emacs: how to delete a block of region

Mark (Ctrl+Space) the beginning of first line and move cursor to the the last line, and move it to the right n chars. Then do “Alt+x kill-rectangle” (Ctrl+x r k). This command can be used to delete any rectangular block of text, not just at the beginning of lines.

From: http://xahlee.org/emacs/emacs.html

Linux:commands: how to kill jobs in background

If you have jobs running in background, you could kill them by the easier way than finding their PID and kill them. Just use the command jobs to find which job is running in background, and then pick up the job you want to kill, use kill %1 (here 1 is the job number)