Startosinstall return code 5

I just created my first workflow on a USB flash drive. The process begins but then stops with “startosinstall return code 5”. The log says that it is having trouble converting the disk to APFS, yet the hard drive of the target machine is already APFS with Big Sur. Any ideas?

Is it possible that the APFS file system was created with a newer version of macOS and that you are downgrading? That may explain the error. If so, just format the drive in disk utility and then you should be able to run the workflow.


Hello Tim, thanks for the suggestion. We are not downgrading, rather trying to install the latest version of Big Sur. But just in case, I formatted the drive a few times from Disk Utility and came up with the same error.

The log file is attached here. Do you see anything else that could be the issue?

Link to Log File

Please look in the log:

cat /var/log/install.log

You can send it to if you don’t want to post it here.