How do I enable / disable two-up printing?

Two-up printing is where 2 pages are printed on one side of a paper by shrinking them, putting them side-by-side on a landscape format paper.

This is the usual default for printing text files. To disable this, you'll need to convert it to Postscript, as Postscript files are printed without reformatting:

      textps file.txt | lpr -Pprintername 

If you have a Postscript file, you can reformat them into a 2-up format (or even 4-up format if your eyesight can stand the strain) by filtering them through the psnup tool:

     psnup -2 file.ps | lpr -Pprintername    psnup -4 file.ps | lpr -Pprintername 

You can combine the above two solutions to print text in a 4-up format:

  textps file.txt | psnup -4 file.ps | lpr -Pprintername 

For Windows users, some printer drivers will allow you to set 1-up, 2-up, 4-up and booklet format.