redirect standard error

Ok, this may be really easy, but please help:

If you have a program that has run amuk and it is continuously spitting
out errors to the terminal, how do you redirect standard error to
something other than the terminal --without-- restarting the program
like : prog 2> /dev/null ?

I just want to get rid of the output so I can use the terminal, or just
redirect the error into a file, but I need to do it without restarting
the program.

Thanks

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