Question

I wanted to make an incremental backup with tar.
I have made a full backup on 2012-04-08 and later I wanted to backup all files created or changed after that date.

So I did something like this:

cd /directory/I/wanted/to/back/up
tar --newer 2012-04-08 -cvnf "/backup/dir/$(date +%F).tar"

After a while I realised that tar is archiving files that I know have not changed since last backup. I checked their modification dates and they should not be included.

I coudn’t believe it so I made a little test:

cd ~
mkdir test
cd test
touch -t 201101010000 OLD
touch NEW
cd ..
tar -N 2012-01-01 -cvf test.tar ./test/*
tar -tf test.tar
ls -o ./test/

It clearly seems that tar is ignoring the -N, –newer and –after-date options. It has archived both files, even though the one I named OLD was created with a timestamp before 2012.

How can I help myself with this?

Answer 1

Your date format must be

tar --newer 20120408

for newer files than Apr 8, 2012. No “-“!

Or you can use

TWODAYSAGO=`(date --date '2 days ago' --rfc-3339=seconds)`
tar -cz  --newer-mtime="${TWODAYSAGO}"  -f bakfile.tgz  /dir_to_backup