How to Fix common Apple Mac OS X problems

How to fix a Apple Mac

How to Fix common Apple Mac OS X problems

In general, the problems you run into on a Mac are reasonably universal across all versions of OS X Often you can do a lot of the troubleshooting yourself.

Repairing disks and running First Aid

Running Mac Disk Utility First Aid

Disk Utility has had a makeover in the later OS X releases and as a result the way that you repair a disk has changed slightly.
  1. Open Disk Utility (in Applications > Utilities, or cmd+space Disk Utility).
  2. Select the volume you wish to run First Aid on. This could be a external hard drive (if it’s your own Mac hard drive you will need to jump to the next section).
  3. Click on First Aid.
  4. Click Run. This will start the verification and repair process.
  5. When Disk Utility has run it checks you will see a drop-down sheet showing the status. You can click on the triangle at the bottom to see more information.
  6. If no errors were found you will see a green tick at the top of the drop-down sheet.
  7. If there were errors Disk Utility will attempt to repair them. (In older versions you had to manually choose Repair Disk).
Notes: Beginning with OS X El Capitan, system file permissions are automatically protected. It's no longer necessary to verify or repair permissions with Disk Utility.
You can use Disk Utility’s First Aid on your Mac’s startup drive. However, in order for First Aid to perform any repairs, the selected volume must first be unmounted. Your Mac’s startup drive can’t be unmounted since it's in use, which means you will have to start up your Mac from another bootable device. This can be any drive that has a bootable copy of OS X installed; alternatively, you can use the Recovery HD volume
If Disk Utility is unable to repair the drive, or it believes that the disk is about to fail it will warn you. Should this be the case you should back up your data before it’s too late.

Start in Safe Mode - Press Shift During Startup

Mac staring in Safe Mode

OS X includes a boot option called Safe Mode. Start up your machine while holding down the Shift key to have OS X only load required kernel extensions and login items. It will disable all non system fonts, all startup items, and login items.

This Safe Mode feature is a great way to troubleshoot OS X applications and extensions that aren’t working properly. If you are having OS X boot problems, always try this first to check and see if you have a rogue piece of software preventing your Mac from booting properly.

The mode also performs a check of your startup disk so it should be able to alert you to problems.
After shutting down your Mac wait 10 seconds and then press the power button. As soon as your Mac starts (you may hear a start up chime) press and keep holding the Shift key. Once you see the Apple logo you can stop pressing Shift.

Start in Recovery Mode - Press cmd+R During Startup

Max OS X Utilities Option

Since Lion OS X, when Mac OS is installed on a Mac a Recovery HD volume is created on your Start Up drive. This volume (which is normally hidden) can be used to boot from if you need to do things like repair the startup disk, reinstall Mac OS and more.
To restart in the Recovery HD you just need to press and hold cmd+R when you start up your Mac and keep holding those keys until the Apple logo appears. It can take a while to finish booting up. Once it has you will see a desktop with a window containing Utilities open.

Once you have run though these steps you should have a clearer idea about the nature of your issue. Read on to find out how to fix it.

Boot from a CD/DVD - Press C During Startup

Booting from a DVD Media MAC OS X

 If you hold down the C key on your keyboard you can boot from a CD / DVD or other bootable discs on your Mac.

Run the Apple Diagnostic utility - Press D During Startup

Apple Diagnostic Test utility

With the introduction of Intel-based Macs, Apple has built a built a  Apple Hardware Test utility into the Mac. Simply hold down the D key while starting up your Mac to boot into the Apple Hardware Test.

Reset and clear the PRAM - Press Option + Command + P + R

Sometimes on a Mac, the PRAM (parameter RAM) and NVRAM (non-volatile RAM) can become corrupt and cause various problems. These two memory areas store settings and information that is not cleared whenever you turn off your Mac’s power.

To do this, you’ll want to turn off your Mac, and then turn it back on while holding down the Command + Option + P + R keys.
Hold the keys down until the computer restarts and you hear the startup sound for the second time. Release the keys after you hear the second startup chime. The PRAM will be reset.

Boot from other Devices - Press Option During Startup

Max OS X Boot from other Devices

Holding down the Option key during startup will show you a boot screen with all bootable devices listed. You can use the mouse or the keyboard to select a device to boot into.

This is great for those times when your main installation of OS X isn’t working correctly and you need to boot into a bootable mirror of your OS X install.

Stuck Disc - Press Eject, F12, or Hold Down Mouse/Trackpad Button

Sometimes discs can get stuck in your optical drive. When you cannot seem to get them out, you may panic, but just try restarting while holding down either the Eject key, F12 key, or your mouse or track-pad button. Your disc will be ejected in a flash after doing this.

NetBoot - Press N During Startup

Mac OS X Network Boot (NetBoot)
If your setup includes a compatible network server (NetBoot), you can hold down the N key during startup to attempt a network boot. You can optionally use the Option + N keys during startup to start from a NetBoot server using the default boot image provided.

Target Disk Mode - Press T During Startup

Mac OS X Target Disk Mode - use as external disk to another Mac

Target Disk Mode is a great way to retrieve your files from your Mac if your machine refuses to boot properly. Sometimes it’s best to just retrieve those files and start fresh with a clean copy of OS X.
Target disk mode lets you share files between two Mac computers that are connected via their FireWire, Thunderbolt 2, USB-C, or Thunderbolt 3 (USB-C) ports. With target disk mode, one Mac appears as an external disk on the other Mac, allowing you to browse and copy files. This is useful when you need high transfer speeds or if the display on one of your computers isn't working and you need to get files from it.

How to set up and use target disk mode

To get started, connect your two Mac computers with a FireWire, Thunderbolt, or USB-C cable that supports sufficient data transfer speeds. Then follow these steps:
  1. If the Mac that you'll use as a disk is off, start it up while holding down the T key and skip to step four. If it's on, click the Apple menu and choose System Preferences.
  2. Click Startup Disk and then click Target Disk Mode. If you see a closed lock at the lower left, click it and type your password to make the Target Disk Mode button available.
  3. A message asks "Are you sure you want to restart your computer in target disk mode?" Click Restart.
  4. After the Mac starts up in target disk mode, it appears as a disk icon on the desktop of the other Mac. Double-click the disk to open it and browse its files.
  5. Transfer files by dragging them to or from the disk.
  6. Eject the disk by dragging its icon to the Trash (the Trash icon changes to an Eject icon).
  7. To exit target disk mode, press and hold the power button on the Mac you used as a disk. Then disconnect the cable.

Verbose Mode - Press Command + V During Startup

Mac OS X boot in Verbose Mode


Command + V boots your Mac into what is called Verbose Mode. Using this key combination will cause your Mac to become very verbose on startup and will show a terminal-like interface while booting. It will contain information important to startup, allowing you to diagnose startup problems by seeing any errors that may be occurring during startup. Verbose mode exits automatically when the computer's startup process progresses sufficiently and the blue screen appears.

Single User Mode - Press Command + S During Startup

Mac OS X boot in Single User Mode

 Holding down Command + S during startup will boot your Mac into Single User Mode. This is a terminal interface that allows you to login and interact with your computer via text input only. No graphical interface will be loaded. This mode is good for when you need to troubleshoot a startup issue, or modify a file or application that is preventing proper startup.

Mac is running slow

If your Mac is running slowly don’t download a program that claims it will speed up your Mac, the first thing you need to do is to try and find out what is causing the slowdown. Follow these steps to find out.
There are a couple of things you can look at in Activity Monitor. Open Activity Monitor (in Applications > Utilities > Activity Monitor, or by clicking cmd+space and typing Activity Monitor).
There are five different tabs along the top: CPU, Memory, Energy, Disk and Network.

To find out if something is hogging the power or memory click on Memory.

The resulting window displays a list of all processes running on your Mac, as well as a graph of memory usage. If it's green, all is good with your system (although you may still benefit from closing a few memory hogs so read on).
If it's amber or red, Mac OS is having trouble managing memory and could be the reason that your Mac is running slowly. This could be due to a memory-hogging application. To find out which apps or processes are misbehaving, organise the list by memory usage (arrow pointing down), and you can identify the culprit.

Make sure you ignore processes that have "root" listed as the user column, and focus on applications running from your user account. Don't quit 'root' processes.

If an application is using more memory than other applications you can close it by selecting the app and closing it from its menu, or by clicking on it in Activity Monitor and then clicking on the X icon at the top left of the menu.
In the block at the bottom of the table you can check how much memory (RAM) you have and how much memory is being used.

An app may also be causing issues if it is hogging a lot of CPU.

Click on the CPU tab and you'll see information similar to that in the Memory tab. The graph at the bottom shows user (in blue) and system (in red) CPU usage.

If you see an application which is using a significant chunk of CPU cycles, quit it and you should notice a performance improvement in your Mac.

Mac with a flashing question mark

If you started up your Mac and were greeted with a folder with a question mark in the middle it might mean that your Mac’s disk has failed. But before you panic, there may be another explanation, and you may be able to fix it.
That folder with a question mark inside indicates that your Mac can’t find the startup disk and therefore can’t boot. Fixing this issue will involve putting your Mac into Recovery Mode and choosing the correct startup disk (which is likely to be your Macintosh HD, unless you want to boot from an external drive).
However if you aren’t seeing your startup disk, or you can’t select it, it may If it’s necessary to repair your disk. To do so you can use Disk Utility - Applications > Utilities > Disk Utility (or click cmd+space and start typing Disk Utility).

Mac is frozen

If your problem is that your Mac has frozen in the middle of a task, or an app has become unresponsive, it is possible to Force Quit it by right clicking/control clicking on its icon in the Dock and choosing Force Quit.
Alternatively you can Force Quit an app by pressing Command+Alt+Escape at the same time.
You can also press command+ctl+eject on your Mac laptop to force reboot. Or hold down the power button to achieve the same thing.
Be aware that if you have to Force Quit or reboot your Mac you may lose some data. If you have a Time Machine back up you may be able to recover the date from that.

Mac OS X Kernel Panics

Mac OS X having a Kernel Panic

Since the majority of the time a kernel panic is transitory, it is tempting to just restart your Mac and get back to work.

I suggest doing the following.

Restart Using Safe Boot
  • During a Safe Boot (start with Shift Key), your Mac does a basic check of the startup drives directory structure. If everything is okay, the OS loads the bare minimum number of kernel extensions it needs to run. This means no startup or login items are run, all fonts except those used by the system are disabled, and the dynamic loader cache is dumped.
  • If your Mac starts up fine in Safe Boot mode, then the basic underlying hardware of the Mac is functioning, as are most system files. You should now try starting your Mac normally (simply restart your Mac). If your Mac restarts without any problems, then it may be a device software issue between apps and hardware. If the kernel panic doesn't reoccur in a short time, say a day or two of use, you can consider the problem a minor inconvenience and get on with using your Mac.
  • If your Mac won't start up after restarting from Safe Boot mode, then there is a likely problem with a startup or login item, a corrupt font or font conflict, a hardware issue, a corrupt system file, or a driver/hardware issue.