How do I always show (or autohide) menu items in Unity?

16.04 and later (Unity 7)

In addition to the gsettings option introduced in 15.04 (below), this same capability has been added to the Settings - Appearances window (click the gear icon top-right of the screen)

14.04, 15.04, 15.10

15.04 now has the ability to toggle the global menu as well as the local integrated menus (Via System Settings - Appearance - Behaviour tab) to be permanently on or off.

If you are running a fully up-to-date version of 14.04, this same ability has been backported.

To switch on permanently:

gsettings set com.canonical.Unity always-show-menus true

To switch off i.e. to autohide:

gsettings set com.canonical.Unity always-show-menus false

Go to Ubuntu software centre and download a tool named Unity tweak tool

If it's downloaded, launch it and choose Window controls menu from there. In there, click on show menu button, and close the tweak program. Reopen all windows and it should be working.

Also, please let me know if it did not work!