sharing and permissions on mac HD
I restarted my iMac and lost permission to move all files. I then updated the OS and still have the same problem. When I look at sharing and permissions on macintosh HD, it says "you can only read" and shows "system" as the only name with read and write permission. If I enter my password each time I move a file, it works, but am not allowed to add myself to the sharing and permissions for macintosh HD. How do I correct this?
iMac (27-inch, Late 2013), macOS Sierra 10.12.2