When running IDLE from the terminal on Ubuntu, I get the following error:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/home/serwy/python/cpython/Lib/tkinter/__init__.py", line 1442, in __call__
    return self.func(*args)
  File "./idlelib/GrepDialog.py", line 70, in default_command
    self.grep_it(prog, path)
  File "./idlelib/GrepDialog.py", line 90, in grep_it
    block = f.readlines(100000)
  File "/home/serwy/python/cpython/Lib/codecs.py", line 300, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe4 in position 120: invalid continuation byte

The reason why IDLE closes suddenly on Windows is described in issue13582.