Introduction to macOS Troubleshooting

macOS is known for its stability and user-friendliness, but like any operating system, it occasionally encounters problems. Whether you're facing a Mac that won't boot, applications that keep crashing, inexplicably slow performance, or stubborn network issues, understanding how to troubleshoot effectively saves time and potentially expensive repair bills.

This guide covers the most common macOS problems and their solutions, from basic fixes anyone can perform to advanced techniques for persistent issues. We'll work through problems systematically, starting with simple solutions before moving to more involved ones. Many issues that seem serious have straightforward fixes once you know where to look.

Before we begin, a word about backups: if your Mac is still bootable and you haven't backed up recently, do so now. Time Machine makes this easy, and many troubleshooting steps we'll cover become risk-free when you have a current backup. If your Mac won't boot normally, skip to the startup issues section first.

Startup and Boot Problems

A Mac that won't start normally is alarming, but often fixable. First, determine what happens when you press power. Nothing at all suggests a power issue: check the power cable, try a different outlet, or for laptops, try a different charger. If you hear the startup chime or see lights but nothing on screen, it could be a display issue—try connecting an external monitor.

If your Mac starts but gets stuck on the Apple logo or loading bar, boot into Safe Mode by holding Shift during startup (for Intel Macs) or holding the power button for 10 seconds, then selecting your disk with Shift held (for Apple Silicon). Safe Mode runs disk checks, clears caches, and loads only essential software. If Safe Mode works, the problem is likely a third-party extension or corrupted cache.

The Startup Disk full warning prevents normal boot on some systems. Boot into Recovery Mode (Command+R for Intel, or hold power button and select Options for Apple Silicon), open Disk Utility, and check space. If critically low, you can use Terminal in Recovery to delete large files. Common culprits include massive log files and old iOS backups.

NVRAM and SMC resets can fix various boot issues. For NVRAM, restart and hold Option+Command+P+R for 20 seconds (Intel Macs only—Apple Silicon doesn't need this). SMC resets vary by model; look up your specific Mac model for instructions as the process differs for desktop versus laptop and by year of manufacture.

Application Crashes and Freezes

Apps occasionally crash, but frequent crashes indicate a problem. Start by updating both macOS and the problematic app. Updates often include fixes for crashes. Check the App Store for updates, or if the app is from outside the store, check the developer's website.

Corrupted preferences can cause app instability. Preferences live in ~/Library/Preferences as .plist files. Quit the app, find its preference file (usually named like com.developer.appname.plist), move it to the Desktop, and restart the app. It will create new preferences. If this fixes the crash, you've found the problem. You'll need to reconfigure settings.

Application Support and Caches folders can also cause issues. ~/Library/Application Support/ contains app data, and ~/Library/Caches/ holds temporary files. Try moving the app's folders from these locations and restarting. Some apps behave differently when their data is gone—they might need to re-download content or rebuild databases.

For persistent crashes, Console.app provides detailed logs. Open it before replicating the crash, then look for entries from around the crash time. Error messages sometimes point directly to the cause. Developer forums often have solutions for specific error messages if you search for the exact text.

Performance Issues

A slow Mac is frustrating but often easily fixed. Start with Activity Monitor (in Applications > Utilities). Check CPU, Memory, and Disk tabs. Look for processes using excessive resources. Some apps leak memory over time; quitting and reopening them helps. If a process you don't recognize is using resources, search its name online before ending it.

Low disk space seriously impacts performance. Keep at least 10-15% of your disk free. Go to Apple Menu > About This Mac > Storage to see what's taking space. System Preferences > Storage has Recommendations for freeing space. Large culprits often include old iOS backups, unused applications, and forgotten downloads.

Startup items slow boot times and consume resources. Go to System Preferences > Users & Groups > Login Items. Remove anything you don't need starting automatically. Some apps add startup items without asking—check here after installing new software.

Spotlight indexing can cause temporary slowdowns, especially after major updates or adding new files. Activity Monitor will show mds and mdworker processes working hard. Let it finish—interrupting can cause repeated reindexing. If Spotlight seems stuck, you can rebuild the index from System Preferences > Spotlight > Privacy by adding then removing your hard drive.

Network and Connectivity Issues

Wi-Fi problems are common and often simple to fix. Start by toggling Wi-Fi off and on. If that doesn't work, remove the network from System Preferences > Network > Wi-Fi > Advanced and rejoin. This clears the stored connection details, which sometimes become corrupted.

DNS issues cause websites to not load even when connected. Try changing DNS servers in System Preferences > Network > Wi-Fi > Advanced > DNS. Remove existing servers and add 8.8.8.8 (Google) or 1.1.1.1 (Cloudflare). These public DNS servers are often faster and more reliable than ISP defaults.

The network configuration can become corrupted. Go to /Library/Preferences/SystemConfiguration/ and delete files named com.apple.airport.preferences.plist, NetworkInterfaces.plist, and preferences.plist. Restart your Mac—it will recreate these files. You'll need to re-enter Wi-Fi passwords.

Bluetooth problems often resolve with similar steps: toggle off and on, remove and re-pair devices. Sometimes it helps to delete Bluetooth preferences: remove com.apple.Bluetooth.plist from /Library/Preferences/ and restart. For persistent Bluetooth issues, especially after macOS updates, resetting the Bluetooth module helps: Option-click the Bluetooth menu bar icon and choose "Reset the Bluetooth module."

Storage and File System Problems

Disk errors can cause various issues. Disk Utility's First Aid should be your first stop. Boot into Recovery Mode, open Disk Utility, select your disk (not the volume), and run First Aid. This checks and repairs the file system. For serious problems, you may need to boot from Recovery to repair your main disk.

For files that won't delete—often because of permission issues or stubborn apps—try Terminal. The command "rm -rf /path/to/file" forces deletion. Be extremely careful with this command; it won't ask for confirmation and can delete important files if you specify the wrong path. Using the full path is safer than wildcards.

If your disk is encrypted with FileVault and you've forgotten the password, Recovery your Mac account password can unlock it if you set that option. Otherwise, your recovery key—which you should have saved during setup—is required. Without either, data recovery is effectively impossible, which is the point of encryption.

Hardware-Related Issues

Apple provides built-in diagnostics. For Intel Macs, hold D during startup. For Apple Silicon, hold the power button and select Options, then hold Command+D. The diagnostic runs tests and provides error codes. Search Apple's support site for specific codes—some indicate user-fixable issues while others require professional service.

Kernel panics (the Mac equivalent of Windows' Blue Screen) usually indicate hardware or driver issues. Note any error messages. Common causes include faulty RAM, failing drives, and incompatible kernel extensions. If you recently installed new hardware or software, remove or uninstall it. Third-party RAM that doesn't meet Apple's specifications often causes problems.

Battery issues on laptops such as short life, not charging, or swelling are common. Check battery health in About This Mac > System Report > Power. If Condition shows anything other than Normal, the battery should be replaced. Swelling batteries are a safety hazard—stop using the computer and get service immediately.

Preventive Maintenance

Regular maintenance prevents many problems. Keep macOS and apps updated—most updates include bug fixes and security patches. Use Time Machine for backups, ideally to an external drive that stays connected or a network drive. Check the backup occasionally to ensure it's working.

Periodically review System Preferences > Security & Privacy for privacy settings and enabled extensions. Remove anything you no longer need. Check Users & Groups > Login Items to prevent unnecessary startup programs. Less running in the background means better performance and fewer potential conflicts.

About once a year, consider a clean install if your Mac has accumulated years of software installations. Back up with Time Machine, erase the disk, install a fresh macOS, then migrate only the data you need. This clears out accumulated cruft and often makes an old Mac feel new again.