You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful if you want to install macOS on multiple computers without downloading the installer each time, or you're unable to install a compatible macOS from the Finder or macOS Recovery.
Creating a bootable USB drive and using it to reinstall macOS is a bit of a lengthier process compared to simply updating macOS from the Software Update section of the System Preferences, but it has its benefits.
But creating a bootable USB disk allows you to install or update macOS on multiple systems without having to download the installer on each Mac. This can save quite a bit of time, considering the most recent versions of macOS have an installer size of 12GB.
Those drives often have their firmware hacked to report a false size to your operating system. Not only will the transfer speeds be painfully slow, but using them may also result in loss of data or even a damaged USB port.
Apple has changed the method for downloading versions of the operating system of macOS. While the installers were previously available to download via the App Store, newer versions (macOS Mojave and later) update the system from System Preferences.
To download the latest version of the macOS installer for installing on a USB, open up the System Preferences and navigate to Software Update. You should see the option to download the installer here.
In the event that you are already running the latest version of macOS, you might not see the option to download the installer in System Preferences. In that case, use the App Store method detailed above. This will force System Preferences to download the installer, which you can then use to create the bootable disk.
Terminal offers the easiest way to create your bootable USB drive to install macOS. Just replace the MyVolume portion of the commands below with the name you gave your drive in the Disk Utility step above.
Take note that the commands differ slightly for creating bootable USBs for different versions of macOS. If you are going to create a bootable drive for macOS Monterey, use the command below as it is. Otherwise, replace Monterey with the macOS version name (for example Mojave).
Copy and paste the command you need above into your Terminal window and press the Return key. After entering your password, confirm you want to erase the USB drive by typing Y followed by Return. Terminal will now erase and create your bootable USB drive, ready for you to boot from.
You should now see an option to select your USB drive as a startup disk. After selecting it, your system will boot off your USB drive and enter macOS Recovery with the macOS Monterey installer appearing on your screen. If you want to erase your disk first, to do a clean install, quit the installer and run Disk Utility from the Recovery menu. You can format the drive and then go back to the Recovery menu and install macOS Monterey.
In some cases, Intel Macs with a T2 chip (Intel Macs released after 2018) may not allow you to boot a macOS installer from an external drive. This is due to a setting in the Security Startup Utility that needs to be adjusted. This can be done by following the steps explained below:
You can create a fresh installation of macOS, restore from a Time Machine backup, or access tools like Disk Utility from the macOS Recovery screen. You can also use your USB drive to upgrade macOS to the latest version. If you need to troubleshoot your Mac without a network connection, this USB drive could be a lifesaver.
It goes without saying that you will need an internet connection to download the software and you may need it while installing the version of macOS if it needs to check for firmware or confirm your iCloud credentials.
You can also run the Mac operating system directly from an external drive rather than your built-in startup disk, this is handy if you are testing new versions of the Mac OS. The process is different to the one described above though, and we cover it here: Read about How to run macOS on an external hard drive here.
Select drive, replaced by the name of your USB device if one is already attached, lets you select your target device. You will be warned if the storage space is too small for your selected ISO.
Flash! will activate when both the image and the drive have been selected. As with Disk Utility, Etcher needs low-level access to your storage hardware and will ask for your password after selection.
A cloned version of your macOS installation on a portable USB drive can be invaluable if your system suddenly fails to boot. It can give you troubleshooting options and even permit you to keep working with an identical copy of your files. While internal hard drives are the best way to create bootable copies of your system, a USB drive can also work. You will learn in this guide how to install macOS on a USB drive.
Making a bootable macOS Big Sur USB drive is a quick and clean way to install a fresh copy of macOS on your Mac. This hands-on tutorial is valid for both the public and developer beta versions of macOS Big Sur, and will also work with the final version of Big Sur upon its release later this year. Simply follow our step-by-step guide for the full details.
Creating the USB installer drive is easy, but actually using it can be challenging for users running Macs with Apple T2 Security chips. The aforementioned steps walk you through the basic process of creating the installer, but the video walkthrough goes even more in depth.
To boot from the MacOS Catalina boot disk, connect it to a Mac, then reboot the computer and hold down the OPTION key to boot into the boot menu, where you will be able to choose the MacOS Catalina installer drive as a boot option.
The MacOS Catalina boot disk will allow you to install MacOS Catalina as an upgrade, and also to perform clean installations of macOS Catalina if desired. You can also access the regular bootable installer utilities, including Disk Utility for formatting and partitioning drives, and Time Machine recovery tools for restoring from backups.
This is the 3rd time I make a bootable drive. Withvery one of the 3 usb thumb drives that I used I got the same error message telling me that Catalina could not be installed because the copy of the install application is damaged. I downloaded Catalina from the Apple store! I also tried to install from the network but the install never ends, it goes into some sort of loop where the Apple logo keeps appearing and disappearing. The thing was running all night and never finished. When I plugged the Macbook air in Target mode to my MBP I saw that I had three drives! I erased all, started all over but going nowhere. Several times. Nothing works. I cannot even re-install the original system (Mavericks)
I downloaded the Catalina app to the applications folder on a second Mac running Big Sur. (Side note, the download tried to install too, which scared the hell out of me, but the install seemed to abort before going far enough to do any damage,
I then ran the sudo command as directed, and everything SEEMED to work until the last step. It erased the disk (thumb drive), copied the file to the drive, and gave some sort of message about completion sucess, but the thumb drive kept flashing like something was going on. I left it like that for 45 minutes and it kept flashing. So I went back to finder and tried to eject. And it would not let me eject. I had to do a force eject. Seemed like a bad sign.
Putting aside the USB installer drive for a moment, you might try booting the Mac directly into Recovery Mode, or Internet Recovery Mode, by rebooting and holding down Command+R to enter into Recovery Mode. Once in Recovery Mode, use Disk Utility to repair the startup disk, and, if there is no working operating system, trying to reinstall MacOS from there. It will attempt to install whatever version of Mac OS came on the computer. (Make sure you have a backup of the important data just to be sure, before updating/installing any system software)
There are many nice apps that offer a quick Mac cleanup. Among those, CleanMyMac 3 is our favorite as it looks most user-friendly of all. It scans your hard drive for old caches, broken apps, and app leftovers so you can remove all unwanted files in a minute or two. After all, a newly installed OS X feels better on a clean computer.
If this is the case, please change the 4M to be 4m. Additionally, increasing the blocksize (bs) will speed up the write progress, but will also increase the chances of creating a bad USB drive. Using the given value on macOS/OS X has produced reliable images consistently.
To boot from an alternate drive on an macOS/OS X system, bring up the boot menu by pressing the Option key immediately after powering on the device and select the drive you want to use.
One of the problems with the release of a major operating system update like macOS Catalina is the amount of times it has to be downloaded. As Apple usually intends each Mac or MacBook needing to be updated to download it, the process isn't really efficient enough for instances where many Mac desktops need the upgrade, like in a school or business if there isn't device management or macOS Content Caching for whatever the reason.
While in the olden days it was possible to get the software update on physical media, Apple doesn't offer that option anymore. However, it is still possible to create your own media, such as a spare USB thumb drive, that can do the same job.
After the download has finished, macOS will automatically start the installer. Press Command-Q to quit the installer before it continues, as the update will be deleted upon installation.
You need an external drive to turn into a bootable version, and since it needs to be portable, your best choice is a USB thumb drive with a capacity of 16GB or more. Be aware that the drive will be wiped as part of the process, so ensure there isn't any precious data on the drive that c