If you did file operations inside a shell or for example using Nautilus, it can take quite a while until RubyMine takes note of them and updates things like your project tree or its internal file list.

Flushing file system buffers helps you out (run it from a terminal):
sync

This is also possibly via the RubyMine menus: File → Synchronize.

Note that you should disable the Java plug-in in your browsers after installation.

Ubuntu >= 12.04

Java 11

sudo apt install openjdk-11-jre-headless

Java 10

sudo add-apt-repository ppa:linuxuprising/java
sudo apt-get update
sudo apt-get install oracle-java10-installer

Java 8

You probably want to get rid of OpenJDK (which is installed by default and leads to bad RubyMine performance):

...

Since RubyMine 3.1 you can drag tabs across panes/windows and out of the main window to create new windows.

For any version below 3.1 do it like this (will only allow dragging tabs inside their pane, not across panes):

1. File → Settings
2. Editor → Editor Tabs
3. Check "Show tabs in single row"

Seriously.

This is an awesome gadget in your toolbox, even if your test coverage is great.

• gem install ruby-debug (Ruby 1.8) or gem install debugger (Ruby 1.9)
• Start your server with script/server --debugger
• Set a breakpoint by invoking debugger anywhere in your code
• Open your application in the browser and run the code path that crosses the breakpoint
• Once you reach the breakpoint, the page loading will seem to "hang".
• Switch to the shell you started the server with. That shell will be running an irb session where you can step thr...