mac - Trying to grep the output of fs_usage with poor results

I'm trying to figure out what process is periodically and silently erasing the contents of the /etc/hosts file on a Mac. I tried using:

sudo fs_usage | grep hosts

but it only generates a few seconds of output and then returns me to the command prompt, after which trying to restart fs_usage tells me:

ktrace_start: Resource busy

Once that happens, the only way I know how to re-enable fs_usage is to restart the computer, as I can't find either fs_usage or the ktrace process. Piping the output of grep to a text file generated nothing and behaved the same way.

1. Why is grep ceasing all output after a few seconds?


2. How can I make fs_usage available again without restarting?