Reboot your Mac to see if it was an open program or app stopping the drive from being detected.Try a different wall outlet if there is one nearby.Change the hard drive power cable if you have a spare.Check the condition of the cable and swap it if you have a spare.Check that the external hard drive has power if it needs it.Check that the cable from the hard drive to your Mac is connected properly.After all, no one wants to waste half a day because they didn’t realize something just wasn’t plugged in properly. Get into the habit of doing this with any computer issues, as it can save time, money, and hassle in the long run. Troubleshooting an External Drive with a Mac First, we will check the basics, and from there, we make sure that macOS is set up to display external drives, can mount the drive, and that the drive has no errors on either the disk itself or its file structure. To view the contents of a folder at any time, you can use the ls command below.If your external drive still doesn’t appear, we have a couple of simple troubleshooting tips to fix an external hard drive not showing up on Mac.For example, a complete command includes the source and destination and looks like this: cp -R /Volumes/Macintosh\ HD/Users/Bob/Documents /Volumes/External\ Drive/ You’ll notice that any spaces also require a backslash in the command line. Type the cp -R Terminal command below and press Enter to copy a specified file or folder.Launch Disk Utility, mount your startup volume, if necessary, and close the app.Boot to macOS Recovery using the method appropriate to your Mac model.
Here’s how to use Terminal to copy files from a Mac that won’t boot: All you’ll need is a correctly formatted external disk connected to your Mac. If you’re comfortable with Terminal, you can use commands in macOS Recovery mode to copy files across to an external hard drive.