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I am mainly a MAC user. With the new Leopard, I was introduced to the wonderful Time Machine backup concept.

Read some about it on the internet and it seems a very smart way to perform periodic backups. The idea is to make a full backup of a given set of files and if the file is unchanged, the program just makes a hard link to the previous backup, saving time and space. Since Time Machine is designed for MAC, I searched for a solution in Linux environment. I didn’t have to search long to find out that rsync is the master utility to accomplish such task.

I start studying rsync and I can say I know close to nothing about it But so far I grasped the basic idea that enabled me to craft a bash script to manage my backups. So far I am so impressed with it, that I decided to share this “excitment” with anyone out there in the look-out for the perfect backup solution. Rsync is great also because it allows to perform backups over the network using secure shell (ssh) as the prefered method of connection/ authentication, therefore making it flexible, powerful and easy to use.

The man page for rync is very complex, unveiling the true power of the utility. Most probably you won’t use most of the options on the day-to-day basis, but it’s a good point of reference and memory refreshing.

The script you’ll see bellow was created for linux, but I’m using it very successful on my MAC. Currently I’m backing up my remote website data, to my external hard drive connected to my MAC laptop. I created a cron job (yes, MAC also have cron) that looks like this:

30 0,3,6,9,12,15,18,22 * * * /Users/marian/bin/backup.sh hourly > /dev/null 2>&
10 13 * * * /Users/marian/bin/backup.sh daily > /dev/null 2>&
10 23 * * 6 /Users/marian/bin/backup.sh weekly > /dev/null 2>&1
0 21 1 * * /Users/marian/bin/backup.sh monthly > /dev/null 2>&1
40 22 1 12 * /Users/marian/bin/backup.sh yearly > /dev/null 2>&1


The backup.sh script looks like this:

The script might seem “hairy” at first, but is just a bunch of conditional statements to make sure the backup run smoothly unattended. If you are to accomplish the same task at the command line (not using a script), you would only enter one line. Something like this:

rsync --exclude-from /some/path/excludes.txt --link-dest=/dest/dir/hourly.0 /source/dir/ /dest/dir/hourly.latest/ 2>&1 | tee -a log.txt

I hope this helps someone.

Have you ever created a cron job for a script to run at a certain time and you found yourself wondering if the script is runnig OK and what’s the status?

Well, a solution I found working very nice, is creating a screen (vezi man for GNU screen) session and run your script in it. You can then attach to the screen session and check out what the script is doing.

Basically, your script must do the following:

1) Check if it exists a screen session

2) If it exist, send the job to one if it’s windows

3) If it doesn’t exist, create it and then send the job to one of it’s windows.

This is not a tutorial on how to use screen. There are plenty of tutorials out there. I’m just reminding the command to send a command to a screen session from outside of it:

screen -S <sessionname> [ -p <windownumber> ] -X <command>

one very useful command is stuff which sends a string of text to the shell inside the screen. If the string is a shell command, insert a new line to execute it. See bellow a script I created to start wake me up in the morning. All it does, it starts the “europafm” script inside a screensession named “wakeupsession”.

#!/bin/bash -xf
# This script will start playing a script (~/bin/europafm) that plays radio
# inside a screen session named "wakeupscreen"
# First, check if the wakeupscreen session exists.
# If it does, use it. If not, create one.
PID=~/tmp/screen.pid
ps -fe | grep -v grep | grep wakeupscreen > $PID
if [ -s $PID ]; then
        screen -X -S wakeupscreen stuff "~/bin/europafm
"
else
        screen -d -m -S wakeupscreen
        screen -X -S wakeupscreen stuff "~/bin/europafm
"
fi

Note the new line generated the quotations on the next line.

Instead of the europafm script, you can run any script. Like a rsync backup for instance.