The OS X Menu bar is the gray strip across the top of your monitor, that holds the apple menu and system and application menus on the left, and the status menus (menu extras) on the right. This bar should be present and active to allow you to control your system and applications; however, there may be instances where it is not showing all the time.
If this occurs, you may see other problems like your screen suddenly shifting to the left or right when you move your cursor towards the edge.
There are several reasons why the system menu bar may be hidden from view:
- Full Screen Apps
If your are using an app that is set to full-screen mode, then the menu bar will be hidden by default. However, if you move your cursor to the top of the screen then the menu bar should appear to give you access to the application and system menus. To clear an app from full-screen view, you can try pressing Control-Command-F (though this sometimes does not work, depending on the app), or you can click the blue opposing arrows button in the menu bar when you place your cursor to the top of the screen to reveal it.
- Zoomed screen
As part of its Accessibility options, OS X includes a screen zooming feature where you can hold the Control key and scroll, or press designated hotkeys to increase the size of items proportionally on screen. If you are slightly zoomed in, then while you may still see most of your screen, the menu bar may be hidden. Therefore try holding the control key and scrolling up and down to see if this changes the zoom level, or disables it.
The use of the control key in this manner may require you to enable it, so if this shows no effect then go to the Accessibility system preferences, click the Zoom category, and check the appropriate options to toggle zooming on or off.
- Activate Mission Control
- Log out and back in
Finally, if the menu bar does not show up properly, try logging out and back into your system. If the background processes such as SystemUIServer that are responsible for managing the menu bar are hanging, then logging out and back in might help clear the hang and have them running properly. When you do this, the system may quit all services like the Dock and Finder, and only show a blank desktop background for a few minutes. Allow the system to stay like this and log out on its own, since at this point it is attempting to quit the hanging background processes. If you see no progress after about 10 or so minutes, then try resetting your system.