Looked wiki, I hope I could restore my op permission after regiteration... if possile

It‘s disabled for security reasons. Anyone can register a name and so it would be unsafe to grant him op permissions upon registration

It is. We intentionally do not restore OP status of a player that has just registered.
That's regarding registration, though. After a normal login it should work

It‘s disabled for security reasons. Anyone can register a name and so it would be unsafe to grant him op permissions upon registration

I mean... can op restore their permission after registeration?
Or is it possible to check whether a player is op

It is. We intentionally do not restore OP status of a player that has just registered.
That's regarding registration, though. After a normal login it should work

Oh I know. if a non-op registered op's account, this is unsafe.
But it will be safe on a server with offline mode turned off.
I think you can detect whether the server is running in offline mode (is this implemented?)