couldn't set tty to ppp discipline invalid argument

Symptom: the following messages appear before connection is established:

 

Serial connection established.
Couldn't set tty to PPP discipline: Invalid argument
Hangup (SIGHUP)

Diagnosis: pppd has failed to change the pty over to runit in PPP mode. This may be because you have no ppp_asyncmodule built for your kernel. Most kernels are built with thisalready, but if you have customised your kernel you may not have builtit.

Solution: rebuild your kernel with CONFIG_PPP_ASYNC set. Whileyou are at it, you should set CONFIG_PPP as well, and both should beset to "m" so that they are built as modules. We've found they don'twork compiled statically.

重新配置内核（Device Drivers->Network device support->PPP support），把ppp相关的都选上