Save yourself time and money by trying to fix it yourself. Read More to learn as much information about the problem as you can. To do so: Connect the external drive you want to use as a destination for your files.
If you have a firmware password set on your Mac, Single User mode is not available to you. However, in some cases, your Mac may find disk or file system problems and be unable to repair them when you perform the above steps.
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And when it does, apps can find themselves with free reign to alter files and modify read-only files which can cause all kinds of permission errors and system issues such as lagging, freezing, or crashing. If you interrupt the process while it is making changes to your drive, you may incur data loss.
By taking this step, Disk Utility will work through your hard drive to detect broken or misbehaving permissions and list them for repair. Why an older version? This boot mode allows you to make changes to shared user resources.