If you have a recent backup, erase your startup disk and reinstall macOS. Hold T to boot into Target Disk and access your data from a second Mac. Open Disk Utility and run First Aid on your startup disk. Bypass the Trash when you delete files with option+command+delete. Boot into Safe Mode by holding the shift key during startup. It’s tough to know where to start when you can’t even delete files anymore, but we’ve got you covered with these quick tips, explained in detail below: How to create space on your Mac when the startup disk is full. Erase your startup disk and reinstall macOS Repair your startup disk using Disk Utility How to delete files on your Mac when the startup disk is full. How do I find out how much free space I have on my startup disk?. How much free space do I need on my startup disk?.Why do I need free space on my Mac’s startup disk?.