Bruneti ZM
Level 1 (0 points)

Q: Can't boot OS, gray screen and then GRUB prompt

Hello everybody! I need some help!!! I was formatting disk to do a clean Mavericks installation, when I reboot i tried to install from internet but suddenly my computer turned off and when I try to continue with the installation process I can't!

The computer starts with the grey screen but finally I've got a grub prompt screen (perhaps because i had ubuntu installed in the past).

The big problem is that I can't boot from USB, can't init a special mode to boot (command +s, option or others combinations doesn't works)

What can I do to fix it?

Can I boot from a DVD???

Please a need some help!!!!

iMac, OS X Mavericks (10.9.5)

Posted on Oct 10, 2014 4:46 AM

by Drew Reece,Solvedanswer
Drew Reece Drew Reece
Level 5 (7,490 points)
Notebooks
A:

Do you have a second Mac?

 

If recovery mode is failing you will need to erase the HD which will remove the data on disk. Do you have a backup of the disk? You would need second Mac or a bootable USB stick to access the internal disk.

 

I suspect you have GRUB installed into a MBR (via a GPT hybrid partition table) or possibly into the EFI partition (if it was a newer Linux). It could also be installed on another disk, so remove any external disks when you are testing. You will want to erase the entire disk to get rid of the MBR, Disk Utility should give you info about how the disk is setup. Internet recovery mode should allow the disk to be reformatted.

 

Many of the startup shortcuts won't work if the OS is damaged, safe mode & single user mode will fail, but target disk mode should work - How to use and troubleshoot FireWire target disk mode).

 

You can also boot a Linux live CD if you have one around. Certain Linux distros will read HFS+ volumes (but not write), if the disk is in a working state.

Posted on Oct 10, 2014 2:22 PM

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Bruneti ZM

Q: Can't boot OS, gray screen and then GRUB prompt

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  • Helpful answers

  • by Eric Root,

    Eric Root Eric Root Oct 10, 2014 1:53 PM in response to Bruneti ZM
    Level 9 (70,141 points)
    iTunes
    Oct 10, 2014 1:53 PM in response to Bruneti ZM

    If you have a DVD that came with the computer, try booting from it.

  • by Drew Reece,Solvedanswer

    Drew Reece Drew Reece Oct 10, 2014 2:22 PM in response to Bruneti ZM
    Level 5 (7,490 points)
    Notebooks
    Oct 10, 2014 2:22 PM in response to Bruneti ZM

    Do you have a second Mac?

     

    If recovery mode is failing you will need to erase the HD which will remove the data on disk. Do you have a backup of the disk? You would need second Mac or a bootable USB stick to access the internal disk.

     

    I suspect you have GRUB installed into a MBR (via a GPT hybrid partition table) or possibly into the EFI partition (if it was a newer Linux). It could also be installed on another disk, so remove any external disks when you are testing. You will want to erase the entire disk to get rid of the MBR, Disk Utility should give you info about how the disk is setup. Internet recovery mode should allow the disk to be reformatted.

     

    Many of the startup shortcuts won't work if the OS is damaged, safe mode & single user mode will fail, but target disk mode should work - How to use and troubleshoot FireWire target disk mode).

     

    You can also boot a Linux live CD if you have one around. Certain Linux distros will read HFS+ volumes (but not write), if the disk is in a working state.

  • by Bruneti ZM,

    Bruneti ZM Bruneti ZM Oct 10, 2014 2:39 PM in response to Drew Reece
    Level 1 (0 points)
    Oct 10, 2014 2:39 PM in response to Drew Reece

    This will be my next step to recover....but i tried again to reset pram and its works!!! The iMac restarts and show me the apple logo and start the net installation, thanks everybody for the help and tricks, cheers!

  • by samuelcarreira,

    samuelcarreira samuelcarreira May 20, 2016 4:02 AM in response to Bruneti ZM
    Level 1 (8 points)
    iPhone
    May 20, 2016 4:02 AM in response to Bruneti ZM

    My story (can be useful to someone with the same problem):

    I’ve installed Ubuntu on external USB 3.0 hard drive on an iMac late 2013. I created the following partition scheme on that external drive:

                    EFI (200MB FAT), BOOT (200MB EXT2) and / (20GB EXT4)

    I choose to add a bootloader to the External drive (not the iMac drive)

    After the successful installation I was shocked when I couldn’t boot my OS X. It's strange because I didn't install any bootloader on maind drive.

    If I removed the external drive, I get a black screen with the grub prompt command!

     

    In panic, I researched online and I decided to give a try to rEFInd. After the installation from the .deb source (it's recommended to install from the .deb file to fix the problem with the Ubuntu 16.x versions) I could boot my OS X.

     

    To restore the original boot menu (and ditch Linux), you can use the startup disk utility on your OS X or you can mount the EFI partition and with the "sudo rm ..." command, remove the “refind” and “Ubuntu” folders on that partition.

     

    Reboot and everything will work like before.