Plz tell me command using which i can increase the size of my scrollback buffer in red hat linux..
thankz in advance wth regards.

If you're using an xterm-based (gui) application, then it probably depends on the settings of that program. I use konsole, for example, and it has a setting for how much history you want.

In a pure cli terminal I believe it depends on the buffer that's been hard-coded into the kernel video driver you're using, probably vesa. The only way to change that is to recompile your kernel.

There is however a program called screen which provides multiple virtual terminals in cli mode, and I'm pretty sure you can adjust the scrollback buffer there, just like you can with gui consoles.

thanks a super ton for a quick response,
i mean while using command in virtual console,we can see the history of command we used using page-up,down keys
is there any setting to limit those list,like i can only see the last used 10 or 20command not more than that?

Ah, so you mean the command history, and not the scrollback. In the future, if you aren't sure about the terminology, you should take more care to make it clear what you are referring to.

In bash, the command history size is controlled by the environmental variables HISTSIZE and HISTFILESIZE. Other shells probably have similar settings.

There are other useful settings as well, such as HISTCONTROL, where you can set options such as ignoring duplicate entries. The man page for bash will tell you more about them.

BTW, <20 commands is incredibly small. My bash man page says the default is 500 lines. Strange.

Assuming that you're using BASH, this will give you some information about bash history variables.