It's my first time for running Android SDK on 64-bit Linux (Ubuntu Precise). The Android SDK does not work out of the box for x64 environment. ADB fails to run due to the missing libraries. Emulator also fails and so on.
Here is my note on fixing issues. Hope it might help someone who come after this.
The good old handy shortcut Ctrl+Alt+Backspace for restarting X Window has been disabled since Ubuntu 9.04 Jaunty Jackalope (reference). The reason is preventing Windows users from accidentally reboot his/her desktop. Sound reasonable for me.
By the way, sometimes X Window fails to load and you need something to fix it quickly. After little investigation, I found a new key-combo for restarting X in recent Ubuntu releases: