Backup Script Using tar

3rods · 03-25-2008, 03:44 PM

I was working on a script that would mount a shared folder from my XP box, tar the contents of the share and then unmount the share. If there are any errors, it should email me (I know this isn't handled properly yet, but it sorta works).

Tar keeps exiting with a 1 because of a "tar: file changed as we read it" error. Tar still completes the archive and it looks correct (haven't MD5'd it yet), but it screws my script up.

Am I doing something wrong or is CIFS screwing me up or what? I don't want to ignore errors from tar in my script, but I don't want false positive emails either.

The script below is very rough.

Code:

#/bin/bash

PROGNAME=$(basename $0)

function error_handle
{
        if [ "$?" = "0" ]; then

        echo $?

        else

        echo "${PROGNAME}: ${1:-"Unknown Error $LINENO "}" > /storage2/picture_backups/errorlog.txt

        /usr/sbin/sendemail -f XXXXXXXX@comcast.net -t backups@XXXXXX.com -u Backup Script Error `date +%Y_%m_%d_%H_%M` 
-s smtp.XXXXXXX.net -o message-file=/storage2/picture_backups/errorlog.txt

        exit 1


        fi
}

mount -t cifs -o username=USERNAME,password=PASSWORD,ro //192.168.1.131/Pictures/PICTURES /storage2/temp > /dev/null & EPID=$!

wait $EPID

error_handle

tar -czvf /storage2/picture_backups/backup-`date +%Y_%m_%d_%H_%M`.tar.gz /storage2/temp/ >/dev/null & EPID=$!

wait $EPID

error_handle

umount /storage2/temp

error_handle

Any help would be, well, helpful.

Thanks.

druuna · 03-26-2008, 09:47 AM

Hi,

The 'error' tar is giving you tells you that a file that is being tarred is changed. You are probably tarring files that are still open/written to. Depending on what is written to these file(s) you could see this as an error, most often it should be seen as informational (next backup the 'missed' data will be tarred).

BTW: It should be #!/bin/bash, not #/bin/bash.

Hope this helps.

chrism01 · 03-27-2008, 02:24 AM

You should be doing a numerical comparison ie not

if [ "$?" = "0" ]; then

but

if [[ $? -eq 0 ]]
then

http://www.tldp.org/LDP/abs/html/comparison-ops.html

3rods · 03-27-2008, 01:43 PM

This is only my second shell script, so thanks for the help.

I still don't understand why/how the files are being changed. No person (or process) should be accessing the picture folder on the XP share. Is there a way to have tar suppress non-fatal messages so the script logic can proceed as planned?

Ellyll · 03-08-2014, 02:42 AM

I know it's an old thread, but in case it's still useful to someone, you can also use --ignore-failed-read with tar if you get the "file was changed as we read it" problem.

Ellyll · 03-08-2014, 03:45 AM

My mistake, it doesn't actually solve the problem

I guess it means it only doesn't give an error for files it cant actually open for reading.

Ellyll · 03-08-2014, 05:18 AM

It seems --ignore-failed-read worked for old versions of tar but the behaviour changed. Doesn't look like there's much you can do until you're on tar 1.27, in which case you might be able to do something with --warning=file-changed (sadly I only have 1.26 on my Debian 7 system so I've not tried it).