I tried to start Odoo 11 directly in developer mode by using the arg --dev=all without having to pass by Settings then Activate the developer mode but it doesn't works. I've also a Warning about the Watchdog module which is missing but I can't find it in the module list. Does --dev=all is used for something else?
You can do like this if you notice what happen when you activate developer mode it's just adding this word to the url. debug=.
So just save a favorite link i don't remember exactly but it should be something like this.
server_ip:8069/web?debug=