macOS - Making a Bootable macOS USB Flash Drive

By Jack Szwergold • October 6, 2015

Creating a bootable macOS USB flash drive in macOS 10.7 and higher.

If you are using macOS 1.7 (Lion) and higher, you can create bootable USB media using a command like this:

sudo /path/to/Install\ OS\ X\ --volume /Volumes/Untitled --applicationpath /path/to/Install\ OS\ X\ --nointeraction

You need to set the path to the actual “Install OS X [Nickname].app” as well as the volume path to the USB flash drive. Just insert the USB flash drive, open up the Terminal and run that command. It will ask for your administrator password and then output would be something like this:

Erasing Disk: 0%... 10%... 20%... 30%...100%...
Copying installer files to disk...
Copy complete.
Making disk bootable...
Copying boot files...
Copy complete.

The disk erasing process is pretty quick, but the “Copying installer files to disk...” takes forever. Just wait until that finishes and when it’s all done, it’s done and you will have bootable macOS USB flash drive.

How to fix the “This copy of the Install OS X [Something] application can’t be verified. It may have been corrupted or tampered with during downloading.” error.

So you are ready to install macOS from a USB drive or from a download and this error pops up:

This copy of the Install OS X [Something] application can’t be verified. It may have been corrupted or tampered with during downloading.

Frustrating isn’t it. Well, the fix is not to waste time or bandwidth by redownloading a multi-gigabyte installer, but instead syncing the local systems time with Apple’s remote time server when you boot into the USB drive.

Just boot up from that system disk, open up the terminal and type in this command:

ntpdate -u

And it should work fine. If not, open up the Terminal again and set the system time to be some time in the past like this:

date 0901000015

That would set the system time to September 1, 2015 at 00 hours and 00 minutes. Yes, that seems crazy. But it works.

An alternative way of creating a bootable macOS USB flash drive in macOS 10.6 and above.

The main benefit of this alternate method is it works in macOS 10.6 (Snow Leopard) but the general procedure should work in any version of macOS 10.6 and higher.

First open up the InstallESD.dmg hidden in the “Install OS X [Nickname].app” installer like this:

open /path/to/Install\ OS\ X\

Once that is mounted run ls -la on the mounted volume to see its contents:

ls -la /Volumes/OS\ X\ Install\ ESD

Then run asr (Apple Software Restore) to restore the image to your USB flash drive. This command should work in macOS 10.6:

sudo asr restore --source /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg --target /Volumes/Untitled

This variant of the command should work in macOS 10.7:

sudo asr -restore -source /Volumes/OS\ X\ Install\ ESD/BaseSystem.dmg -target /Volumes/Untitled -erase -format HFS+ -noverify

The output would be something like this; when prompted to erase the USB flash drive respond y:

Validating target...done
Validating source...done
Erase contents of /dev/disk3s2 (/Volumes/Untitled)? [ny]: y
Retrieving scan information...done
Validating sizes...done
Restoring  ....10

The “Restoring” process will seemingly take forever but when it is done this will be the output:

Restoring  ....10....20....30....40....50....60....70....80....90....100
Remounting target volume...done

And that new volume would be mounted. But we’re not done yet! The issue is that image will have an alias to Packages but we need a full copy of the actual Packages directory to continue. And this is how we can do that.

First, let’s delete the Packages alias from the USB flash drive:

rm -f /Volumes/OS\ X\ Base\ System/System/Installation/Packages

And now copy the actual Packages directory from OS X Install ESD to OS X Base System/Installation/Packages

cp -rpfv /Volumes/OS\ X\ Install\ ESD/Packages/ /Volumes/OS\ X\ Base\ System/System/Installation/Packages/

Now wait for that to copy to complete. It too will seem to take forever to copy, but when it is done the copy will simply stop. And you would thing we’d be done, but one last thing.

You notice how the USB flash drive is generically named “OS X Base System?” Let’s rename that to match the actual Mac OS installer being used on that USB flash drive like this:

diskutil rename "OS X Base System" "Install OS X Yosemite"

And now let’s “bless” the USB flash drive with the new name as well:

sudo bless --folder "/Volumes/Install OS X Yosemite" -label "Install OS X Yosemite"

Now, the bootable macOS USB flash drive should be renamed ready for use.