why not linux auto start

>I suddernly find that linux should start only be nios2-terminal. Why?

>It is a big problem if it is to be a product.

Linux does boot automatically

>1. power on

>2. nothing happens about linux

What do you mean by that?

>3. start nios2-terminal

>4. linux coming.....

If you mean you get no console, that's correct. because you probably only use the nios2-terminal through jtag-uart as a console. If you have a UART in your design you could use that one as a console port by adding console=ttyS0 to the kernel parameters (during kernel config). Then you can use for example minicom (linux) or hyperterminal (windows) to connect to the board through your serial port. Advantage of this setup is that you have your JTAG free to use for SignalTap or other debugging options.

>why? how to let linux auto start up itself?

It does, you just don't see it.

I hope this is an answer to your question...

EDIT:

I saw you added the ehternet soft-powerup comments. This is probably because the ethernet for some reason is not enabled untill you use it (dhcpcd) when you uncomment the dhcpcd line in your rc the ethernet will be enabled at boot time.