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If you try to defragment your boot disk, iDefrag will offer to reboot your computer into a special mode so that it can directly access the boot disk. Assuming you have the correct version for your machine, this will normally work reliably and there won’t be any problems, but we have had reports, particularly since the release of OS X 10.10, that some machines “get stuck” and just show a progress bar instead of booting fully.
If this happens to you, don’t panic! You don’t need to reinstall the macOS, or do anything drastic to your machine.
To recover from a stuck boot, simply hold the power button on your machine for five seconds until the machine shuts down. Then press the power button to turn the machine back on. The machine should boot normally.
If you continue to have problems, or if the machine fails to boot normally, please restart your Mac in verbose mode by holding ⌘V when you hear the boot chime1. You will see a lot of white text scrolling up the screen; if possible, we recommend that you record this with a video camera or mobile phone (obviously it’s only worth doing this if you can get the text into focus), then upload it somewhere (e.g. Dropbox) and send it to us. At least it should be possible to spot any error messages that appear, and hopefully to understand the cause of the problem.
One other thing worth trying is removing other third-party utility software, particularly anything that installs launch agents or startup items (in
/Library/StartupItems respectively), or anything that installs kernel extensions (typically in
/Library/Extensions but some older software installs things into
/System/Library/Extensions instead). If you do find that removing or disabling some third-party software fixes this problem, please let us know — at the very least we’ll be able to tell other customers about it, and ideally we’ll be able to find a workaround that doesn’t involve removing or disabling the other product.
If you prefer, you can set your machine to boot in verbose mode from Terminal by entering
sudo nvram boot-args=-v; to undo this, use
sudo nvram -d boot-args. ↩
Posted by alastair at 2017-May-22 14:05:34 UTC. Last updated 2017-Jul-19 14:07:35 UTC.