Why is my terminal freezing up?

Did you press Ctrl+S by any chance? It's the terminal pause key that stops all output until you press Ctrl-Q to resume.

A good general way to diagnose mysterious hangs:

1. open a(nother) terminal, and use ps axo pid,wchan:32,cmd to find the other process id
2. note the wchan column, which should tell you whether it's stuck in the kernel
3. run sudo strace -p PID inserting the pid of that process; paste that into a bug report or question

If there's anything aside from just a dash in the wchan column, then the process is in the kernel doing something. Some typical values:

• futex_wait_queue_me - waiting on a futex for another thread in the same process
• poll_schedule_timeout - waiting for network or interprocess communication, or just sleeping for a while
• pipe_wait - reading/writing a pipe

There are thousands of possibilities so I can't list them all. See What is the "Waiting Channel" of a process? for more.