Make Bootable USB installers for macOS

The macOS installation applications contain a tool that lets you build a bootable USB installer which is handy for bringing an old Mac backk to life. You may need to use an older OS on an older machine, or you may just want to do a clean reinstall that’s faster than downloading over the network.

The installer has a program called createinstallmedia that accepts the name of the removable USB volume. It’s located in the Contents/Resources directory of the installer app.

According to Apple Support, here are the commands for each version of macOS, where MyVolume is the name of your USB drive:

• Sonoma sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• Ventura sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• Monterey sudo /Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• Big Sur sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• Catalina sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• Mojave sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• High Sierra sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
• El Capitan sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

Run the appropriate command in your Terminal and follow the prompts to create your installer.

Fixing Killed: 9

Unfortunately, if you try to run this and you get “Killed: 9” then you need to code sign the createinstallmedia tool.

Switch to the Contents/Resources directory and run the following command:

codesign -s - -f createinstallmedia

It’ll confirm that the signature changed:

createinstallmedia: replacing existing signature

Then try it again.

Fixing Invalid Installer issues

Some older operating systems, like El Capitan, may fail to validate when you try to install them if you are using old installers prior to 2020. These installers have certificates that expired in 2019. The solution is to download newer versions of the installers. But if you’ve already made your installation media and want to save time, disconnect your Wi-Fi connection and change the system date through the Terminal app to the date the installer was created.

Once you are in Recovery mode, go to the Utilities menu in the top navigation bar and open the Terminal app. Type date MMDDHHmmYY replacing the letters as follows:

MM - 2 digit month  01 - 12
DD - 2 digit date   01 - 31
HH - 2 digit hour   01 - 24
mm - 2 digit minute 01 - 59
YY - 2 digit year   > 15

Set the date to the date of the installer or to a date shortly after that installer. Alternatively, download an updated installer with an updated certificate.

If you didn’t disable your internet connection, this date will immediately reset to the current date and time. Disable your internet connection.

Fixing Required Firmware Update issues

If you successfully get the installer to run, the files will copy and the machine will reboot.

If you’re running genuine Apple hardware and you get the message “A required firmware update could not be installed”, the solution is most likely related to the certificate validation for the firmware update too.

If you set your date to a previous year but didn’t disable your Wi-Fi entirely, the date gets reset between reboots.

Restart the machine, hold down the OPTION key and make sure the Wi-Fi connection is disabled. Then start the installer.

Change the date and continue the installation. This time everything will complete.

Sources:

• MacRumours answer for fixing the Killed: 9 error
• Stack Overflow answer for the date fix