Permissions for file transfer over target disk mode I have a 2015 iMac that no longer boots. I want to recover the ~1 TB of data on it and transfer to a brand-new iMac. (Through a comedy of errors, my Time Machine drive isn't available.) 

I can connect the two machines via Target Disk mode with a Thunderbolt cable/Thunderbolt 2-to-3 adapter. I tried Migration Assistant, and it recognized the old drive and offered to transfer, but I let it run all weekend and it didn't get off the first step ("Looking for applications and documents to transfer ... "). I tried a few variants, such as only migrating one user account and only migrating Settings (as a test) and all of them hang on the first step.

I can look at the Target Disk on the network and see the user accounts with the appropriate amounts of data on them, but I don't have access to the files because it doesn't have permissions. 

How can I give the Target Disk the appropriate permissions? Can I enter the password somewhere? 

A possible complication is that the old iMac login was via a network user account. I know the various passwords, but I'm not clear on whether the old iMac, now no longer able to access the network, will know them.

My overall question is how to recover the data from the old iMac; if there's a simpler way than connecting via Target Disk mode, entering the appropriate permissions, and copying files to the new machine, that would be welcome too.
I did an almost identical recovery a couple days ago. Heres my answer:

DON'T USE MACOS BUILT IN TRANSFER METHODS

I have found them extremely unreliable, difficult to debug, and unable to resume on failure.

Instead, use rsync!

Connect via Target Disk Mode. Make sure to ignore permissions on the drive.

The following command will recovery everything and preserve metadata including dates, etc.  It works extremely well, is able to resume on failure, and shows progress.

/**
  *
  *  /path/to/source - Path to the disk you want to recovery (or a folder on it if you only want specific things)
  *  /path/to/destination - Path to disk you want the items to be copied to
  *
  */

 rsync -avP /path/to/source /path/to/destination


It will take a while to count files but you will see it counting.

To continue - https://unix.stackexchange.com/questions/67539/how-to-rsync-only-new-files