console & tty differ

在本机上，用户可以使用alt-f1~fn切换控制台，看起来感觉存在多个屏幕，这种虚拟控制台对应tty1~n

但实际上机器只有一个屏幕，也就是我们看到的这个屏幕，对应console。

可以理解为console指向激活的那个tty（详细来说不是，tty0才是激活的那个tty，准确地说是激活的那个tty才将输出显示到 console）

历史上，console指主机本身的屏幕键盘，而tty指用电缆链接的其它位置的控制台（仅包含屏幕和键盘）

------------------
problem:
VDSL login:
VDSL login: root
login[250]: root login on 'console'
-sh: can't access tty; job control turned off

from busybox source code doc:

Job control will be turned off since your shell can not obtain a controlling terminal. This typically happens when you run your shell on /dev/console. The kernel will not provide a controlling terminal on the /dev/console device. Your should run your shell on a normal tty such as tty1 or ttyS0 and everything will work perfectly. If you REALLY want your shell to run on /dev/console, then you can hack your kernel (if you are into that sortof thing) by changing drivers/char/tty_io.c to change the lines where it sets "noctty = 1;" to instead set it to "0". I recommend you instead run your shell on a real console...

fix:
change file
old:
::respawn:/sbin/getty -L console 115200 vt100
new:
::respawn:/sbin/getty -L ttyS0 115200 vt100

log:
VDSL login: root
login[250]: root login on 'ttyS0'
#