To add the current line number of point to the mode line, enable Line Number mode with the command M-x line-number-mode. The line number appears before the buffer percentage pos, with the letter `L' to indicate what it is. See section Minor Modes, for more information about minor modes and about how to use this command.
If the buffer is very large (larger than the value of
line-number-display-limit), then the line number doesn't appear.
Emacs doesn't compute the line number when the buffer is large, because
that would be too slow. If you have narrowed the buffer
(see section Narrowing), the displayed line number is relative to the
accessible portion of the buffer.
Emacs can optionally display the time and system load in all mode lines. To enable this feature, type M-x display-time. The information added to the mode line usually appears after the buffer name, before the mode names and their parentheses. It looks like this:
hh:mmpm l.ll
Here hh and mm are the hour and minute, followed always by `am' or `pm'. l.ll is the average number of running processes in the whole system recently. (Some fields may be missing if your operating system cannot support them.)
The word `Mail' appears after the load level if there is mail for you that you have not read yet.