How to format/partition a disk from the command line

 diskutil partitionDisk /dev/disk3 GPT jhfs+ foo 10g jhfs+ bar 10g

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Chunk validation failed

When installing Mac OS from the command-R internet recovery boot up, you can use command-L to show the logs. Sometimes you will find that the installation does not happen and you see an error "Chunk validation failed". Apparently this means your SATA cable or hard drive is faulty.  https://apple.stackexchange.com/questions/258522/mountain-lion-reinstall-failure
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The most useful defaults-write options

The following are really useful options to set system-wide for Mac OS X. I'd suggest reading them to guess what they do. You should be able to safely run all of them except the first one which tells spotlight (the search function) to ignore any attached drives forever. If you find that drives take a long time to unmount (eject), then usually it is because spotlight is indexing them (reading them in their entirety) to see what they contain. Hence if you find a disk doesn't want to eject, turn off spotlight for that drive. sudo defaults write /.Spotlight-V100/VolumeConfiguration Exclusions -array "/Volumes" defaults write com.apple.dock springboard-columns -int X defaults write com.apple.dock springboard-columns -int 10 defaults write com.apple.dock springboard-rows -int 7 defaults write com.apple.dock springboard-rows -int 5 defaults write com.apple.dock springboard-rows -int 5 springboard-columns -int 10 defaults write com.apple.dock springboard-rows -int X defaults w
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Erasing firmware password

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On some occasions, like myself, you may be forgetful, and forget what you set your bootup ("firmware") password to. Unfortunately for you, if you boot in recovery mode using Command-R, it still wants you to remember your original password to erase the old one.  The proper way to do this is to take the computer to Apple with proof of purchase and they will do it for you. However, if like me you only buy their much older machines due to their upgradability, you may find that you don't have proof that you bought it in an apple store, e.g. second hand, or you lost the proof years ago. So, how do you reset it? The answer unfortunately, is with great difficulty. This blog page tells you how. Please note that I disclaim responsibility for the below - if you blow up your Macbook it's your fault. Do not follow these instructions. I followed these: https://blog.wzhang.me/2017/10/29/removing-mac-firmware-password-without-going-to-apple.html However, they are not 100% clear on al
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