When inode change time changes?

[Oliver Fromme]

Artem Kuchin wrote:
 > Also, i use inode time because i only need files
 > which really have been changed. For example,
 > i you restore a file from a month ago it will have
 > a date which is a month ago. Then that backup
 > is destroyed but this file would not be backed up
 > because the date is too  much in the past. So, we
 > loose the file. If i used inode change time the file
 > will be backup in any case. However, some 
 > "stupid" programs like mysql or qmail seem to
 > touch files so,

Pretty much _any_ operation on a file (except reading it)
will update the ctime of the inode.  So I'm not surprised
that the ctime of database files and mail files gets
updated often.

(However, I do agree that mysql and qmail are "stupid",
but for entirely different reasons. ;-)

 > for example, all mail message and
 > databases are backed up every time. And this sucks.

Seems like you need to make a distinction:  Use mtime
for /var/mail and /var/db/mysql/data (or wherever your
db files are), and use ctime for everything else.

With find(1) and bsdtar(1) that's pretty easy:

# set -f        # disable shell-expansion of "*"
# MDIRS="( -path ./var/mail/* -o -path /var/db/mysql/data/* )"
# FLAG="/var/db/lastbackup.flag"
# find . $MDIRS -mnewer $FLAG -o ! $MDIRS -cnewer $FLAG \
  | tar -cn -T- -f- | gzip -c > $DESTINATION.tar.gz

However, as you pointed out, it will not record the fact
that a file has been deleted since the last level-0 backup,
so it's not a perfect incremental backup.  (However, it's
sufficient for me personally.  Another solution would be
to store the output from "find" along with the level-1
backup, so you can easily find out what files didn't exist
anymore when you restore the backup.)

You might also use the "-print0" flag on find(1) and the
"--null" flag on tar(1) if there's the possibility that
file names could contain whitespace ...  I omitted some
details for brevity.

Anyhow, it's just a suggestion.  It works perfectly fine
for me, but it might not work for you.  YMMV.

 > What is still do not understand is what time gtar  uses for
 > --newer option.
 > 
 > Man page says:
 > 
 > --newer date            Only store files with creation time newer than
 >                         date.
 > 
 > This is simply not true. NOT creation time defenetly.

Sure?  Did you test it?

 > It is either modification time or inode change time. Which one?

You can either simply test it by creating a few test files
and making a test archive.  Or look it up in the source
code of gtar.  I don't have gtar installed so I can't tell.

Best regards
   Oliver

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