How to Re-Install Mac

You may have a couple of reasons to consider re-installing Mac, namely your currently installed instance became unstable, the system files of your Mac got corrupted and aren’t repairable anymore, Disk Utility failed to repair the hard drive errors from within the operating system, etc.

Re-installation of Mac requires your computer to be connected to the Internet. This is important because the operating system (macOS High Sierra for this example) is downloaded from the Apple’s recovery server, and if there’s no Internet connection, you will be displayed with “The recovery server could not be contacted” error at the time of re-installation.

Note: Because the re-installation process may require complete erasure of your hard drive, it is important to back up your data using Time Machine or any other third-party backup tool of your choice before proceeding.

Once everything is in place, here’s how you can re-install Mac on your computer:
    Restart in Recovery Mode
    Click the Apple logo from the top-left corner, click Restart, click Restart again in the confirmation box, press and hold down the Command + R keys as your computer powers up again, and release the keys as soon as you see the Apple logo on the screen (and before the progress bar appears). This restarts your computer in Recovery Mode. From here you can repair any errors with hard disk, add, remove, or resize the partitions, restore data from a Time Machine backup, etc. If the current instance of Mac isn’t stable enough to boot your computer, you can power it on, and use the Command + R keys as explained in this step to get to Recovery Mode.

    Get to Disk Utility
    Click Disk Utility from the macOS Utilities box, and click Continue. This opens the Disk Utility window. From here you can manage all the hard disks and their respective partitions.

    Wipe off current Mac
    Select the partition your Mac is installed on (Main for this example), click Erase from the toolbar at the top, click Erase in the box that appears next, and click Done upon completion. This erases all the data from the partition, including your Mac. If your hard disk has some inconsistencies, you can click First Aid from the toolbar, and follow the on-screen instructions to repair the disk.

    Note: Before erasing the partition, optionally, you can rename it by typing a new name in the Name field. You can even change the partition type (not recommended if the computer worked fine earlier) by selecting your preferred file system (usually Mac OS Extended (Journaled)) from the Format drop-down list.
    Get back to macOS Utilities
    Click Close from the top-left corner of the Disk Utility window. This closes the window, and takes you back to the macOS Utilities box.

    Re-install Mac

Click Reinstall macOS, click Continue, and follow the on-screen instructions from there. This downloads a fresh copy of Mac from the Apple’s recovery server, and installs it on your computer. As mentioned earlier, make sure that your computer is connected to the Internet either via a Wi-Fi or Ethernet connection for smooth and uninterrupted re-installation.
Note: Your computer may restart multiple times during the re-installation process.

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