A simple autotmated backup system.

ssh+rsync+cron is a good combination for backup.

Let us take a simple scenario like this

	Main System	Backupsystem
hostname	server	backup
userid	myid	bup
directory	/home/data	/home/backup/data

Other constraints/conditions

a.should be done everyday at 10.30am

b.should be automatic without manual intervention.

Let us do it step by step

Stage 1: Establishing passwordless ssh connection

On server

Login as user

Generate key pairs

myid@server$ ssh-keygen -t rsa

Now .ssh directory will have a file named id_rsa.pub. This is the public key of user myid. Copy this file to backup system using scp.

myid@server$ scp .ssh/id_rsa.pub bup@backup:~/.ssh/server.pub

Enter Password:

Now log onto backup system

myid@server$ ssh bup@backup

bup@backup$ cd .ssh

bup@backup$ cat server.pub >>authorized_keys2

ensure that files in .ssh has read/write for owner and no permission for others and group.

Now log out of backup. You will be back at server.

myid@server$

Now try to login again on backup. You will not be prompted for password.

Stage 2: Creating appropriate rsync command

First let us try the rsync at command prompt in the server.

myid@server$ rsync -e ‘ssh -l bup’ -avzp /home/data/ backup:/home/backup/data

Let me explain the command in detail.

-e option allows rsync to use ssh. Rsync can use its own protocol or rsh or ssh. Here we choose ssh and give the options to ssh like -l login name inside a single quote.

-a this option lets rsync to work in archive mode, so files are copied recursively much like tar.

-v verbose gives details about files transferred

-z use compression

-p preserve permission.

While using rsync the distinction between with and without a / at the end is important when specifying source. If last / is omitted it will create a directory and then copy.

Stage 3:Converting rsync into cron job.

Store the above command in a file say mybackup.sh

myid@server$ cat mybackup.sh

rsync -e ‘ssh -l bup’ -avzp /home/data/ backup:/home/backup/data >>/home/myid/errorlog 2>&1

Here I am directing all messages to myid/errorlog file.

Grant executable permission

myid@server$ chmod u+x mybackup.sh

Now add it to cron

myid@server$ crontab -e

30 10 * * * /home/myid/mybackup.sh >>/home/myid/errorlog 2>>/home/myid/errorlog

In the above line 30 stands for minute and 10 stands for hour. Normally cronjob errors are directed to mail, but we can redirect as done above also.

If everything proper you should have a fully automated backup which is very fast also.

Addon features

a.You can schedule backup more than once say every hour.

b.Improve the shell script for multiple backup depending on date and time

c.Start the backup system through wake on lan, take backup and then shutdown.