IMPORTANT: When you first see your bootable devices show up, you may not see all of them immediately. If you press and hold the Control key during this step, your selection is saved in Startup Disk preferences, so it persists until you change it. Select your startup disk, then click the arrow under its icon, or press Return.If your Mac is protected by a firmware password, you can release the key when you’re asked to enter the password. Release the Option key when you see the Startup Manager window.Press and hold the Option key immediately after turning on or restarting your Mac.You should use the Startup Manager as described here: I pressed the power button to start my MacBook Pro, used the Startup Manager to select my macOS Mojave 10.14 beta 4 startup disk so an arrow appeared pointing to that bootable Mojave startup drive, clicked on the arrow, and macOS booted up perfectly. When I saw the prohibitory symbol, I held down the power button until the Mac shut down. Prohibitory symbol displayed when booting into macOS Mojave 10.14 beta 4 I was able to solve both my boot problem and update problem with simple solutions. Several Apple forums advise booting from a recovery hard drive, reinstalling macOS, repairing your hard drive with Disk Utility… These are all valid solutions… ones you should only use after trying something simple first. Apple says you should “try reinstalling macOS using macOS recovery.” Another Apple support page suggests that you “revert to a previous version of macOS if you experience trouble after installing an update” (using Time Machine).

Please don’t go through any lengthy reinstalls or plunge down the troubleshooting rabbit hole before you hear me out. When you see the prohibitory symbol, please don’t panic. Of course, we’re talking about products like the Mac Pro, Mac mini, iMac, MacBook, MacBook Air, and MacBook Pro. The is one of the symbols that users of Apple products running macOS rightfully fear. Here’s what my MacBook Pro’s screen showed me: Over the last week, I encountered the dreaded Apple “prohibitory symbol” - do not enter sign or stop sign - twice: once when just booting into macOS Mojave 10.14 beta 4 and again when updating to macOS Mojave 10.14 beta 8. SEE RELATED: The fix to Mojave slowing down to a crawl and freezing.

Macbook pro boots into os x utilities