Creating Snapshots in Linux / MacOSX

Here is a script I wrote back in the 1999 time frame to perform daily, weekly, monthly snapshots of critical directories.  This scripts is designed for filesystems that support the notion of hard links, aka Linux and MacOSX. (The Windows filesystems do not support hard links and thus this will not work on Windows).

This script is usually called from /etc/crontab and requires that you have rsync installed on the system.  At the top of the actual script code is a section that you will need to update to specify where you want the backups to go and what directories you want to backup.

#!/usr/bin/perl
#
#
####################################################################
# Ideas taken from Mike's handy rotating-filesystem-snapshot       #
# utility, http://www.mikerubel.org/computers/rsync_snapshots/     #
# and from code written by Eric Ross                               #
####################################################################
#
####################################################################
# This program is not guaranteed to work at all, and by using this #
# program you release the author of any an all liability.          #
#                                                                  #
# You may use this program so long as this notice, disclaimer and  #
# comment box remain intact and unchanged.                         #
#                                                                  #
# Please send me all bugs and patches.                             #
#                                                                  #
# Written by Bret Jordan                                           #
# jordan at open1x littledot org                                   #
####################################################################
#
#
#
# Example /etc/crontab
# Every night at 1:01 make rsync copy and then give plenty of time before snapshots
# 01 1  * * *     root  /local/bin/snapshot rsync
#
# Every night at 2:01 make snapshots
# 01 2  * * *     root  /local/bin/snapshot snap 7 daily
#
# Every Sunday Morning at 3:01 make weekly snapshot
# 01 3  * * 7     root  /local/bin/snapshot snap 4 weekly
#
# First day of every month at 4:01 make monthly snapshot
# 01 4  1 * *     root  /local/bin/snapshot snap 12 monthly


use 5.8.8;
use strict;
use warnings;

our $VERSION = "0.02";
$VERSION = eval $VERSION;

my $sType = shift;
my $iHistoryLength = shift; 
my $sFreq = shift;


########################
# BEGIN THINGS TO UPDATE

my $sSnapDir = "/backups/snapshots";
my $sCurrentBackupDir = "$sSnapDir/backup.current";
my @aDirsToBackup = qw (/data/home/);

# END THIGNS TO UPDATE
########################


unless ($sType eq "rsync" || $sType eq "snap")
{ &ShowSyntax(); }


if ($sType eq "snap")
{
    unless ($iHistoryLength =~ /^\d+$/) 
    { &ShowSyntax(); }

    unless ($sFreq eq "hourly" || $sFreq eq "daily" || $sFreq eq "weekly" || $sFreq eq "monthly") 
    { &ShowSyntax(); }
}


sub ShowSyntax
{
    print "Please run command with ./snapshot <rsync snap=""> <historylength> <freq name="">\n";
    print "Example: ./snapshot 7 daily\n";
    print "Example: ./snapshot 24 hourly\n";
    die;
}

# Lets make sure we are running at root
unless ( $< == 0 ) { die "This program must be run as root\n"; }

# Do we have write access to the snap directory?
unless ( -w $sSnapDir ) { die "This user does not have write access to $sSnapDir\n"; }


if ($sType eq "rsync") 
{
    #----------------------------------------
    # Rsync Command
    #----------------------------------------
    #-a = archive mode which is -rlptgoD (no -H,-A,-X)
    #
    #-r = recurse in to directories
    #-l = copy symlinks as symlinks
    #-p = preserve permissions
    #-t = preserve modification times
    #-g = preserve group
    #-o = preserve owner
    #-D = preserve device files and special files

    foreach (@aDirsToBackup) { system("rsync -vax --delete $_ $sCurrentBackupDir"); }

    # Touch the directory so the date time is right
    system("touch $sCurrentBackupDir");
}
elsif ($sType eq "snap")
{
    # Step 1: Delete oldest snap shot and increase the age of the rest
    my $i = $iHistoryLength;
    while ($i > 0)
    {
    my $sCurrentDir = "$sSnapDir/backup.$sFreq.$i";

    # If index equals the max length of the history, then delete that directory
    if ( $i == $iHistoryLength ) { system ("rm -rf $sCurrentDir"); }
    else 
    {  
        my $j = $i + 1;
        my $sNewDir = "$sSnapDir/backup.$sFreq.$j";
        if ( -d $sCurrentDir ) { system ("mv $sCurrentDir $sNewDir"); }
    }
    $i--;
    }

    # Step 2: Make a hard link from the backup.current to backup.daily.1
    unless ( -d $sCurrentBackupDir ) { die "The current backup directory does not exist\n"; }
    system("cp -al $sSnapDir/backup.current $sSnapDir/backup.$sFreq.1");
}