How to Format and Reinstall macOS Yosemite: A Comprehensive Guide

If your macOS Yosemite installation is running slow, experiencing frequent crashes, or you’re planning to sell or give away your Mac, a clean installation is often the best solution. This guide provides a detailed, step-by-step process for formatting your hard drive and reinstalling macOS Yosemite (10.10). **Before you begin, please understand that formatting your hard drive will erase all data. Back up everything important before proceeding!**

Why Reinstall macOS Yosemite?

There are several reasons why you might want to reinstall macOS Yosemite:

* **Improved Performance:** Over time, your Mac can accumulate junk files, conflicting software, and corrupted system files. A clean installation removes these issues, resulting in a faster and more responsive system.
* **Troubleshooting Issues:** Reinstalling the operating system can resolve persistent software glitches, application crashes, and other system-related problems.
* **Preparing for Sale or Giveaway:** A clean installation ensures that your personal data is completely removed, protecting your privacy.
* **Fresh Start:** Sometimes, you just want a fresh start with a clean operating system, free from any previous settings or applications.

Prerequisites

Before you begin the formatting and reinstallation process, make sure you have the following:

* **A Bootable macOS Yosemite Installer:** You’ll need a bootable USB drive containing the macOS Yosemite installer. If you don’t have one, you’ll need to create it. Instructions for creating this are detailed further below.
* **A Reliable Internet Connection:** You’ll need an internet connection to download the macOS Yosemite installer (if you don’t already have it) and potentially for activation or other post-installation steps.
* **An External Hard Drive or Cloud Storage for Backups:** This is **crucial**. Formatting your hard drive will erase everything. Use Time Machine or another backup method to safeguard your important files.
* **At Least 8GB USB Drive:** To create a bootable installer.
* **Sufficient Battery or Power Connection:** Ensure your Mac is plugged into a power source throughout the process to prevent interruptions.
* **Your Apple ID and Password:** You might need this to sign in to iCloud or the Mac App Store after the installation.

Step 1: Back Up Your Data (Crucial!)

This is the most important step. Formatting your hard drive will delete all data on it. Use Time Machine or another backup method to create a complete backup of your system.

**Using Time Machine:**

1. Connect an external hard drive to your Mac.
2. Open **System Preferences** from the Apple menu.
3. Click on **Time Machine**.
4. Select your external hard drive as the backup disk.
5. Enable the **Back Up Automatically** option.
6. Click **Back Up Now** to start the backup process. Wait for the backup to complete, which may take several hours depending on the amount of data.

**Alternative Backup Methods:**

If you don’t want to use Time Machine, you can manually copy your important files to an external hard drive or cloud storage service like iCloud Drive, Dropbox, Google Drive, or OneDrive. Make sure you back up all your documents, photos, videos, music, and any other important data.

Step 2: Download macOS Yosemite (If Needed)

If you don’t already have the macOS Yosemite installer, you’ll need to download it from the Mac App Store. This is not always straightforward, as Apple typically only offers the latest versions of macOS. Here’s how you might be able to download Yosemite:

* **Check the Mac App Store:** Search for “macOS Yosemite.” If it’s available, download it. Be aware that this is unlikely, as Apple tends to deprecate older versions. If you’ve previously downloaded it under your Apple ID, it *might* be in your purchase history.
* **Search Online Archives:** Some websites offer archived macOS installers. Be very cautious when downloading from these sources, as they may contain malware. Only download from reputable sites, and always scan the downloaded file with antivirus software before proceeding.
* **Use a Mac That Already Has Yosemite:** If you have access to another Mac running Yosemite, you can copy the installer from that machine.

**Important Considerations:**

* The downloaded installer will typically be found in your **Applications** folder. It will be named something like “Install OS X Yosemite.app.”
* Do not run the installer from within your current operating system. You’ll use it to create a bootable USB drive.
* Keep the installer application safe, as you might need it again in the future.

Step 3: Create a Bootable macOS Yosemite Installer

This is the most technical part of the process, but it’s essential for formatting and reinstalling macOS Yosemite. You’ll need a USB drive with at least 8GB of storage.

**Using Terminal (The Recommended Method):**

1. **Prepare the USB Drive:** Connect the USB drive to your Mac. Open **Disk Utility** (found in **/Applications/Utilities/**). Select the USB drive in the left sidebar. Click on the **Erase** tab. Give the drive a name (e.g., “YosemiteInstaller”) and select **Mac OS Extended (Journaled)** as the format. For Scheme, select **GUID Partition Map**. Click **Erase**.
2. **Open Terminal:** Open the **Terminal** application (found in **/Applications/Utilities/**).
3. **Use the `createinstallmedia` Command:** This command creates the bootable installer. The exact command depends on the name of your Yosemite installer application. Replace `YourVolumeName` with the name of your USB drive volume. Replace `/Applications/Install OS X Yosemite.app` with the actual path to the installer.

Here’s a general template:

bash
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia –volume /Volumes/YourVolumeName –applicationpath /Applications/Install\ OS\ X\ Yosemite.app –nointeraction

**Example (assuming your USB drive is named “YosemiteInstaller” and the installer is in /Applications):**

bash
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia –volume /Volumes/YosemiteInstaller –applicationpath /Applications/Install\ OS\ X\ Yosemite.app –nointeraction

4. **Enter Your Administrator Password:** Terminal will ask for your administrator password. Type it in and press Enter. Note that you won’t see any characters as you type your password.
5. **Wait for the Process to Complete:** The Terminal will display progress updates as it creates the bootable installer. This process can take 20-30 minutes or longer, depending on the speed of your USB drive. **Do not interrupt the process!** The last line should say something like “Install media now available at /Volumes/Install OS X Yosemite”.

**Important Notes:**

* The `createinstallmedia` command requires administrator privileges, which is why you need to use `sudo`.
* Double-check the paths to the installer application and the USB drive volume. Incorrect paths will result in an error.
* The `–nointeraction` flag tells the command to run without asking for confirmation.
* If you encounter errors, carefully review the command and the paths to ensure they are correct.
* If the process seems stuck, wait for a while. It can take a considerable amount of time.

Step 4: Boot from the USB Installer

Now that you have a bootable macOS Yosemite installer, you can use it to start your Mac in recovery mode and format the hard drive.

1. **Shut Down Your Mac:** Click on the Apple menu and select **Shut Down**.
2. **Insert the USB Installer:** Make sure the USB drive containing the macOS Yosemite installer is plugged into your Mac.
3. **Start Up in Recovery Mode:** Press the power button to turn on your Mac. Immediately press and hold the **Option (Alt)** key on your keyboard. Continue holding the Option key until you see the startup manager, which displays a list of bootable volumes.
4. **Select the USB Installer:** Use the arrow keys to select the USB drive you created (it should be labeled something like “Install OS X Yosemite” or the name you gave it). Press Enter to boot from the USB drive.

Step 5: Format Your Hard Drive

Once you’ve booted from the USB installer, you’ll see the macOS Utilities window.

1. **Open Disk Utility:** In the macOS Utilities window, select **Disk Utility** and click **Continue**.
2. **Select Your Hard Drive:** In the Disk Utility window, select your hard drive from the left sidebar. **Be absolutely sure you are selecting the correct drive. Selecting the wrong drive could erase other storage devices connected to your system.** It will likely be called “Macintosh HD” or something similar. If you have multiple drives, verify the size and partition information to ensure you select the correct one.
3. **Erase the Hard Drive:** Click on the **Erase** tab at the top of the Disk Utility window. Give the drive a name (e.g., “Macintosh HD”). Select **Mac OS Extended (Journaled)** as the format. For Scheme, select **GUID Partition Map**. **Important: Choosing the wrong format can cause issues. Always use ‘Mac OS Extended (Journaled)’ for Yosemite.** Click **Erase**.
4. **Confirm the Erase:** A warning message will appear, reminding you that erasing the drive will delete all data on it. Click **Erase** to confirm.
5. **Wait for the Erase Process to Complete:** The Disk Utility will erase the hard drive. This process may take a few minutes. Once it’s finished, click **Done**.
6. **Quit Disk Utility:** Close the Disk Utility window to return to the macOS Utilities window.

Step 6: Install macOS Yosemite

Now that your hard drive is formatted, you can install macOS Yosemite.

1. **Select “Install OS X”**: In the macOS Utilities window, select **”Install OS X”** and click **Continue**.
2. **Continue Through the Installer**: Follow the on-screen instructions. Click **Continue**, agree to the license agreement, and select the hard drive you just formatted (e.g., “Macintosh HD”) as the installation destination. Click **Install**.
3. **Wait for the Installation to Complete**: The installation process will take a significant amount of time, typically 30-60 minutes or longer, depending on the speed of your Mac and the USB drive. Your Mac will restart several times during the installation. **Do not interrupt the installation process!**
4. **Post-Installation Setup**: Once the installation is complete, your Mac will restart and display the setup assistant. Follow the on-screen instructions to set up your user account, configure your network settings, and sign in to iCloud or the Mac App Store.

Step 7: Restore Your Data

After you’ve reinstalled macOS Yosemite, you can restore your data from the backup you created earlier.

**Restoring from Time Machine:**

1. Connect the external hard drive containing your Time Machine backup to your Mac.
2. During the setup assistant, you’ll be asked if you want to transfer information to this Mac. Select **”From a Mac, Time Machine backup, or startup disk”**.
3. Select your Time Machine backup disk and choose the most recent backup.
4. Follow the on-screen instructions to restore your data. This process can take several hours, depending on the amount of data.

**Restoring from Other Backup Methods:**

If you used another backup method, such as manually copying files to an external hard drive or cloud storage, you can manually copy the files back to your Mac. Simply connect your storage device, and move the files to their desired locations.

Troubleshooting Common Issues

* **Mac Won’t Boot from USB:** Make sure the USB drive is properly formatted and that the `createinstallmedia` command was executed correctly. Also, ensure that you’re holding down the Option key correctly during startup.
* **Installation Stuck:** Ensure your Mac has sufficient power and a stable internet connection (if required). If the installation seems stuck for an extended period, try restarting your Mac and attempting the installation again.
* **Disk Utility Errors:** If you encounter errors in Disk Utility, try running First Aid on the hard drive. If that doesn’t work, you may need to try a different formatting option or consider the possibility of a hardware issue.
* **Forgot Apple ID Password:** If you forgot your Apple ID password, you can reset it on Apple’s website.
* **No Internet Connection:** Ensure that your Wi-Fi or Ethernet connection is working properly. Try restarting your router or modem.
* **Installer is Damaged or Incomplete:** Try re-downloading the Yosemite installer. If you suspect the download source is unreliable, find a different (reputable) source.

Alternatives to Reinstalling Yosemite

Before resorting to a full reinstall, consider these alternatives:

* **Safe Mode:** Booting into Safe Mode (hold down the Shift key during startup) disables certain software and drivers, which can help identify the cause of problems.
* **Disk Utility’s First Aid:** Running First Aid in Disk Utility can repair minor disk errors.
* **Uninstall Unnecessary Applications:** Remove any applications you no longer use, especially those that might be causing conflicts.
* **Reset PRAM/NVRAM:** Resetting PRAM/NVRAM can resolve certain hardware-related issues. To do this, shut down your Mac, then turn it on and immediately press and hold the Option, Command, P, and R keys together. Release the keys after about 20 seconds, during which time the Mac may appear to restart.
* **Run Apple Diagnostics:** Apple Diagnostics (formerly Apple Hardware Test) can help identify hardware problems. To use it, disconnect all external devices except the display, keyboard, mouse, and power adapter. Then, shut down your Mac, turn it on, and immediately press and hold the D key. Follow the on-screen instructions.

Conclusion

Reinstalling macOS Yosemite can be a time-consuming process, but it’s often the most effective way to resolve performance issues and prepare your Mac for sale or giveaway. By following the steps outlined in this guide, you can successfully format your hard drive and reinstall macOS Yosemite, restoring your Mac to its optimal performance. Remember to always back up your data before formatting your hard drive, and be patient during the installation process.

**Disclaimer:** This guide is for informational purposes only. The author is not responsible for any data loss or damage that may occur during the formatting and reinstallation process. Always proceed with caution and at your own risk.