linum-mode
linum-mode is an interactive autoloaded compiled Lisp function in `linum.el
'.
(linum-mode &optional ARG)
Toggle display of line numbers in the left margin (Linum mode).
With a prefix argument ARG, enable Linum mode if ARG is positive,
and disable it otherwise. If called from Lisp, enable the mode
if ARG is omitted or nil.
Linum mode is a buffer-local minor mode.