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With the arrival of OS X Lion in 2011, Apple changed its software-delivery method to a download model with the Mac App Store instead of using physical DVDs and other media. While downloading an OS X or macOS version offers instant gratification, it means you're left without an installer. This is problematic if you need to reinstall OS X or macOS on a newly formatted hard drive, if you're in an. Sep 06, 2012  How to Restart a Mac from the Mac OS X Command Line To start a reboot immediately from the Mac OS X Terminal, type the following command string at a prompt (either locally or remotely). Sudo shutdown -r now. Next you’ll need to enter the administrator password when requested, that’s because the command is prefixed with sudo, which gives the shutdown command superuser privileges. To boot from a CD or DVD: Restart your Mac while pressing the C key. This is a great way to free your startup volume when you want to test it or optimize it using a commercial utility. To eject a recalcitrant disc that doesn’t show up on the Desktop: Restart Mac OS X and hold down the mouse button, or if you have a late-model Mac, press the Media Eject key as soon as you hear that. May 23, 2016 To boot your Intel-based Mac into any of the macOS built-in startup modes, you must press and hold one or more keys detailed below after turning on the computer. Press the keys immediately after hearing the startup sound, unless otherwise specified. Jun 28, 2020  UNetbootin downloads the Ubuntu ISO, converts it to an image format the Mac can use, creates the boot chain needed by the installer for the Mac OS, and then copies it to the USB flash drive. Download the macOS version of UNetbootin from the UNetbootin GitHub website.

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Here are some technical details to understand what this hint is talking about.
First, a bootloader was not restored. Mac OS X has no boot loader in the traditional sense. What you are referring to is the boot code in the Master Boot Record of disk.
The first sector of the GUID Partition Table (GPT) disk contains is a Master Boot Record (MBR). Traditionally, the MBR contained a bootloader that would start the system running. Mac OS X does not normally use this bootloader.
Mac OS X normally uses EFI. The EFI bootloader location is stored in various NVRAM variables that indicate what file to load in order to boot the computer. EFI is much more advanced than older boot systems in that it includes the ability to mount and read file systems.
However, the Macintosh also supports Boot Camp. In order to support Boot Camp the Macintosh will boot from the MBR as described above. The boot settings in NVRAM can be set so that the Macintosh will boot using the MBR instead of the normal EFI settings. This is what makes Boot Camp work. (This is an Mac extension that is not a part of EFI.)
The Ubuntu installer changed the bootloader in the MBR and also set the system NVRAM variable to boot from the MBR. This made it so that your main disk would not show up.
Resizing the partition causes Disk Utility to erase the MBR bootloader and return the system to using EFI.
I would have to guess that opening the Startup Disk Preference Pane would have allowed you to switch back to OS X, although the Ubuntu loader still would have been present. You would see that in the Startup Disk Preference Pane as a selection to boot into Windows. :-)
Just some fun technical knowledge to explain what is really happening.

Yep, also rEFIt is not a bootloader, but rather an EFI executable that allows more control over the default Mac EFI functions (and some other useful EFI tools).

Good explanation. This also goes to show why you in general need to be very careful with anything non-Apple that modifies partitions or boot loaders. The way Apple deals with the MBR is actually rather non-standard. Typically, the MBR is not used at all with EFI, a small amount of data being written there only to let non-EFI systems know that the drive is not blank. Apple actually does write a proper Master Boot Record for the purposes of allowing systems that do not support EFI (Windows XP, and all 32-bit versions of Windows Vista/7) to boot natively. So you have a system with both a Master Boot Record, as well as EFI boot info written to NVRAM. Windows and Linux based disk utilities don't expect this setup and results may be different than you would expect.

Thanks for the interesting information. I did indeed try to reset the startup disk from System Preferences, but it didn't work. Perhaps it was because I had booted from an external drive.

So is there someway to manually erase the MBR bootloader and/or return the system to using EFI through a command console of some sort before entering the OS or through the terminal using the OS X boot disc? I am having the same problem as the OP, but I cannot see the primary partition in the disk utility using the boot disc, and I can't use the trick the OP used.

Hello, being very new to this thread, I want to point out the big trouble I have . After installing BOOTCAMP on the 5 gb partition and running everything as described, I cannot boot the Mac or the WIndows . I presume it starting straight in Windows with a black screen and the message with DISK ERROR , PRESS ANY KEY TO RESTART comes up, the chime is there also. If pressing any key nothing happens . Tried a number of times to restart while holding OPTION KEY. Only them I got a light grey screen with a padlock and a box where I supposed to introduce a password . Tried that to insert my usual Mac admin password, is not working . I have inserted as well the original disk OS 10.5 to run the disk utility, it doesn't respond to C or any other command . I have tried T target mode, it doesn't take a target mode or maybe I am doing something wrong . Please help . Thanks guys .

I'm having the exact problem as you describe it, but when I go to disk utility, and select the volume, it only shows one disk partition, the one that I tried to boot windows on, and not my original partition, and I can't wiggle the little arrow thing like you described. The partition that shows up is only a fraction of my hard disk memory, but if, instead of 'current', I select multiple partitions, then my full memory shows up. How do I reboot back into Mac OS X??

I just was tinkering with Ubuntu 9.10, trying to install on a USB hard drive. It was successful, but could no longer boot OS X. I found this, but I couldn't change partitions in DiskUtil. Then I remembered that OS X is based off Unix/BSD. Looked up the manuals for fdisk. Used it from command terminal from OS X install DVD.
fdisk -u /dev/disk0
fdisk here is very similar to the DOS fdisk program, just designed for UNIX
the -u tells it to update MBR without modifying partitions
/dev/disk0 is the hard drive. yours may differ, but i doubt it
This fixed my problem.
Long story short, yes you can do it easily from command line, just boot your install DVD. In terminal, type the command listed above.

Hi Chris.
Same problem for me, same fix that worked perfectly well. I knew my data were not corrupted but only hidden but I was afraid to get the situation worse by doing some hazardous tries.
I was just about to install Refit (maybe it would have solved the problem as well..) when I found your post.
Thank you all people who take time to write down their experience for others.
Now, I am wondering how to get Ubuntu work on my external drive and MacBook..
Thanks again.
Benoit, France.

Thank you very much! This hint saved from reinstalling my MacBook.
I damaged my Bootloader while preparing a Hackint0sh-USB-Stick - this is still working with OS X 10.6.4

Thanks! I did the exact same thing and this hint saved my bacon. Kudos..

Hello,
Thanks a million !
This is the only post I found with information that did work and made me able to boot normally, instead of having the 'Waiting for root device' message, and seeing the 'EFI Boot' drive when pressing Option key on boot.

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None of the above worked.
My HDD is encrypted, would that be an issue?
I tried..
fdisk -u /dev/disk0
..no results.
I also tried..
fdisk -e /dev/disk0
flag 2 (for extended drive)
write
quit
reboot
..no results
Please help, I have a lot of sensitive data, for the most part is back up, but the most recent data isn't and is extremely sensitive.

Here we have penned down easy to follow guide for you, it is about to create and boot from a Linux USB drive on Mac.

So, let us have a look at the details of this process. If you have just bought a MacBook Air, then make sure that you do a dual boot, Mac OS X, completely and thoroughly with Ubuntu Linux.

Furthermore, if you are using Windows, then this bootable process comes out to be fairly easy and simple. It does not any involve many technicalities.

Moreover, if your MacBook Air does not have a CD drive, then you can go on creating a live USB right there in Mac OS X. Now, coming to the main topic of this piece of writing, below you read the desired and needed details:

Method to Create and Boot from a Linux USB Drive on Mac

This is a tricky and a little bit of complicated procedure if you want to carry out a booting process from a Linux USB drives!

But if you are going to follow the below-mentioned steps, then we are sure that your job will become an ease. We have divided this guide into a certain and specific number of steps.

Still, if you have any question on this booting process, then you can ask from us! This whole guide and method are based on seven steps.

And it is not expected from you to skip any of the steps. Keenly follow this guide and boost from a Linux Usb drive on any Mac system model of yours.

Step 1: Formatting the USB Drive

The very first step is that you have to carry out and do the formatting of your USB drive. In this Mac OS X, there you are going to see specific kind of file system that needs formatting from your side.

Apple demand from its users to follow these standards and rules and you need to follow them too. This file system is called and marked with the name of Mac OS Extended or it is identified with the name of HFS Plus.

Hence, in this step, the concerned user has to be format his USB drive in the form and version of Mac OS Extended format.

Simply plug in the USB key and there you need to access the Disk Utility program. Choose the USB drive that you want to be formatted.

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After that, hit on the tab that states the Partition tab and selects 1 Partition. Now, you can change and revise the Format right to Mac OS Extended.

Most importantly, you have to make sure that the partition scheme is available in the form of a GUID Partition Table. Finally, click on the Apply button and get started on formatting the USB drive of yours.

Step 2: Downloading Ubuntu Linux

Moving to the second step of this guide, now you have to do the downloading of ISO image of Linux desktop.

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What you can do is to visit and reach to the Linux website. There you can download any of your favourite and desirable Ubuntu desktop OS. Besides, if you are making use of Macbook Air, then it is important for you to get the 64 Bit version.

Step 3: Converting ISO Format to IMG Format

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Mac os x yosemite download. You have to keep in mind this critical point that the file you have downloaded, it is present in ISO format. Now, you need to convert and transform this file all into IMG format.

For this conversion job, you can make use of hdiutil command tool. Once the file is going to be successfully converted, then then your file will show extension in the form of IMG.

Step 4: Getting the Device Number for the USB Drive Of Yours

In the fourth step, the user has to get hold of the device number of USB. For this step, you have to run a specific and particular command.

Once you enter the command, then a list will be provided to you in which you will get all of the disks information that is installed in your system.

You can identify and know about the USB disk of yours on the basis of its size. Still, if you think that there are chances and probability of confusion, then it will better if you plug and insert just one USB drive. As soon as you get the disk number, then the next proceeding is going to be started.

Step 5: Creating the Bootable Version of USB Drive

Now you have entered into the process of creating and developing a bootable version of the USB drive. You can use add command in this regard.

This is one of the powerful commands that you can use and try out. Furthermore, you need to use it with much care and caution.

If you fail to remember the USB drive number of yours, then there is a chance that you may corrupt and infect your Mac OS X system. This step will take a few of the minutes of yours to proceed and move onto the next step.

Step 6: Complete the Process Linked to a Bootable USB Drive

When you see that this specific command known as dd command is done with its processing, then you will get a dialogue text box.

This box will communicate a message to you that the disk that you inserted, it failed to get readable from your PC computer system.

Upon getting this message, there is no need to click on the options that states Initialize, Ignore or on the button of Eject just now.

Simply access the terminal and use the respective command for the sake of ejecting your USB disk. Once it is going to be ejected, then you can click on the Ignore button present in the dialogue box.

On this step, your bootable USB disk is all set and ready.

Step 7: Check And Verify Your Newly Created and Developed Bootable USB Disk

Startup Keys Mac Os X

Moving to the last step of this process! It is about checking as well as verifying your newly created and upgraded bootable USB disk.

You can test this phase as well. For that, you have to plug in the bootable USB and after that, you have to allow your system to go through the booting process.

Moreover, when Apple tune starts and initiates up, then you need to keep on pressing and holding the option of Alt key.

This is all about this guide, this is how you can create and boot from a Linux USB drive on Mac system of yours.

Once you follow all these steps of this guide, this whole lengthy processing and job will become easy for you.

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This testing and verification phase is very important for you. It will remove all queries and you can well know whether you have proceeded this step correctly or not.

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Conclusion!!!

We hope that this guide will make your job a little bit easy and convenient for you. If you still have any queries on creating a bootable USB disk from Linux USB drive for Mac, then you can ask from us any time.

To catch up with the guides like dual booting, we will sooner share details about it. Keep connected with us.

If you had previously followed this kind of method and it did not work out for you, then we guarantee you that it will work for you now.