Better Backups With Tar

Many professional users still lose information due to lack of making good computer file backups, yet Linux provides powerful tools that can help you make backups easily and automatically.

The example script on this page is an improvement of Chapter33.3. Automating backups with tar which shows a basic, yet, effective backup script (Chapter 33 has several other good ideas too).

If you understand how scripts work and are confident with being able to modify one, then you can modify the one shown below to meet your particular circumstances and create an effective, automated backup for yourself and/or custom backups for other users.

The improvements in this script are:

As is mentioned in Chapter33.3. Automating backups with tar, it is also recommended to run this script at the beginning of the month for the first time, then insert the script in the /etc/cron.daily/ directory afterwards and let it run for a month automatically before making any major changes.


In the script example shown below, we backup 3 different directories to a backup directory on a local server.

  1. First, create the backup script backup.cron file as shown below so that you can test it out manually. Make sure to use directories 1, 2, 3 according to what you need (this example backs up the directories "/home/bird", "/home/cat", "/home/dog" ).
    # full and incremental backup script
    # created 07 February 2000
    # Based on a script by Daniel O'Callaghan <>
    # modified by Gerhard Mourani <>
    # modified by Jose Da Silva <> 05/feb/08
    # (add continuous 4 week backup so you can recover further back)
    # modified by Jose Da Silva <> 08/sep/10
    # (add error checks, no chown/chmod if filesystem not compatible)
    # modified by Jose Da Silva <> 12/oct/16
    # (separate monthly dir, split for DVD, CD, or TAPE. --exclude=)
    # This script was originally based on the script shown on website
    # <> and was
    # modified to backup several directories plus keep a "lastweek"
    # "prevweek" and "priorweek" backups too, and report errors.
    # This script was further improved with additional requests asked
    # by readers looking for a basic backup script, such as reporting
    # of basic errors, such as failing to save, allowing backups on
    # filesystems without UNIX-like ownership permissions, and making
    # monthly backups in a segmented fashion which is portable enough
    # to be backed up to media such as TAPE, CDrom, or DVDrom to be
    # kept off-site elsewhere. To restore segmented backups, you will
    # need to join the files as "cat backup.tar.gz.* >backup.tar.gz"
    # If you need to backup directories which contain active files,
    # it is recommended that you do a snapshot of those directories
    # and then do a backup of the snapshot, this way, you have less
    # problems dealing with file-locks and files in transition.
    # If you need to run a snapshot first, just insert a call to the
    # appropriate script at the beginning/end of the main routine below.
    # Change the variables below to fit your computer/backup system
    COMPUTER=genesis		# Name of this computer
    DIR1="/home/bird /home/cat"	# Directories to backup daily
    DIR2="/home/dog"		# (only 3 examples shown here, but
    DIR3="/etc /root"		#  more can be added DIR4, DIR5...)
    # (Add more DIRX and modify code down in main routine as needed)
    # Exclude these files and directories from the tar backup files
    EXL1="--exclude='*.kde4/cache-* *.kde4/socket-* *.kde4/tmp-*'"
    EXL2="--exclude='*~ *.bak *.BAK'"
    BKDIR="/backups"		# Where to store daily backups
    BKDIRM="/backupsM"		# Where to store monthly backups
    BKSIZM="638m"			# Size of monthly backups, 0=off
    TIMEDIR="$BKDIR/last-full"	# Where to store full backup "time"
    ERRFILE="/var/log/syslog"	# Send error messages to this file
    BKOWNER=root.adm		# Owner and Group for backup files
    CHMODCHOWN=1			# These files use chmod+chown, 0=off
    # Reduce list of paths to trusted directories (most->least trusted)
    # Name and location of commands so you don't need to search paths
    TAR=/bin/tar			# Name and location of commands
    BASENAME=/bin/basename		# Use "which" to find commands, but
    CAT=/bin/cat			# try to check /bin before using
    DATE=/bin/date			# commands located elsewhere such as
    ECHO=/bin/echo			# in /usr/local/bin or in /usr/bin
    DOW=`$DATE +%a`			# Day of the week e.g. Mon
    DOM=`$DATE +%d`			# Date of the Month e.g. 27
    MD=`$DATE +%b%d`		# Month and Date e.g. Sep27
    MDT=`$DATE +"%b %d %T"`		# Month Day Time Sep 27 12:00:00
    CMD=`$BASENAME "$0"`		# Command Line Program
    EM="$MDT `$HOSTNAME` $CMD[$$]:"	# Error Message info
    errortmp=0			# Temporary error accumilator
    errors=0			# 0 if no errors found at all
    # On the 1st of the month, do permanent full backups.
    # If BKSIZM=0, then make one large backup file, otherwise break the
    # monthly backups into segments which can be put on CDroms (638m),
    # or DVDroms, or Tape, or another offsite backup media. This is
    # done by making a complete file, and then splitting the file into
    # seperate segments that can be retrieved or moved at a later time.
    # Every Sunday, prevweek's backup is pushed to priorweek's backup,
    # lastweek's backup pushed to prevweek's backup, and then Sunday's
    # backup is pushed to lastweek's backup before creating a Sunday
    # full backup. This creates 4 weeks worth of rollover backups.
    # Monday to Saturday, an incremental backup is made based on Sunday
    # so that you you have daily backups for new files until next week.
    # if NEWER = "", then tar backs up all files in the directories
    # otherwise it backs up files newer than the NEWER date. NEWER
    # gets its date from the file written every Sunday.
    ErrorTest () {
      # Check exit status of last command for any errors and set flag
      if [ "$?" -ne 0 ]; then
    ErrorSet () {
      # Set errors if errortmp=1 and send error message to $ERRFILE
      if [ $errortmp -eq 1 ]; then
        $ECHO "$EM Error $1" >> $ERRFILE;
    UpdateTheDate() {
      # Update full backup date so increments happen after this
      NOW=`$DATE +"%Y-%m-%d %X"`; ErrorTest;
      $ECHO "$NOW" > "$TIMEDIR/$COMPUTER-full-date"; ErrorTest;
      if [ $CHMODCHOWN -eq 1 ]; then
        $CHMOD 640 "$TIMEDIR/$COMPUTER-full-date"; ErrorTest;
        $CHOWN $BKOWNER "$TIMEDIR/$COMPUTER-full-date"; ErrorTest;
      ErrorSet "with time stamp $TIMEDIR/$COMPUTER-full-date";
    MakeFullMonthlyBackup() {
      # Make a full monthly backup based on given directories.
      # Store the monthly backup in directory location BKDIRM
      if [ -z $BKSIZM ] || [ "$BKSIZM" == "0" ]; then
        # Save one large backup file into monthly backup directory
        $TAR $3 -cpzf "$BKDIRM/$COMPUTER-$MD-$1.tar.gz" "$2"; ErrorTest;
        if [ $CHMODCHOWN -eq 1 ] && \
           [ -f "$BKDIRM/$COMPUTER-$MD-$1.tar.gz" ]; then
          $CHMOD 640 "$BKDIRM/$COMPUTER-$MD-$1.tar.gz"; ErrorTest;
          $CHOWN $BKOWNER "$BKDIRM/$COMPUTER-$MD-$1.tar.gz"; ErrorTest;
        # Create one large backup file temporarily that tar can verify
        $TAR $3 -cpzf "$BKDIR/$COMPUTER-$MD-$1.tar.gz" "$2"; ErrorTest;
        # Split backup file into segments that can be stored elsewhere
        if [ -f "$BKDIR/$COMPUTER-$MD-$1.tar.gz" ]; then
          # If file created then split results into monthly backup dir
          $CAT "$BKDIR/$COMPUTER-$MD-$1.tar.gz" | $SPLIT -b$BKSIZM - \
               "$BKDIRM/$COMPUTER-$MD-$1.tar.gz."; ErrorTest;
          $RM -f "$BKDIR/$COMPUTER-$MD-$1.tar.gz"; ErrorTest;
          if [ $CHMODCHOWN -eq 1 ]; then
            $CHMOD 640 "$BKDIRM/$COMPUTER-$MD-$1.tar.gz."*; ErrorTest;
            $CHOWN $BKOWNER "$BKDIRM/$COMPUTER-$MD-$1.tar.gz."*;
      ErrorSet "with tar file $BKDIRM/$COMPUTER-$MD-$1.tar.gz";
    MakeFullWeeklyBackup() {
      # Store 4 full weekly backups in directory location BKDIR
      # First, move previous week's backups into prior week's backups
      if [ -f "$BKDIR/$COMPUTER-$DOW-prevweek-$1.tar.gz" ]; then
        $MV "$BKDIR/$COMPUTER-$DOW-prevweek-$1.tar.gz" \
            "$BKDIR/$COMPUTER-$DOW-priorweek-$1.tar.gz"; ErrorTest;
        if [ $CHMODCHOWN -eq 1 ]; then
          $CHMOD 640 "$BKDIR/$COMPUTER-$DOW-priorweek-$1.tar.gz";
          $CHOWN $BKOWNER "$BKDIR/$COMPUTER-$DOW-priorweek-$1.tar.gz";
        ErrorSet "moving $BKDIR/$COMPUTER-$DOW-prevweek-$1.tar.gz";
      # Next, move last week's backups into previous week's backups
      if [ -f "$BKDIR/$COMPUTER-$DOW-lastweek-$1.tar.gz" ]; then
        $MV -f "$BKDIR/$COMPUTER-$DOW-lastweek-$1.tar.gz" \
               "$BKDIR/$COMPUTER-$DOW-prevweek-$1.tar.gz"; ErrorTest;
        if [ $CHMODCHOWN -eq 1 ]; then
          $CHMOD 640 "$BKDIR/$COMPUTER-$DOW-prevweek-$1.tar.gz";
          $CHOWN $BKOWNER "$BKDIR/$COMPUTER-$DOW-prevweek-$1.tar.gz";
        ErrorSet "moving $BKDIR/$COMPUTER-$DOW-lastweek-$1.tar.gz";
      # Then, move this week's full backups into last week's backups
      if [ -f "$BKDIR/$COMPUTER-$DOW-$1.tar.gz" ]; then
        $MV "$BKDIR/$COMPUTER-$DOW-$1.tar.gz" \
            "$BKDIR/$COMPUTER-$DOW-lastweek-$1.tar.gz"; ErrorTest;
        if [ $CHMODCHOWN -eq 1 ]; then
          $CHMOD 640 "$BKDIR/$COMPUTER-$DOW-lastweek-$1.tar.gz";
          $CHOWN $BKOWNER "$BKDIR/$COMPUTER-$DOW-lastweek-$1.tar.gz";
        ErrorSet "moving weekly file $BKDIR/$COMPUTER-$DOW-$1.tar.gz";
      # Finally, create a new weekly backup for this day-of-week
      $TAR $3 -cpzf "$BKDIR/$COMPUTER-$DOW-$1.tar.gz" "$2"; ErrorTest;
      if [ $CHMODCHOWN -eq 1 ]; then
        $CHMOD 640 "$BKDIR/$COMPUTER-$DOW-$1.tar.gz"; ErrorTest;
        $CHOWN $BKOWNER "$BKDIR/$COMPUTER-$DOW-$1.tar.gz"; ErrorTest;
      ErrorSet "with weekly file $BKDIR/$COMPUTER-$DOW-$1.tar.gz";
    MakeIncrementalWeeklyBackup() {
      # Make an incremental backup in BKDIR based on date in NEWER file
      $TAR $4 --newer="$1" -cpzf "$BKDIR/$COMPUTER-$DOW-$2.tar.gz" "$3";
      if [ $CHMODCHOWN -eq 1 ] && \
         [ -f "$BKDIR/$COMPUTER-$DOW-$2.tar.gz" ]; then
        $CHMOD 640 "$BKDIR/$COMPUTER-$DOW-$2.tar.gz"; ErrorTest;
        $CHOWN $BKOWNER "$BKDIR/$COMPUTER-$DOW-$2.tar.gz"; ErrorTest;
      ErrorSet "with incremental file $BKDIR/$COMPUTER-$DOW-$2.tar.gz";
    MakeBackupDirectory() {
      if [ $errortmp -eq 0 ]; then
        # Verify backup directory $1 exists, otherwise create it.
        if [ ! -d "$1" ]; then
          $MKDIR "$1"
          if [ ! -d "$1" ]; then
            $ECHO "$EM Error, cannot make $1!" >> $ERRFILE;
            $ECHO "$EM Error, no backup files made!" >> $ERRFILE;
            if [ $CHMODCHOWN -eq 1 ]; then
              $CHMOD 740 "$1"; ErrorTest;
              $CHOWN $BKOWNER "$1"; ErrorTest;
              ErrorSet "setting permissions on directory $1";
    #----- Main program starts here -----
    if [ ! -z $1 ] && [ "$1" != "--full" ]; then
      $ECHO "Usage: $0 --full to force a full monthly + weekly backup.";
      $ECHO "Run $0 without any command-line options to run automated.";
      $ECHO "All other variables are set in the script.";
      exit 0
    if [ "`$WHOAMI`" != "root" ]; then
      $ECHO "$EM Sorry, you must be root!";
      exit 1
    # Mount drive. NOTE: Create mount in /etc/fstab before using this,
    # otherwise you need to describe the /dev/hd_ location in here!
    #$MOUNT "$BKDIR";
    # Verify all backup directories exist, otherwise create them.
    MakeBackupDirectory "$BKDIRM";	# Build monthly directory
    MakeBackupDirectory "$BKDIR";	# Build rotating directory
    if [ $errortmp -eq 1 ]; then
      exit 2
    MakeBackupDirectory "$TIMEDIR";	# Build timekeeping directory
    if [ $errortmp -eq 1 ]; then
      exit 3
    # Verify time file exists, otherwise create it.
    if [ ! -f "$TIMEDIR/$COMPUTER-full-date" ]; then
      if [ -f "$TIMEDIR/$COMPUTER-full-date" ]; then
        # Created a new time file with current time
        if [ $CHMODCHOWN -eq 1 ]; then
          $CHMOD 640 "$TIMEDIR/$COMPUTER-full-date"; ErrorTest;
          $CHOWN $BKOWNER "$TIMEDIR/$COMPUTER-full-date"; ErrorTest;
          ErrorSet "setting permissions, $TIMEDIR/$COMPUTER-full-date";
        # Unable to create a Time file, report an error
        $ECHO "$EM Error, cannot find $TIMEDIR/$COMPUTER-full-date!" \
              >> $ERRFILE;
        $ECHO "$EM Error, no backup files made !" >> $ERRFILE;
        exit 4
    if [ $DOM == "01" ] || [ "$1" == "--full" ]; then
      # Create Monthly Backups on 1st day of each month,
      # or if user added --full on the command-line
      MakeFullMonthlyBackup "1" "$DIR1" "$EXL1";
      MakeFullMonthlyBackup "2" "$DIR2" "$EXL2";
      MakeFullMonthlyBackup "3" "$DIR3" "$EXL3";
      # ...This is only an example of stop, backup, start (a service)
      #$SERVICE boinc stop
      #MakeFullMonthlyBackup "4" "$DIR4" "$EXL4";
      #$SERVICE boinc start
    if [ $DOW == "Sun" ] || [ "$1" == "--full" ]; then
      # Create Full Weekly Backups on Sundays
      MakeFullWeeklyBackup "1" "$DIR1" "$EXL1";
      MakeFullWeeklyBackup "2" "$DIR2" "$EXL2";
      MakeFullWeeklyBackup "3" "$DIR3" "$EXL3";
      # Make incremental backups - overwrite last weeks
      # Get date of last full backup
      NEWER="`$CAT $TIMEDIR/$COMPUTER-full-date`"
      MakeIncrementalWeeklyBackup "$NEWER" "1" "$DIR1" "$EXL1";
      MakeIncrementalWeeklyBackup "$NEWER" "2" "$DIR2" "$EXL2";
      MakeIncrementalWeeklyBackup "$NEWER" "3" "$DIR3" "$EXL3";
    # Done, umount this drive until it is needed again tomorrow
    #$UMOUNT -l "$BKDIR";
    #if [ $errors -eq 1 ]; then
    #  # Errors were found while doing a backup, warn someuser!
    #  $ECHO "$EM Error creating backups!" >> \
    #	 /home/someuser/Desktop/warning.txt
    #  $CHMOD 777 /home/someuser/Desktop/warning.txt

  2. You will have to modify BKDIR to a location where you want to keep your rotating weekly backups. Right now, the script above will store your weekly backups in "/backups".
  3. You will have to modify BKDIRM to a location where you want to keep your monthly backups. Right now, the script above will store your monthly backups in "/backupsM".

    You will have to modify BKSIZM to a size you want. Right now, the script above creates a backup tar files in BKDIR, and then splits them into 638 megabyte sections which you can then copy to CDrom, or seven per DVD. Use BKSIZM=0 if you want to keep the backup as one large file (but make sure that the file system is capable of holding files equal to or greater than 2 gigabytes in size).

    Change the size to fit your needs (BKSIZM=0 turns file-splitting off). Use some caution to verify that you do not end up with corrupted backups if they are larger than 2 gigabytes since some backup location cannot save or transfer very large files.

  4. EXL1, EXL2, EXL3 can be used to add additional options such as --exclude=' '.
  5. MOUNT and UMOUNT could be useful when you have a computer with separate hard drives used for backups. You will need to set AHCI in BIOS and hdparm -S_ /dev/hd_ in Linux.
  6. Test your backup.cron file to make sure it runs. You can temporarily test the script like this sh backup.cron, but you will need to make the backup.cron file executable when it is ready to be run automatically by cron.
    [dog@genesis tmp]$ su
    Password: ***
    [root@genesis tmp]# chmod 750 backup.cron
    [root@genesis tmp]# chown root.adm backup.cron
    [root@genesis tmp]# ls -l backup.cron
    -rwxr-x--- 1 root adm 6161 Aug 8 21:00 backup.cron*
    [root@genesis tmp]# ./backup.cron

  7. Below is a quick look at the backup directory after a few test runs (the script was modified to use "08" and "Tue" as the first dates so that you can see these results shown here).
    [root@genesis tmp]# ls -l /backups/
    -rw-r----- 1 root adm     2307 Aug 8 21:21 genesis-Aug08-1.tar.gz
    -rw-r----- 1 root adm   367504 Aug 8 21:21 genesis-Aug08-2.tar.gz
    -rw-r----- 1 root adm 32094115 Aug 8 21:22 genesis-Aug08-3.tar.gz 
    -rw-r----- 1 root adm      138 Aug 8 21:47 genesis-Tue-1.tar.gz
    -rw-r----- 1 root adm     1289 Aug 8 21:47 genesis-Tue-2.tar.gz
    -rw-r----- 1 root adm     8383 Aug 8 21:47 genesis-Tue-3.tar.gz
    drw-r----- 2 root adm     4096 Aug 8 21:21 last-full/
    [root@genesis tmp]# ls -l /backups/last-full/
    -rw-r----- 1 root adm  20 Aug 8 21:21 genesis-full-date

  8. Backups is something you will do often, but you should also verify that your backups are indeed working correctly because restores are something that is seldom done yet very important to do when the time comes to restore a file (or many files). Please check Chapter 33, mentioned above, for steps on how to restore files and directories.

  9. Once you are satisfied that the script appears to run well from the command line, then the next step is to install backup.cron in the cron directory and let your computer run it automatically. You should check the /backups/ directory the next day to verify it holds backups that were made at night.
    [root@genesis tmp]# cp backup.cron /etc/cron.daily/backup.cron
    [root@genesis tmp]# chmod 750 /etc/cron.daily/backup.cron
    [root@genesis tmp]# chown root.adm /etc/cron.daily/backup.cron
    [root@genesis tmp]# ls -l /etc/cron.daily/backup.cron
    -rwxr-x---  1 root adm 6145 Aug 8 23:05 /etc/cron.daily/backup.cron*


Important things to think about when using backup.cron

You may note that doing backups with tar is a disk intensive activity, so if your computer is doing little else at one o'clock in the morning, it's perhaps best to let it finish quickly.

If your computer is a server with additional duties, you may want to add the nice -2 command to make the backup more of a background task to give other processes more priority. This will make backups take longer, but it does allow other processes to run in better priority.

You may note that both this script and the basic script mentioned in Chapter33.3. Automating backups with tar have trouble backing up files that are still in use. If this is the case, you need to add to your backup.cron script a shutdown of the process(es) that cause trouble before you do a backup of that particular directory, then restart the process(es) after tar finishes those directories (for example SQL and other live services). A quicker method to shorten the shutdown time involves taking a snapshot of the troublesome directories, restart the process(es) and making a backup of the snapshot.

Some file systems and some versions of tar are limited to output file sizes of about 2 gigabytes. Make sure you use a recent version of tar and if you find that the output file will be approaching or passing 2 gigabytes. If you need to save the backup files to a file system that cannot handle 2 gigabyte or larger files, then you will need to split the output files. This example script assumes BKDIR can handle 2 gigabyte files or greater.

If you use split then remember to use cat to join the files for restoring.


It is great if you find this backup.cron script useful, but if you can think of improvements or fixes, please send suggestions using the comment section here so that the script can be improved:

Your Name:
Your Email:
Comments / Suggestions:

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