The default editor for crontab is vi. To use another editor simply do the following from a bash shell (Default shell accounts are bash).

In this case we are setting pico as the editor.

export VISUAL='pico -w'
crontab -e

This example script dumps a screenshot of a URL to a specified file.

#!/bin/sh

Xvfb :1 -screen 0 1024x768x24 &
DISPLAY=:1 mozilla -width 1024 -height 768 http://www.kattare.com/ &
sleep 5
DISPLAY=:1 import -window root captured.png
killall mozilla
killall Xvfb

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They're created when a process on a NFS client has an executable file open and that file gets unlinked. (deleted) In other words, don't delete files that processes are currently using.

This tends to happen with log files, where you want to pare down the log file but don't want to restart the server process creating the logs. In this case what you can do instead is use:

cat /dev/null > logfile

Where logfile is the name of the log you want to pare down.