Unblock bash after Ctrl-S

S is so near to A, and we all use Ctrl-A all the time. So, it is easy to hit Ctrl-S by error, and that will make bash freeze.

What Ctrl-S does is to pause flow-control (XOFF), that means that the terminal will accept inputs but will not show the output of anything.

To restart flow-control, simply give Ctrl-Q (XON) and you will see all your inputs compare on the screen.

Reference: http://en.wikipedia.org/wiki/Software_flow_control