Function: line-number-mode

Toggle line number display in the mode line (Line Number mode).
With a prefix argument ARG, enable Line Number mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.

Line numbers do not appear for very large buffers and buffers
with very long lines; see variables `line-number-display-limit'
and `line-number-display-limit-width'.

Variable: line-number-mode

Non-nil if Line-Number mode is enabled.
See the command `line-number-mode' for a description of this minor mode.