how to check integrity of recovery partition? I recently reinstalled Yosemite from the computer's recovery image.  I'd like to be able to check the integrity of that image (i.e. shasum /Applications/Install*OS*.app/Contents/SharedSupport/{Base,Install}*.dmg
 as seen here.). At the time I could not because shasum and most command line utilities are not installed when you boot from the recovery partition.  I know there is a volume called Recovery HD but I can't access it.  How do I check the integrity of the installer on the recovery partition?

Thank you
You can mount the Recovery volume in your normal booted macOS.

diskutil mount readOnly Recovery


Then you can perform checksums on files as you normally would, on the Recovery volume.

shasum /Volumes/Recovery/*/BaseSystem.dmg


When you're done, you can unmount Recovery.

diskutil unmount Recovery