Srollback in Console

Message

paulb787 · Post by **paulb787** » Fri Oct 14, 2011 5:04 am

I just learned that you can scroll back in the console with.shift page up and pg down.
I love it. I can only scroll up a little and was wondering.why? If anybody can help.

Thank u

wswartzendruber · Post by **wswartzendruber** » Fri Oct 14, 2011 5:08 am

So is this Konsole or GNOME Terminal...or a plain old TTY?

Aquous · Post by **Aquous** » Fri Oct 14, 2011 12:29 pm

He's talking about plain old TTY.

The amount you can scroll back by is determined by a certain kernel .config setting, however that has a maximum buffer size of, I believe, 256KiB. Which is about one full screen and a half. I don't know why this limitation exists, only that it's hard-coded into the kernel .config.

Post by **John R. Graham** » Fri Oct 14, 2011 1:59 pm

A screen and a half? Dude, this is a text console. 256KiB is enough for over 100 pages of 80x25 text console.

- John

wswartzendruber · Post by **wswartzendruber** » Fri Oct 14, 2011 2:51 pm

Isn't there a kernel configuration setting called "Backbuffer console in system RAM?" It's under Graphics in the Drivers section.

Post by **Chiitoo** » Fri Oct 14, 2011 2:52 pm

I do believe this might be the setting, quoting make menuconfig? ^^

Code: Select all

  │ CONFIG_VGACON_SOFT_SCROLLBACK_SIZE:                                                                   
  │                                                                                                                   
  │ Enter the amount of System RAM to allocate for the scrollback                                         
  │ buffer.  Each 64KB will give you approximately 16 80x25                                                  
  │ screenfuls of scrollback buffer                                                                        
  │                                                                                                                
  │ Symbol: VGACON_SOFT_SCROLLBACK_SIZE [=64]                         
  │ Type  : integer                                                                    
  │ Range : [1 1024]                                                            
  │ Prompt: Scrollback Buffer Size (in KB)                                                                          
  │   Defined at drivers/video/console/Kconfig:37                                                           
  │   Depends on: HAS_IOMEM [=y] && VT [=y] && VGACON_SOFT_SCROLLBACK [=y]          
  │   Location:                                           
  │     -> Device Drivers                             
  │       -> Graphics support                                       
  │         -> Console display driver support                        
  │           -> VGA text console (VGA_CONSOLE [=y])                        
  │             -> Enable Scrollback Buffer in System RAM (VGACON_SOFT_SCROLLBACK [=y])

Edit:

T'was all messed up oddly enough even though in preview it seemed to be fine.

BitJam · Post by **BitJam** » Fri Oct 14, 2011 6:43 pm

In /usr/src/linux/Documentation/fb/fbcon.txt it says:

Code: Select all

2. fbcon=scrollback:<value>[k]

        The scrollback buffer is memory that is used to preserve display
        contents that has already scrolled past your view.  This is accessed
        by using the Shift-PageUp key combination.  The value 'value' is any
        integer. It defaults to 32KB.  The 'k' suffix is optional, and will
        multiply the 'value' by 1024.

You can adjust the size of the scrollback buffer at boot time.

Aquous · Post by **Aquous** » Fri Oct 14, 2011 6:44 pm

John R. Graham wrote:A screen and a half? Dude, this is a text console. 256KiB is enough for over 100 pages of 80x25 text console.

Your text console may be 80x25, but mine is 1280/8x1024/16=160x64.

Having said that, you are right... I forgot I was using fbcondecor, which apparently matters, because I really do only get a screen and a half with that buffer set to 256KiB.

wrc1944 · Post by **wrc1944** » Fri Oct 14, 2011 6:47 pm

Hmmm.
I've used this kernel setting for years. It helps some in tty, but I've only gotten about 30 pages or so more than the default 5-6 pages, IIRC.
Am I missing something? This limited tty scrollback has been a pet peave of mine for ten years, and I've never figured out how to make it any larger, as 1024 seems to be a hard coded limitation.

Code: Select all

# Console display driver support
#
CONFIG_VGA_CONSOLE=y
CONFIG_VGACON_SOFT_SCROLLBACK=y
CONFIG_VGACON_SOFT_SCROLLBACK_SIZE=1024
CONFIG_DUMMY_CONSOLE=y
CONFIG_FRAMEBUFFER_CONSOLE=y
CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY=y
# CONFIG_FRAMEBUFFER_CONSOLE_ROTATION is not set