I have an old Mac I’d like to install Mavericks on but I seem to have lost the admin password. How can I do this?

Believe it or not, you don’t really need to be an admin to upgrade your Mac OS. However, you do need to boot right into the installer rather than try and launch it from your desktop. You might need a machine you DO have admin access to to create the bootable media, but that’s really all you need. Here’s what you need to do:

Before being able to create a bootable OS X installer, you’ll need to do the following first:

• Use the Mac App Store to download the OS X installer app.
• Mount the volume you wish to convert into a bootable installer. This could be removable media such as a USB flash drive or a secondary internal partition.

You can then use the createinstallmedia tool to convert the volume from step two into a bootable installer based off the installer app from step one. To learn how to use createinstallmedia, use the following command in Terminal:

/Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia
For example, assuming you have a volume mounted at /Volumes/MyVolume and the OS X installer app is at /Applications/Install\ OS\ X\ Mavericks.app you could erase /Volumes/MyVolume and convert it into a bootable installer with this command:

sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Mavericks.appYou may need to adjust the path to the OS X installer app in the above command, but once this is done you’ll have everything you need to upgrade your old machine. Just plug the USB drive into your old machine, and restart while keeping the Option key pressed. This will bring up Startup Manager where you can select to boot off your removable media.