Boot up mac in diagnostic mode

How to Use OS X Boot Options to Troubleshoot Your Mac

If you have a Mac notebook, double-check that the computer is connected to the power adapter to prevent it from shutting down during testing. Additionally, unplug all external devices, including USB thumb drives and external storage devices, from your Mac except the keyboard, mouse, display and Ethernet adapter.

Apple Diagnostics reference codes are explained in the last section. If you Mac is connected to the Internet via Ethernet or Wi-Fi and an issue has been detected, you will be offered to get support articles from Apple. Doing so will reboot your Mac in OS X Recovery Mode which will let you access your support and service options through Safari and see additional troubleshooting steps and information to help resolve your issue. You can use the following keyboard shortcuts to enter Apple Diagnostics or Apple Hardware Test and select its features. If Apple Diagnostics or Apple Hardware Test isolate a hardware issue with your computer, you will get an error code.

You will need this code to learn more about what might be wrong with your computer and how to troubleshoot the issue.

Let's begin the health checkup with a hardware diagnostic test. Keep holding the key until you get the option to select a language.


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With the arrow keys on your keyboard, navigate to the language you want and hit the return key. It's possible that you will first get asked to join a Wi-Fi network if the diagnostic image can't be pulled from the machine itself, but it should join known networks automatically. Once a language is selected, Apple Diagnostics will get to work. Testing will take 2 or 3 minutes and will present you with a "No issues found" message or a list of issues and reference codes. Similar to newer Mac models, AHT will also present to you a language selection window, but once a language is selected the test environment will load and not automatically run.

This includes any pre-Intel Mac and most Intel Macs until Apple Diagnostics or AHT is a good start, but the test is pretty basic. There are still plenty of hard drives out there, and as we all know, sooner or later those drives will fail. If you use hard drives, they may already be failing without you even noticing, so it's best to check up on these spinners once in a while. These utilities will both look at and interpret the S. It's important to keep in mind that interpreting S. A drive that's OK today may still crash completely tomorrow, but a good interpretation of the S.

I haven't had a hard drive fail in years. Still, some is better than none at all, so here's the first utility:. Rember : A small utility that gives you just a few controls. Rember is a graphical representation of the command line utility memtest and will give your RAM a proper workout with several different algorithms.

Another way to improve Mac performance

If an issue is present, Rember will likely find it. Depending on the amount of RAM you have and the speed of that RAM, Rember can take a very long time to run and if you've told it to test all the available RAM it can get its hands on, your Mac will be pretty much unusable for the duration of the tests.


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Make sure you quit as many applications as you can so that more RAM is available for testing. You may also want to loop the test a few times so that it can get its hands on different memory blocks in between tests. If all goes well, this will be the result:. To run this test, a bootable flash drive or CD must be created, and once booted from that source no slick user interface will be found. The interface you will get is text-based, ugly and a little intimidating, but this test is extremely powerful, so it's worth running anyway.

By booting from this external volume, little to no RAM is used, which means pretty much all of it is available for testing. With a range of algorithms, including one lovingly called the Hammer Test, memtest86 is the best possible option for RAM testing out there. The free version will be enough to give your RAM a good workout and expose any issues there may be. Here is memtest86 running the hammer test on a MacBook Pro:. By design, benchmark utilities include a range of algorithms to test the performance of a CPU.

Also, the resulting benchmark score can be an indication your hardware is not performing as it should. Geekbench is likely the most well known computer benchmark utility out there. Geekbench gives your CPU a good amount of data to crunch. Various algorithms test your CPU in different ways and the final score—which you can compare to other Macs with same or similar specs—tells you if it crunched all that data in the expected time frame. This is where your CPU is really pushed to its limit. The right stress tests put your CPU to work in ways that real world usage probably never will.

After all, we don't want a real world workload, we want the absolute max it can take to see if it fails. It is still used by computer repair shops and even the Genius Bar today. It's not a test that puts a CPU through its paces, but if anything it will test the cooling system and show you if it's able to keep the CPU from overheating.

The concept is simple: Give the CPU a command that evokes an affirmative "yes" response over and over and over. To kill the process, go back to the Terminal window and type " killall yes " without the quotes and hit enter.

Apple Diagnostics or Apple Hardware Test mode?

This puts only a single CPU core at work, so you want to repeat the command as often as you have cores, then again to hit the virtual cores. For a 4-core CPU that has 8-cores total with the virtual cores included, the command becomes:. To abort the test at any time, type " killall yes " followed by enter and quit Terminal. Chances of it failing such a simple test are slim, so if you want to step it up, try the following:. Prime95 was created to help find new Mersenne prime numbers, but so many people started using it to stress test their CPU's that the app's creators built a dedicated stress test into the app.

Called the "Torture Test," it certainly lives up to its name and taxes your CPU and subsystems to its maximum capabilities. Running the Torture Test for several hours hours recommended by the communities will prove, without a doubt, your CPU is either a number crunching monster with an endless appetite or ready for recycling heaven.

How to start up your Mac in Apple Diagnostics or Apple Hardware Test mode

Without it, you'd just be staring at a blank screen. Of course, games can't live without it; and, if you use any of the Adobe, Final Cut or other graphics intensive apps, then you most certainly need it. It runs hotter and consumes a lot more energy, so the chances of it failing are much greater.

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