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,

• the tar package is ok when the warning comes up
• but it stops the tar command for the following backup
• the file showing the warning in fact doesn't change -- it is really strange that the warning comes up
• the files showing the warning come up randomly, I mean, everytime I run my makefile, the files showing the warning are different
• --ignore-failed-read doesn't help. I am using tar 1.23 in MinGW
• I just changed my computer to WIN7 64 bit. The script works well in old WIN7 32 bit. But the tar version is not as new as the 1.23.

How can I stop the tar's warning to stop my backup following the warning?

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Edit-2: it might be the reason

As I said above, the bash shell script worked well in my old computer. Comparing with the old computer, the msys version is different. So is the version of tar command. In the old computer, tar is 1.13.19 and it is 1.23 in the new computer. I copied the old tar command without copying its dependency msys-1.0.dll to the new computer and renamed it tar_old. And I also updated the tar command in the shell script and run the script. Then everything is ok. So, it seemed that the problem is the tar command. I am sure that there is no any file changed when taring. Is it a bug for tar command in new version? I don't know.

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Edit-1: add more details

The backup is invoked by a bash shell script. It scans the target directory and builds makefile then invokes make to use tar command for backup. Followed is a typical makefile built by the bash shell script.

#--------------------------------------------
# backup VC
#--------------------------------------------
# the program for packing
PACK_TOOL=tar

# the option for packing tool
PACK_OPTION=cjvf

# M$: C driver
WIN_C_DIR=c:

# M$: D driver
WIN_D_DIR=d:

# M$: where the software is
WIN_PRG_DIR=wuyu/tools
# WIN_PRG_DIR=

# where to save the backup files
BAKDIR=/home/Wu.Y/MS_bak_MSYS

VC_FRAMEWORK=/home/Wu.Y/MS_bak_MSYS/tools/VC/VC_framework.tar.bz2
VC_2010=/home/Wu.Y/MS_bak_MSYS/tools/VC/VC_2010.tar.bz2

.PHONY: all

all: $(VC_FRAMEWORK) $(VC_2010)

$(VC_FRAMEWORK): $(WIN_C_DIR)/$(WIN_PRG_DIR)/VC/Framework/*
    @$(PACK_TOOL) $(PACK_OPTION) "$@" --ignore-failed-read /c/$(WIN_PRG_DIR)/VC/Framework
$(VC_2010): $(WIN_C_DIR)/$(WIN_PRG_DIR)/VC/VS2010/*
    @$(PACK_TOOL) $(PACK_OPTION) "$@" --ignore-failed-read /c/$(WIN_PRG_DIR)/VC/VS2010

As you can see, the tar package is stored in ~/MS_bak_MSYS/tools/VC/VC_2010.tar.bz2. I run the script in ~/qqaa. ~/MS_bak_MSYS is excluded from tar command. So, the tar file I am creating is not inside a directory I am trying to put into tar file. This is why I felt it strange that the warning came up.

Answer 1

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