Increasing scroll back length of xterm

Solution 1:

In the manual of xterm, you can find the description of the relevant option:

-sl number
This option specifies the number of lines  to  save  that  have
been scrolled  off the top of the screen.  This corresponds to the
saveLines resource.  The default is “64”.

So you can call

xterm -sl xxx

or create an alias

xterm='xterm -sl xxx'

or set saveLines in your (or the global) Xresources file.