I need to install macOS high sierra but i need to know the data will be erased or not and what is the way to install it without lose data.

  • 1
    The one sure way to ensure you don't lose data during an upgrade is to do a backup of your data before performing the upgrade. – Allan Jul 24 '18 at 19:58
  • Now i don't have any external device to backup data so i asked the question – Eman Rezk Jul 24 '18 at 20:00
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    Get one. They are very inexpensive and if something happens, it will be the cheapest insurance policy you will ever buy – Allan Jul 24 '18 at 20:14
  • Possible duplicate of Does upgrading Yosemite risk losing material on HD? – user151019 Jul 24 '18 at 22:11
  • To put this into context, this question was just asked today: Update macbook air to High Sierra frozen?. This is exactly why you need a backup. – Allan Jul 25 '18 at 11:28

Generally speaking, your can "upgrade in place" meaning High Sierra will install, upgrading your old version of macOS while keeping your data intact.

However, you should back up your data. This is the very first thing Apple says to do after checking that the upgrade is compatible with your machine.

Make Sure You're Ready to Upgrade

Before you upgrade, we recommend that you back up your Mac. Then, if your Mac is running OS X Mountain Lion 10.8 or later, you can upgrade directly to macOS High Sierra.

Upgrades should go without issue, but things happen. For example, the upgrade could be interrupted for any reason beyond your control thus, compromising your data.

Additionally, High Sierra will convert your HFS+ file system to APFS on the fly meaning you're converting file system that "holds" your data. This introduces another level of complexity increasing the chance for failure.

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