tar Incremental Backup Not Working

I've written a bash script that does tar incremental backup on specific directories. A full backup works fine. I don't know what I'm doing wrong but when I specify an incremental backup, a full backup is done instead in the incremental directory. Perhaps some new eyes can see what I am missing. TIA.

#!/bin/bash
#
# backup for git and pit user directories
#
user=`whoami`
if [ "$user" != "root" ] ; then
	echo "must be run as root (sudo)"
	exit -1
fi
if [ `mount|grep /Backups|wc -l` -ne 1 ] ; then
   echo "Mounting backup share"
   mount /Backups
   if [ `mount|grep /Backups|wc -l` -ne 1 ] ; then
      echo "Backup skipped - backup share cannot be mounted"
      exit -1
   fi
fi
DIR1=/home/pi
DIR2=/home/git
DIR3=/usr/local/bin
META1=/Backups/pi.sngz
META2=/Backups/git.sngz
META3=/Backups/usr.sngz
DATE=$(date +%-Y%-m%-d)-$(date +%-T)
if [ $# -gt 0 ] ; then
   TYPE=$1
else
   TYPE="full"
fi
if [[ "$TYPE" == "full" || "$TYPE" == "incremental" ]] ; then
   echo "Backup type is $TYPE"
else
   echo "Usage: $0 full|incremental"
   exit -1
fi
if [ "$TYPE" == "full" ] ; then
   rm $META1
   rm $META2
   rm $META3
   rm /Backups/full/*
   rm /Backups/incremental/*
fi
OUTDIR=$1
OUT1=/Backups/$OUTDIR/pi-$DATE.tgz
OUT2=/Backups/$OUTDIR/git-$DATE.tgz
OUT3=/Backups/$OUTDIR/usr-$DATE.tgz
echo "Backing up $DIR1 to $OUT1"
tar --listed-incremental=$META1 -czf $OUT1 $DIR1
echo "Backing up $DIR2 to $OUT2"
tar --listed-incremental=$META2 -czf $OUT2 $DIR2
echo "Backing up $DIR3 to $OUT3"
tar --listed-incremental=$META3 -czf $OUT3 $DIR3

Some things to look at:

There are a few syntax errors in your script.

It is considered bad practice these days to use backticks. Use $() instead.

Valid exit codes are 0-255. Anything 1+ is considered an error.

OUTDIR=$1 could be blank if no command line arguments are used since the default is full. Maybe use OUTDIR=$TYPE
That would cause your full tgz files to be written to /Backups and not /Backups/full if not careful. Been a long time since I've played with incremental backups and looked at the listed-incremental file but it could be looking in this case in the wrong directory and therefore since it is empty create a full backup anyway.

Simpler to use grep -c /backups instead of grep /backups | wc -l or maybe use findmnt /backups and check if the string is empty.

It would make more sense to check if the uid = 0 versus username = root but that might be nitpicking.

You might want to add a test case to see of a full backup already exists when using incremental. While it should not happen during normal operations this could lead to confusion while testing...

I would try:

if [ "$#" -gt 0 ] ; then
TYPE=$1
else
TYPE="full"
fi

------------------
Steve Stites

I would always check my shell script with: www.shellcheck.net

TYPE="${1:-missing}"
case ${TYPE} in
    full) ...
    incremental) ...
    *)  # something went wrong
esac

looks a bit better for me.

Also I would add set -xv at the beginning of the script to see what's happening.

Thanks for all the suggestions (I'll implement them) but none of it addresses the root problem of tar not doing an incremental backup.

Have you tried running your tar commands separately from your script as a full and incremental backup? Does it work?

Using set -xv as suggested in your script might reveal where some subtle problem.

Nothing obvious is wrong in the actual tar commands but I have not tried simulating your full script.

Yes, it works from command line. I echoed the resulting tar command then copy/pasted it and it worked. So there seems to be something happening when run from the script.

that's why set -xv may help. It will print all the commands as they executed.
Also better coding may help you to understand what was really happened. Probably you missed a command (to put into this script) [a cd somewhere or similar] ???

I guess one of the suggested changes, although seemingly unrelated, fixed something. It is now working. I'm scratching my head but I'm not going to argue with success. Thanks for the help.

Please mark the thread as solved (if desired) using the thread tools pull down menu at the top.

Originally Posted by gw1500se I guess one of the suggested changes, although seemingly unrelated, fixed something. It is now working. I'm scratching my head but I'm not going to argue with success. Thanks for the help.

My diagnosis of the problem is that one of your if statements was not working properly. No matter what value you put on the first positional parameter the TYPE="full" value was set. By comparing the value of $# instead of the literal $# the if statement began to work correctly.

--------------------
Steve Stites