通常在考虑增量备份时,需要使用tar命令备份某个日期之后的文件,而tar命令的如下参数可以满足这个需求:

-N, –after-date DATE, –newer DATE
例如,

/bin/tar –newer="2010-11-27″ -cf file.tar dir_to_backup
/bin/tar –newer 2010-11-27 -cf file.tar dir_to_backup
/bin/tar -cf file.tar dir_to_backup –newer="2010-11-27″
如果希望备份比某一个参考文件更新的文件,则可以使用如下命令:

/bin/tar –newer="`date -r refFile`" -cf tarFile.tar dir_to_backup
增量备份方法:

#!/bin/sh
# full and incremental backup script
# created 07 February 2000
# Based on a script by Daniel O’Callaghan <danny@freebsd.org>
# and modified by Gerhard Mourani <gmourani@videotron.ca>
# Change the 5 variables below to fit your computer/backup
COMPUTER=deep # name of this computer
DIRECTORIES="/home" # directoris to backup
BACKUPDIR=/backups # where to store the backups
TIMEDIR=/backups/last-full # where to store time of full backup
TAR=/bin/tar # name and locaction of tar

#You should not have to change anything below here
PATH=/usr/local/bin:/usr/bin:/bin
DOW=`date +%a` # Day of the week e.g. Mon
DOM=`date +%d` # Date of the Month e.g. 27
DM=`date +%d%b` # Date and Month e.g. 27Sep

# On the 1st of the month a permanet full backup is made
# Every Sunday a full backup is made – overwriting last Sundays backup
# The rest of the time an incremental backup is made. Each incremental
# backup overwrites last weeks incremental backup of the same name.
#
# if NEWER = “", then tar backs up all files in the directories
# otherwise it backs up files newer than the NEWER date. NEWER
# gets it date from the file written every Sunday.

# Monthly full backup
if [ $DOM = “01″ ]; then
NEWER=""
$TAR $NEWER -cf $BACKUPDIR/$COMPUTER-$DM.tar $DIRECTORIES
fi

# Weekly full backup
if [ $DOW = “Sun" ]; then
NEWER=""
NOW=`date +%d-%b`
# Update full backup date
echo $NOW > $TIMEDIR/$COMPUTER-full-date
$TAR $NEWER -cf $BACKUPDIR/$COMPUTER-$DOW.tar $DIRECTORIES

# Make incremental backup – overwrite last weeks
else
# Get date of last full backup
NEWER="–newer `cat $TIMEDIR/$COMPUTER-full-date`"
$TAR $NEWER -cf $BACKUPDIR/$COMPUTER-$DOW.tar $DIRECTORIES
fi