I bought three movies on DVD on eBay. I am trying to make .iso backups onto my external hard drive. The first one I tried using Disk Utility, but it only produced a partial copy (without generating any errors) so I switched to using dd
, which worked on the first movie. For both the second and third movie, dd
only partially ran through before giving the following error:
dd: /dev/disk2: Permission denied
1438432+0 records in
1438432+0 records out
736477184 bytes transferred in 212.743197 secs (3461813 bytes/sec)
The number of records/bytes is similar, but not exactly the same, for both movies. I have no clue what else to try, since dd
is as low-level a program I know to use. I have no idea why the error would be generated mid-copy like that. Googling for this kind of error leads to answers regarding improper filesystem permissions (I'm running sudo dd
) and unmounting first (I'm also running sudo umount
), and AFAIK neither would lead to dd
working for the first 700MB and then getting that error.
Also, I have watched these movies all the way through without incident, so the filesystem appears to be good.
Best Answer
While writing this question, I remembered something I did different with the first disk and think I figured it out. For the second two disks I was using
sudo umount /Volumes/DISK_NAME
to unmount the DVD before runningdd
, which generated the permissions error, so I triedsudo umount /dev/diskX
. This works, but only once per boot (it would fail again after one successfuldd
, until I rebooted). But can anyone explain why it worked? I thought the two invocations ofumount
were equivalent.