tar: file changed as we read it

Question

I am using make and tar to backup. When executing makefile, tar command shows file changed as we read it. In this case,

Answer 1

Simply using an outer directory for the output, solved the problem for me.

sudo tar czf ./../31OCT18.tar.gz ./

Answer 2

Although its very late but I recently had the same issue.

Issue is because dir . is changing as xyz.tar.gz is created after running the command. There are two solutions:

Solution 1: tar will not mind if the archive is created in any directory inside .. There can be reasons why can't create the archive outside the work space. Worked around it by creating a temporary directory for putting the archive as:

mkdir artefacts
tar -zcvf artefacts/archive.tar.gz --exclude=./artefacts .
echo $?
0

Solution 2: This one I like. create the archive file before running tar:

touch archive.tar.gz
tar --exclude=archive.tar.gz -zcvf archive.tar.gz .
echo $?
0

Answer 3

I also encounter the tar messages "changed as we read it". For me these message occurred when I was making tar file of Linux file system in bitbake build environment. This error was sporadic.

For me this was not due to creating tar file from the same directory. I am assuming there is actually some file overwritten or changed during tar file creation.

The message is a warning and it still creates the tar file. We can still suppress these warning message by setting option

--warning=no-file-changed

(http://www.gnu.org/software/tar/manual/html_section/warnings.html )

Still the exit code return by the tar is "1" in warning message case: http://www.gnu.org/software/tar/manual/html_section/Synopsis.html

So if we are calling the tar file from some function in scripts, we can handle the exit code something like this:

set +e 
tar -czf sample.tar.gz dir1 dir2
exitcode=$?

if [ "$exitcode" != "1" ] && [ "$exitcode" != "0" ]; then
    exit $exitcode
fi
set -e

Answer 4

To enhance Fabian's one-liner; let us say that we want to ignore only exit status 1 but to preserve the exit status if it is anything else:

tar -czf sample.tar.gz dir1 dir2 || ( export ret=$?; [[ $ret -eq 1 ]] || exit "$ret" )

This does everything sandeep's script does, on one line.

Answer 5

If you want help debugging a problem like this you need to provide the make rule or at least the tar command you invoked. How can we see what's wrong with the command if there's no command to see?

However, 99% of the time an error like this means that you're creating the tar file inside a directory that you're trying to put into the tar file. So, when tar tries to read the directory it finds the tar file as a member of the directory, starts to read it and write it out to the tar file, and so between the time it starts to read the tar file and when it finishes reading the tar file, the tar file has changed.

So for example something like:

tar cf ./foo.tar .

There's no way to "stop" this, because it's not wrong. Just put your tar file somewhere else when you create it, or find another way (using --exclude or whatever) to omit the tar file.

Answer 6

Here is a one-liner for ignoring the tar exit status if it is 1. There is no need to set +e as in sandeep's script. If the tar exit status is 0 or 1, this one-liner will return with exit status 0. Otherwise it will return with exit status 1. This is different from sandeep's script where the original exit status value is preserved if it is different from 1.

tar -czf sample.tar.gz dir1 dir2 || [[ $? -eq 1 ]]