For question 2, you can only use the override command when copying (and modifying) a device from the instance’s profile(s) into its own config. Once it has been copied into its own config you cannot use override again and must use set to modify it.
It was a question about the capacity of “config /run/lxd_config/9p”. I have confirmed again that it is separate from the problem that does not work. I’m Sorry.
Thank you. i solved below command
.# lxc config device set lbg root size=40GB