Ubuntu18.04 need long time to startup in root account.

[lisiur]

I build a empty project on Ubuntu18.04 and startup app using cmd ./target/release/app, and all is just fine.
But when I exec sudo su , and then exec ./target/release/app again it takes a long time to startup(about 10s).

My tests:

OS	user	cmd	result
Ubuntu18.04	normal	./target/release/app	fine
Ubuntu18.04	normal	sudo ./target/release/app	fine
Ubuntu18.04	root	./target/release/app	stuck
Ubuntu18.04	root	sudo ./target/release/app	fine

I also tested on Ubuntu20.04 and all is fine.