Difference between revisions of "Scrollback buffer"

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(The Easy Way: does this really work?)
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[[Category:Terminal emulators]]
 
[[Category:Terminal emulators]]
Scrollback is a function that is implemented in a text console to allow the user to go back to view the lines of text which have scrolled off the screen. This is made possible by a buffer created just for this purpose between the video adapter and the display device; the scrollback buffer.  Normally, the key combinations of Shift-PageUp or Shift-PageDown allows the user to scroll up or down a page or two by default.
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[[ja:スクロールバックバッファ]]
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{{Merge|Boot debugging|this article should be expanded to cover general framebuffer console tweaks, or should simply be added to boot debugging for those who need more output}}
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Scrollback allows the user to go back and view text which has scrolled off the screen of a text console. This is made possible by a buffer created between the video adapter and the display device called the scrollback buffer.  By default, the key combinations of Shift+PageUp and Shift+PageDown scroll the buffer up and down.
  
However, what if one wishes to keep track of more than that small amount?  During boot this is particularly necessary, as the text scrolls off by quite a few pages.  To solve this need, the scrollback buffer must be increased.  It is a simple process to do so.
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== Expanding the buffer ==
  
The basic buffer size is 32K, equal to approximately 4 half pages of text.  The easy way to increase this is to use a device called fbcon (the framebuffer console).  To find out about fbcon, this [http://www.mjmwired.net/kernel/Documentation/fb/fbcon.txt link] can give you more information.  Just follow these instructions.
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If scrolling up all the way does not show you enough information, you need to expand your scrollback buffer to hold more output. This is done by tweaking the kernel's framebuffer console (fbcon) with the [[kernel parameter]] {{ic|1=fbcon=scrollback:Nk}} where {{ic|N}} is the desired buffer size is kilobytes. The default size is 32k.
  
== The Easy Way ==
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If this does not work, your framebuffer console may not be properly enabled. Check the [https://www.kernel.org/doc/Documentation/fb/fbcon.txt Framebuffer Console documentation] for other parameters e.g. for changing the framebuffer driver.
Edit the appropriate kernel line as used by your bootloader (e.g. {{ic|/boot/grub/menu.lst}} for [[GRUB]], or {{ic|/boot/syslinux/syslinux.cfg}} for [[syslinux]]). Make the following changes:
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* If {{ic|vga=XXX}} exists, delete it.  
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* Append {{ic|XXXfb}}, replacing XXX with the name of your video driver.
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* Append {{ic|fbcon=scrollback:Nk}}, where N is the amount of scrollback desired.
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Then reboot.
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Latest revision as of 07:00, 12 January 2016

Merge-arrows-2.pngThis article or section is a candidate for merging with Boot debugging.Merge-arrows-2.png

Notes: this article should be expanded to cover general framebuffer console tweaks, or should simply be added to boot debugging for those who need more output (Discuss in Talk:Scrollback buffer#)

Scrollback allows the user to go back and view text which has scrolled off the screen of a text console. This is made possible by a buffer created between the video adapter and the display device called the scrollback buffer. By default, the key combinations of Shift+PageUp and Shift+PageDown scroll the buffer up and down.

Expanding the buffer

If scrolling up all the way does not show you enough information, you need to expand your scrollback buffer to hold more output. This is done by tweaking the kernel's framebuffer console (fbcon) with the kernel parameter fbcon=scrollback:Nk where N is the desired buffer size is kilobytes. The default size is 32k.

If this does not work, your framebuffer console may not be properly enabled. Check the Framebuffer Console documentation for other parameters e.g. for changing the framebuffer driver.