Jacob Elder <[EMAIL PROTECTED]> [2002-09-28 18:13:11 -0400]: > It appears that du and tar use a different pattern language for their > --exclude-from option. I was trying to predict the size of a backup that > would be performed with tar, and came across a discrepency. > > df reports that I'm using 2882M. > tar --exclude-from says that the backup is 2722M. > du with my tar-friendly exclude from reports that I'm using 2942M. > du without any exclude file reports that I'm using exactly: 2942M.
df is reporting disk blocks free. du is reporting disk blocks used. tar makes tape archives and I did not realize reported a size. However looking at the size of the archive created would be representative of the space used. But tar has its own overhead for storing files and I would expect the size to be larger than the number of bytes consumed by the file. A frequent confusion is that du reports the number of characters consumed by files. In order to get that information you would need either a script to add up the ls -l data or yet a different command. That functionality is not provided by du. The du command asks the filesystem how many disk blocks are consumed by a file. This is usually a larger number of bytes than the file size. A file of one character will consume not just one character but also the entire size of the filesystem fragment size. I am going to wave my hands and say that is a 512 byte block even for the smallest file. Not true anymore but once was always true. Different filesystems implement this differently and that is not the point here. Also, a file could be sparse. Therefore I would expect du to rarely ever give you the same values as if you added up the space occupied by characters. It would rarely be the same size as the tar archive size. The sizes you quoted seem in the right magnitude to just be confusion over file sizes and disk blocks. > The options have the same name, and both commands hail from gnu.org, so > shouldn't they cooperate? I am not convinced by this data that the exclude list is really the issue here. It might be. But the other confusion seems a much more likely explanation. Bob _______________________________________________ Bug-fileutils mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-fileutils
