On 24 Feb 2008, at 11:46, Etaoin Shrdlu wrote:
On Sunday 24 February 2008, Stroller wrote:
I've done this loads in the past, and never been aware of any file
corruption, but I guess I'm just paranoid today. Perhaps I shouldn't
use the -v flags during my copy - it's reassuring to see the files
being copied, but what if I overlooked a bunch of errors in the
middle of all those thousands of "copied successfully" confirmations?
What if something has gone wrong during one of the two copies?
Well, in that case cp will have a nnonzero exit status. Look:
...
$ cp a b destdir
cp: cannot open `b' for reading: Permission denied
$ echo $?
1
...
I think this should hold for the majority of cases/errors cp might
encounter during the copy.
Good point. I should have checked this when I first made the copy
using cp, and will do so in the future.
Of course, this does not detect a succesful, but somehow corrupted,
copy
(which should be exceptionally rare, anyway).
Well perhaps I'm just being paranoid today.
But how do I know that a successful, but somehow corrupted, copy has
not occurred?
What makes you confident that these are rare? I don't ask this to be
antagonistic, just to increase my own confidence in the `cp` command.
Is there any way to check the integrity of copied directories, to be
sure that none of the files or sub-directories in them have become
damaged during transfer? I'm thinking of something like md5sum for
directories.
I'm not aware of any such tool (which might exist nonetheless, of
course). However, on the filesystem, the objects that we
call "directories" are just index files holding filenames and pointers
to inodes. Running a checksum on the directories themselves would not
guarantee against corruption of any of the contained files, since file
data is not contained in the directory.
Naturally.
Perhaps I should have phrased my question differently: "Is there any
way to recursively check the integrity of copied directories of
files?" However the words "to be sure that none of the files or sub-
directories in them have become damaged during transfer"
Thus, to be accurate, such a
tool would have to scan the directory, find each file, and perform a
checksum on it, which would result in something not much different
from
the find command you suggested, in terms of resource usage.
I have to admit that I haven't run this command and I don't have any
idea what its actual resource usage would be. I guess I'd be happy
with a lower-grade of checksumming, if it would reduce the runtime to
acceptable levels. With md5sum one can be - barring certain malicious
external attacks - quite certain that a copied file is identical to
the original. I would be happy with a "the file's there and it looks
ok" level of confidence.
Stroller.
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