How to close pppd in init step?
 

No need to dial via pppoe, my pc is connected with router,the router will dial and connect to internet.

journalctl -xb > /tmp/init.tx
cat /tmp/init.txt
AT the end of the file.

Aug 19 09:43:27 hwy pppd[496]: Timeout waiting for PADO packets
Aug 19 09:43:27 hwy pppd[496]: Unable to complete PPPoE Discovery
Aug 19 09:44:32 hwy pppd[496]: Timeout waiting for PADO packets
Aug 19 09:44:32 hwy pppd[496]: Unable to complete PPPoE Discovery
Aug 19 09:45:37 hwy pppd[496]: Timeout waiting for PADO packets
Aug 19 09:45:37 hwy pppd[496]: Unable to complete PPPoE Discovery
Aug 19 09:46:42 hwy pppd[496]: Timeout waiting for PADO packets
Aug 19 09:46:42 hwy pppd[496]: Unable to complete PPPoE Discovery
Aug 19 09:47:47 hwy pppd[496]: Timeout waiting for PADO packets
Aug 19 09:47:47 hwy pppd[496]: Unable to complete PPPoE Discovery
Aug 19 09:48:52 hwy pppd[496]: Timeout waiting for PADO packets
Aug 19 09:48:52 hwy pppd[496]: Unable to complete PPPoE Discovery
Aug 19 09:48:52 hwy pppd[496]: Exit.

How to close pppd in init step?

As you clearly have systemd, you will need to find out the name of the service (it's probably called pppd.service) and disable it with systemctl. You will need to be root to do this. Disabling a service simply takes the link to the service file out of the requirements for the active runlevel targets. Next time you boot, it won't start again.

man systemctl will give you the syntax for the disable command.