>> a PC. Another technique I have used when I didn't have immediate access
>> to a wiping program (and *think* it is okay although not as good as
>> doing a wipedisk) is to overwrite the offending file with another
>> larger one, i.e. "copy [bigfile.ext] [offending file.ext]" and of
>> course, then deleting the
>
>This may not work. On RT11 (I think) it certainly won't work.
Right...
>What some OS's do is create the new file in a suitable (contiguous) free
>area on the disk and then mark the existing file as unused space. RT11
>does this because all files have to be contiguous on that OS.
Good explanation...
>Of course then the original (deleted) data is still on the disk.
Yep...
>Deleting files and then compressing an RT11 disk should be OK unless the
>files are at the end of the disk. Compressing and then creating a large
>file (large enough to overwrite the rest of the disk) should be safe.
Unfortunately not... the only way to guarantee it is if there are LOTS
of files on the disk, and the file deleted existed at a point in the
directory less than the total size of all the following files. Too much
to have to check before you are sure it is gone...
Teh creation of the large file simple creates a directory entry... the
actual disk surface defined by the new entry is not touched, so the
data could still be there, hidden inside the larger file. Now if you
did something to that file to overwrite it's contents, then it would
be gone.
It's been a while since I had to do this, and I had a program to do it
for me anyway... but on a stock RT-11, you might be able to mount the
file as a logical device, then FORMAT or INIT it, or do a COPY/DEV
to it...
Megan Gentry
Former RT-11 Developer
+--------------------------------+-------------------------------------+
| Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry!zk3.dec.com |
| Unix Support Engineering Group | (home): mbg!world.std.com |
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Received on Thu May 27 1999 - 22:56:37 BST