Alt key seems not work in xterm. Alt is important for Emacs.
How to make Alt key work in xterm?
Put this in your ~/.Xresources
file:
XTerm*eightBitInput: false
XTerm*eightBitOutput: true
Remember to make it take effect after you change the ~/.Xresource
without restarting the X server by
xrdb -merge ~/.Xresources