C7 Possible Bug But I Can’t Determine What Tool Has The Problem
Hi all,
I’m writing a script that uses rsync to sync 2 dirs on C7. I noticed a strange behaviour.
I have 2 dir: src and dest. In src dir I generate a testfile with “dd if=/dev/zero of=testfile bs=1M count=100” and when I run “du -h testfile” I get the correct result. Then I sync src/ to dest/ using “rsync -avS
6 thoughts on - C7 Possible Bug But I Can’t Determine What Tool Has The Problem
https://wiki.archlinux.org/index.php/Sparse_file#Creating_sparse_files
In short, rsync is being told to create sparse files with the -S flag, so it does. Could you share what you did with the urandom then zero test you mentioned? I’m curious what exact sequence of commands you used.
Il 15/01/20 17:51, Jon Pruente ha scritto:
Hi Jon, I wrote in the first mail the script with the current order of command that I used. Try to run in a bash script and you will see the result.
If not my sequence is:
dd if=/dev/zero of=src/testfile bs=1M count0
rsync -avS src/ dest/
du -h dest/testfile du -b dest/testfile
for urandom:
dd if=/dev/urandom of=src/testfile bs=1M count0
rsync -avS src/ dest/
du -h dest/testfile du -b dest/testfile
without –sparse the same as first sequence without -S option.
But why du reports 0M when with -b reports correct bytes and why this happens only with zeroed file?
I don’t know if in the original post mail script
Ah, I misunderstood what you meant. I had thought you might have created a file with urandom first and then overwrote it with zeros. This is behaving as expected with sparse files. You can create a sparse file with dd by using seek:
https://www.thegeekdiary.com/how-to-create-sparse-files-in-linux-using-dd-command/
Il 15/01/20 18:54, Jon Pruente ha scritto:
Thank you for the suggestion. I meant -S of rsync to use disk space efficiently but this is a (great) misunderstood. Now I read again rsync man page (and your link) and this means “treat sparse files efficiently to save space on disk”. My question is: is rsync capable to detect sparse files from “regular”
files? If -S is invoked and no sparse files are not in dataset, it treats those files as sparse files or “regular” files?
Why I get different behaviour using urandom and /dev/zero? This is casual/accidental?
Thank you again for your help.
That’s not a bug, that’s what sparse files are.
In POSIX systems, it’s possible to treat a regular file like memory, and one of the things you might do with such a feature is use a file to keep track of the last time a user logged in.
Il 16/01/20 02:21, Gordon Messmer ha scritto:
Thank you for your answer. I appreciated it.