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There are many posts on the Internet where instructions are given for creating OS X USB installers by using the TransMac and other such applications on a Windows machine. Many of these posts assume one is starting with a disk image (.dmg) file made from an existing OS X USB flash drive installer.

An InstallMacOSX.dmg file for OS X El Capitan, can be downloaded from the Apple website How to download macOS. While this file can be restored to a flash drive, the result is not a working OS X El Capitan USB installer. The same is true for the macOS Sierra file InstallOS.dmg file, which can be downloaded from the same Apple website.

How can I use Windows to create an OS X El Capitan or macOS Sierra USB flash drive installer from a .dmg file, which can be downloaded from Apple?

2 Answers 2

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Note: Links to instructions for other versions of OS X/macOS can found here.

User Josué Mpindi posted a question, where this answer was confirmed to work for macOS Sierra in a comment. Note that where necessary, you would need to substitute Sierra references for El Capitan in the instructions.

Note: A version of this answer, which uses macOS to create the USB flash drive OS X El Capitan installer, can be found here.

Using Windows to create an USB flash drive OS X El Capitan installer requires third party software beyond just TransMac. The steps below outline one possible method for creating an USB flash drive OS X El Capitan installer using Windows and other free third party tools.

Note: These instructions will not work for Yosemite. For the correct Yosemite instructions, see this answer.

  1. Use Microsoft Edge (or some other web browser) to download the following installers to your Downloads folder. The file names are current as of September 22, 2022. If both 32 bit and 64 bit versions are available, the 64 bit version is given in the table.

    Product Use Installer Type
    El Capitan 10.11 Free for use on Mac computers InstallMacOSX.dmg Mac Disk Image
    7-Zip Free 7z2201-x64.exe Application
    TransMac 15 day free trial tmsetup.zip Compressed (zipped) Folder
    Paragon Partition Manager Community Edition 64bit Free for personal and home use Paragon-1081-FRU_WinInstallDemo_x64_17.9.1_000.exe Application

    If you get the message “InstallMacOSX.dmg can't be download securely”, then select “Keep”, as shown below.

  2. Install all downloads except “El Capitan 10.11”. If you wish, the installed downloads can be uninstalled from the Windows Control Panel after use.

  3. Use a 7-Zip File Manager application window to extract the OS X Install ESD folder and the InstallAssistant.icns file to your Downloads folder. From a File Explorer window, start by navigating to your Downloads folder. In this window, right click on the InstallMacOSX.dmg Mac disk image file, then select "7-Zip" > "Open archive". This should open a 7-Zip File Manager application window. In this window, right click on each file or folder in the order given in the table below, then select the corresponding action. When finished, close the 7-Zip File Manager application window.

    File or Folder Action Type Comment
    Install OS X Open Folder
    InstallMacOSX.pkg Open Inside * Package File
    InstallMacOSX.pkg Open Folder
    InstallESD.dmg Open Mac Disk Image File
    OS X Install ESD Copy To… Folder See footnote ‡
    OS X Install ESD Open Folder
    BaseSystem.dmg Open Mac Disk Image File
    OS X Base System Open Folder
    Install OS X El Capitan.app Open Folder
    Contents Open Folder
    Resources Open Folder
    InstallAssistant.icns Copy To… Apple Icon Image File See footnote ‡

    The destination should be your Downloads folder. If this Downloads folder exists on a volume that is not NTFS formatted, then see this answer.

  4. Insert a 16 GB or larger flash drive into an USB port. If prompted, you do not need to initialize the flash drive.

  5. Open the TransMac application with Administrator privileges. (In other words, right click on the TransMac icon, then choose "Run as administrator" or "More" > "Run as administrator".) In the TranMac application window, take the following actions.

    • Select "Tools" > "Settings" from the pulldown menu. In the "General" tab of the "Settings" popup, select the same copy options as shown below.

      TransMac General Settings

      Select OK when finished.

    • Right click on the USB flash drive icon in the treeview pane, then select "Restore with Disk Image". In the "Restore Disk Image to Drive" popup , choose to "Open" the OS X Install ESD\BaseSystem.dmg Mac disk image file in your Downloads folder as the Disk Image to restore, then select the OK button. Next, select Yes in the "Last Warning!" popup.

  6. Open the Paragon Partition Manager 17 CE application. Select to resize the partition with the Apple HFS volume on the USB flash drive to maximum size, as shown below. Next, select the "Change now" button. When finished, select the "Close" button.

    Next, select to change the volume label on this Apple HFS volume from "OS X Base System" to "Install El Capitan", as shown below. Next, select the "Change now" button. When finished, select the "Close" button.

    When finished, close the Paragon Partition Manager 17 CE application window.

  7. In the existing TranMac window, take the following actions.

    • Select "Tools" > "Refresh Drive List" from the pulldown menu.

    • Navigate to root folder on the USB flash drive volume labeled Install El Capitan, as shown below.

      Root

    • In the listview pane, right click, then select "Copy Here", as shown below.

      Root Copy Here

      Select to copy the OS X Install ESD\BaseSystem.chunklist and OS X Install ESD\BaseSystem.dmg files in your Downloads folder. Repeat to copy the InstallAssistant.icns file in your Downloads folder.

    • In the listview pane, right click on the InstallAssistant.icns file, then select "Rename". Change the name to .VolumeIcon.icns. When finished, the treeview and listview panes should appear as shown below.

    • Navigate to System\Installation folder on the USB flash drive labeled Install El Capitan, as shown below.

      System\Installation folder

    • In the listview pane, right click on the Packages file, then select "Delete". When prompted, select the Yes button in the popup to confirm.

    • In the listview pane, right click, then select "Copy Here", as shown below.

      System\Installation Copy Here

      Select to copy the OS X Install ESD\Packages folder in your Downloads folder. (This may take a while to complete.) When finished, the treeview and listview panes should appear as shown below.

    • Close the TransMac window.

  8. Use the File Explorer to delete the OS X Install ESD folder and InstallAssistant.icns file in your Downloads folder. If you wish, you can also delete the downloaded files. When finished, close the File Explorer window, then empty the Recycle Bin.

References

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  • 2
    Nice one! I added this to the canonical list. Hope you don't mind. apple.meta.stackexchange.com/q/2418/85275
    – Tetsujin
    Commented Sep 25, 2022 at 8:56
  • I'm following this guide to the letter, but when I get to step 6, Paragon Partition Manager doesn't recognize that the USB has a partition on it; it just shows it as "Not formatted." See this screenshot (with my main drive hidden with a black bar): i.imgur.com/hIPI76l.png. I tried running through the previous steps again, but no dice. For what it's worth, I'm trying to create a Yosemite installer rather than El Capitan, but the folder structure in the dmg file is the same as this guide so I don't think that would be a problem. Commented Oct 10, 2022 at 7:05
  • @user2752467: The steps for Yosemite are different than for El Capitan. This is because Yosemite uses the Apple Partition Map (APM), which is not recognized by the Paragon Partition Manager. El Capitan uses the GUID Partition Map instead, which is recognized by the Paragon Partition Manager. I added a new question and answer to cover Yosemite. Commented Oct 10, 2022 at 19:28
  • Just one addition: Do not unpack the InstallMacOSX.dmg file to an exFAT formatted partition! I got an error that one file could not be copied! By using an NTFS formatted partition all the files in InstallMacOSX.dmg could be unpacked and copied there.
    – Fred -
    Commented Oct 25, 2022 at 18:17
  • @Fred-: I posted a new answer which address your concerns. Basically, the file that could not be copied is actually an alternate data stream. You can ignore this error and proceed with the instructions to create the USB flash drive OS X El Capitan installer. In other words, you do not need an NTFS formatted partition. I also update my first answer so other users will be informed. Commented Oct 27, 2022 at 13:04
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The instructions for using Windows to create an USB flash drive OS X El Capitan installer are given in my first answer. This answer addresses concerns posted by user Fred - with respect to my first answer.

My first answer used the "Copy To…" action to extract the OS X Install ESD folder to the users Downloads folder. Here, this Downloads folder is assumed to be in a NTFS formatted volume. However in a now deleted post†, Fred - stated the following.

And yes, my Downloads folder is NOT on the system drive and NOT NTFS but ExFAT. One reason for changing the Downloads directory is that my system drive is way too small for all the smaller or bigger downloads. I am convinced, quite a lot of people use non‑default system setups, for instance do not install programs on the system drive but on another partition (as I do whenever possible). ExFAT comes in handy for various reasons, of course not for program installations and things that require NTFS permissions, but for downloads and shared drives this is very good.

BTW, I believe the "system drive", that Fred - referred to, is actually called the "Windows partition" in Microsoft documentation.

In this answer, I used the "Copy To…" action to extract the OS X Install ESD folder to a dma\downloads folder I created on an exFAT formatted drive E:. I received the following popup with a single error message.

This message is repeated below.

Cannot open output file : The filename, directory name, or volume label syntax is incorrect. : E:\dma\Downloads\OS X Installer ESD\BaseSystem.dmg:com.apple.diskimages.recentcksum

By examining the string BaseSystem.dmg:com.apple.diskimages.recentcksum, one can determine this string is referring to an alternate data stream. Since exFAT does not support alternate data streams, an error message was generated. After further testing, I can state the following.

This answer and my original answer do not require any alternate data streams which can or can not be copied from the InstallMacOSX.dmg file downloaded from Apple.

So, if this is the only error message in the popup, then you can ignore the message and proceed with creating the USB flash drive OS X El Capitan installer.


†Actually, Fred - originally posted an answer which was edited by Fred -, then me and finally a moderator. At the time of this posting, the moderator converted the answer to a comment, then deleted the answer.

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  • @Fred-: I think you still can not post comments. If this is true and you wish to communicate with me, then try editing your deleted answer. I believe I will get a notification of any changes. Commented Oct 27, 2022 at 12:51

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