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Clarence
2018-07-11, 14:11
Hey there,


I recently created a bootable USB with Kali Linux loaded on it to be run on my Macs. I went about setting up persistence on the USB. However, despite the persistence seeming to work multiple times, it became apperent that I needed to run a few update and upgrade commands to get things working properly. Whilst the USB was plugged in and in the persistence desktop, I started the command "apt upgrade" which was taking hours but I left it to do what it needed to. Later, I came back to the iMac to find that it was frozen. I sat at the computer for a few minutes to see if anything would happen, then, all of a sudden the screen went black and a sort of static pattern appeared. The iMac then restarted and showed the Apple boot screen as normal with the exception that there were numerous vertical yellow lines across the screen. After a few minutes, this screen would then progress onto a blank white screen and stay like this for a few minutes then the system would automatically reboot and the cycle would start all over again. I have let the computer go through numerous cycles to no success. The computer repeats this cycle over an over.

Yellow bar screen:

3061


Blank white screen:

3062

After becoming rather frustrated, I tried the following:


Resetting the NVRAM (Resets but does nothing to help the issue)
Booting into safe mode (Doesn’t let me boot into safe mode)
Booting into recovery mode (Doesn’t let me boot into recovery mode)
Booting from a bootable flash drive with a fresh install of OSX loaded (Doesn’t get past opening the image before restarting)



After searching the internet, I found that many people had had similar problems but none of whom claimed that it was due to an issue with Kali Linux. Many people claimed that this issue was due to a dead GPU. However, I believe that the problem may be down to software as it was during an unsuccessful upgrade of Kali Linux that this problem started. Despite this, I tried all of the “fixes” that were mentioned in each of the posts with no success.


Following this, I contacted Apple Support directly and told them about the symptoms of my problem. They tried to be helpful by recommending many of the fixes I had tried such as resetting the NVRAM. However, as before, these fixes did not work. The last thing they recommended to try was taking it into an Apple Authorized service provider and hope to see if they could fix it as the age of my iMac meant that they couldn’t do anything about it in an Apple Store.


I am hesitant to take it into an Apple Authorized service provider for a few reasons including the extortionately high prices listed on their websites for problems like this, the possibility that any money spent would be a waste if the problem was not resolved by them and finally that they may not even have the correct hardware required for the fix if hardware is the problem.


Interestingly, I was successfully able to boot into the Fail-safe mode of Kali Linux from my USB (the lines still persisted even inside Kali) but was unaware of anything I could do inside Kali linux that may be able to fix the problem.


This is why I have come to this forum for help. I would be unbelievably grateful if anyone could suggest how I could move forward with this problem. I am aware that the Kali linux forum may not be the proper place to post an issue with an iMac boot but feel that due to the fact that I believe the problem was caused by Kali Linux and that I am able to boot into Kali Linux, I hope that someone may be able to point me in the right direction.


Here are some more specific technical details:


iMac model and components (all the base specifications from the website):
https://support.apple.com/kb/sp623?locale=en_GB




Expected behaviour:
iMac successfully boots into macOS, unaffected by any problems that Kali Linux may have had


Observed behaviour:
iMac stays in an unsuccessful “boot cycle”


Possible ideas:
Kali Linux may have had an error while loading some sort of graphics driver which has persisted onto my Mac boot causing it to stay in this cycle.
Kali Linux may have over strained the GPU (I don’t know why it would have) and caused a failure


As I said, I would be immensely grateful for any advice people could give me for my problem.

Thank you in advance for any help,
Kind regards

bigbiz
2018-07-15, 03:03
With no history with iMAC machines. Ill shoot into the dark, can you reset from bios, or maybe cmos reset. Connecting cmos battery leads to force reset. Maybe check google or youtube how to do it. I google it try to reset your PRAM.

broomdodger
2018-07-15, 11:02
If you have a wireless keyboard...
find a WIRED keyboard for the following.

Unplug ALL peripherals
Plug in ONLY a wired keyboard

Reset SMC for iMac
Shut the iMac down
Unplug the iMac from power
Wait 15 seconds with the iMac unplugged
Plug the power cord in and wait 5 seconds

Press the power button
Immediately hold down the COMMAND and letter S keys
Until you see a black screen with white letters

Did you get to a black screen with white text?

Do you still see vertical lines?
If yes, then it is a bad GPU.

Force quit the iMac:
Hold the power button until iMac shut down.

Clarence
2018-07-15, 20:16
With no history with iMAC machines. Ill shoot into the dark, can you reset from bios, or maybe cmos reset. Connecting cmos battery leads to force reset. Maybe check google or youtube how to do it. I google it try to reset your PRAM.

Thank you for your reply, I'll give that a go when my USB keyboard arrives. I've already tried resetting the PRAM but I hadn't thought about the BIOS or CMOS so I'll give that a go soon and report back onto the forum whether or not I've managed to solve the problem

Clarence
2018-07-15, 20:20
If you have a wireless keyboard...
find a WIRED keyboard for the following.

Unplug ALL peripherals
Plug in ONLY a wired keyboard

Reset SMC for iMac
Shut the iMac down
Unplug the iMac from power
Wait 15 seconds with the iMac unplugged
Plug the power cord in and wait 5 seconds

Press the power button
Immediately hold down the COMMAND and letter S keys
Until you see a black screen with white letters

Did you get to a black screen with white text?

Do you still see vertical lines?
If yes, then it is a bad GPU.

Force quit the iMac:
Hold the power button until iMac shut down.

I've now got a USB keyboard on order which should arrive relatively soon hopefully. I've already tried resetting the SMC but haven't been able to boot into single user mode as you have suggested due to the current keyboard situation. A solution I have found online which I am going to try if all else fails and I am able to boot into Single User mode is to bypass the GPU all together as mentioned in the link here (https://fleecehead.com/2015/04/18/apple-support-rocks/). Once again, I will report back onto the forum with any developments to the situation.

Thank you for your suggestions.

broomdodger
2018-07-15, 21:57
Sometimes... a wireless keyboard can start single user mode or safe-boot
Hold cmd+S BEFORE pressing the power button
What color is the iMac? silver or white

Clarence
2018-07-15, 22:06
Sometimes... a wireless keyboard can start single user mode or safe-boot
Hold cmd+S BEFORE pressing the power button
What color is the iMac? silver or white

I am aware that the wireless keyboard can sometimes work during the boot up process as a few days ago I was able to hole the Option key for booting options but this required numerous attempts and combinations of holding down the wireless keyboard power button then turning on the iMac etc. However, I have been unable to replicate this since but not to worry as I have a USB keyboard on the way. As you can see from the pictures I attached in my original post, the iMac is silver. By the way, I am starting to think that the problem is software related as you can see from the pictures that the Yellow lines only appear at one point of the boot up process and not all of it. When I boot up into single user mode using my USB keyboard, what are some of the commands you would advice running before I bypass my GPU all together?