tell the console driver not to use hard scrolling.
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See bootparam(7).
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