How to Boot Mac in Safe Mode

When you start your Mac in Safe Mode, macOS loads only the kernel extensions required by Apple for basic operation. Third-party kernel extensions, login items, and non-essential System Extensions are all skipped. This creates a clean environment where the only software running is what Apple ships with macOS.

During the Safe Mode boot process, macOS also performs a directory check on the startup volume, similar to running First Aid in Disk Utility. If the system detects directory issues, it attempts to repair them automatically before completing the startup sequence.

System caches, including font caches and kernel caches, are deleted and rebuilt during a Safe Mode boot. This is particularly useful when corrupted cache files cause display glitches, font rendering problems, or unexpected slowdowns. After restarting normally, macOS rebuilds these caches from scratch.

Start by shutting down your Mac completely. Use the Apple menu and choose Shut Down. Wait until the screen goes dark and all indicator lights turn off. Do not simply close the lid or put the Mac to sleep.

Press and hold the power button on your Mac. Continue holding it until you see "Loading startup options" appear on the screen. This typically takes about 10 seconds. The startup options screen displays your available startup disks along with an Options gear icon.

Select your startup disk (usually named "Macintosh HD"). Before clicking Continue, press and hold the Shift key on your keyboard. The Continue button changes to read "Continue in Safe Mode." Click it while still holding Shift. Your Mac will restart and boot into Safe Mode. You will see "Safe Boot" in the menu bar once the login screen appears.

Click the Apple menu and choose Restart. As soon as you hear the startup chime (or as soon as the screen goes blank on models without a chime), press and hold the Shift key. Keep the key held down throughout the entire boot process.

The boot will take longer than normal. This is expected because macOS is running a disk check and clearing caches while starting up. Do not release the Shift key early, even if the progress bar appears to stall. On older Macs with mechanical hard drives, a Safe Mode boot can take several minutes.

When the login window appears, look for "Safe Boot" displayed in red text in the upper right corner of the screen. If you see it, you have successfully entered Safe Mode. Log in with your password. Note that FileVault users may need to log in twice: once to unlock the disk and once to reach the desktop.

Login items and launch agents: All items configured to open at login are skipped. This includes applications you added in System Settings > General > Login Items, as well as launch agents and launch daemons installed by third-party software. If a problem disappears in Safe Mode, one of these items is likely the cause.

Non-essential system extensions: Only kernel extensions required by macOS are loaded. Third-party drivers for audio interfaces, graphics tablets, VPN clients, and other peripherals will not function in Safe Mode. This isolation helps determine whether a driver conflict is causing system instability.

User-installed fonts: Fonts not located in /System/Library/Fonts are unavailable. Applications may display text in substitute fonts while in Safe Mode. If a font-related crash stops occurring in Safe Mode, a corrupted font file is the likely cause.

Caches: macOS deletes font caches, kernel caches, and other system caches during a Safe Mode boot. These are rebuilt automatically when you restart normally. Clearing corrupted caches resolves a wide range of display, performance, and stability issues without requiring any manual intervention.

Safe Mode confirms whether a problem is caused by third-party software, but it does not tell you which specific item is the culprit. After restarting normally, you need a way to watch resource usage as each login item loads. MoniThor displays real-time CPU, memory, and disk metrics directly in the menu bar, making it easy to spot the process that spikes resource usage immediately after login.

If your Mac runs smoothly in Safe Mode but becomes sluggish after a normal boot, the cause is almost certainly a login item or launch agent. MoniThor shows per-process resource consumption so you can identify the exact application consuming excessive CPU or memory. Once identified, you can remove it from your startup items to resolve the issue permanently.

Comparing baseline metrics between Safe Mode and normal operation also reveals the cumulative resource cost of your login items. Some users discover that their startup software collectively consumes several gigabytes of RAM before they even open an application. MoniThor makes this overhead visible at a glance.

Startup failures: If your Mac gets stuck on the Apple logo, shows a progress bar that never completes, or repeatedly restarts during boot, Safe Mode bypasses the software most likely causing the failure. Once in Safe Mode, you can uninstall recently added software or remove problematic login items.

Testing third-party software conflicts: When your Mac experiences kernel panics, application crashes, or general instability, Safe Mode isolates whether third-party software is the cause. If the problem disappears in Safe Mode, you know a login item, system extension, or launch agent is responsible. Reintroduce items one at a time after a normal restart to identify the specific culprit.

Clearing corrupted caches: Garbled text, missing fonts, graphical artifacts, or a Mac running slow without obvious cause can result from corrupted cache files. A single Safe Mode boot and normal restart forces macOS to rebuild all caches, often resolving these issues without any additional troubleshooting.

Before major troubleshooting steps: Safe Mode is a lightweight first step. Try it before resetting the SMC, reinstalling macOS, or erasing your disk. Many issues that appear to be hardware or operating system problems turn out to be caused by third-party software that Safe Mode disables.