Don't Update If You're Jailbroken
If you're jailbroken and you want to keep your jailbreak, don't update to iOS 9 or iOS 9.0.1. There is no iOS 9 jailbreak, at least not yet.
While we expect developers to release one at some point in the future, it's not clear when a release will take place. It could be days, it could be months from now. For the moment, you'll need to stay put on iOS 8.4 or whatever you're on.