From the documentation(http://www.kernel.org/doc/Documentation/devices.txt):

    /dev/tty        Current TTY device
    /dev/console    System console
    /dev/tty0       Current virtual console

In the good old days /dev/console was System Administrator console. And TTYs were users' serial devices attached to a server.
Now /dev/console and /dev/tty0 represent current display and usually are the same. You can override it for example by adding console=ttyS0 to grub.conf. After that your /dev/tty0 is a monitor and /dev/console is /dev/ttyS0.

An exercise to show the difference between /dev/tty and /dev/tty0:

Switch to the 2nd console by pressing Ctrl+Alt+F2. Login as root. Type "sleep 5; echo tty0 > /dev/tty0". Press Enter and switch to the 3rd console by pressing Alt+F3.
Now switch back to the 2nd console by pressing Alt+F2. Type "sleep 5; echo tty > /dev/tty", press Enter and switch to the 3rd console.

You can see that "tty" is the console where process starts, and "tty0" is a always current console.


/dev/tty是当前进程控制的tty设备,而tty0则是当前的控制台。当你在一个终端执行“sleep 5; echo tty0 > /dev/tty0”命令后,切换到其它终端,则tty0会在你切换后的终端显示。而执行“sleep 5; echo tty > /dev/tty”命令后,无论切换到那个终端,tty始终会在输入命令的终端显示。