Incremental backup with rsync

Hello World,

It's more a tip than an article but today I create a little script for you to make incremental backups using rsync.
An incremental backup is a backup that only contains modified files since the last backup. In this article I invert this principle to backup in a separate folder old versions of a modified or deleted file.

For this script we only need three options of rsync:

  • --delete for deletion of useless files in the destination folder
  • --backup to make backup of modified or deleted files in the destination folder (mandatory for using --backup-dir)
  • --backup-dir to tell to rsync which folder to use for backuped files

Note: If you don't use --delete, rsync will keep all deleted files in the destination folder.

So, the complete command is like that:

rsync -a -b --delete --backup-dir=mydir source dest

I love -a option and -b is the short option of --backup
Note: To prevent misconfiguration, you should use absolute path for --backup-dir
Note 2: You can use -z if you want to compress data during the transfer

For our incremental backup we want to backup files using the backup date, so we use date command in the rsync command, like that:

CURBCK=$(date +%Y%m%d)
ABSCURBCK=/my/path/to/$CURBCK
rsync -a -b --delete --backup-dir=$ABSCURBCK source/ dest

In this example I assume that we call this script only once a day (the backup folder is named using the form YYYYMMDD), you can replace %Y%m%d by %Y%m%d%H%M%S to be more specific (YYYYMMDDHHMMSS).

Test of this bunch of commands:

# in source folder
$ ls
file
$ sha1sum
827506be8bdb09a5f3c463ad6aa45ca66d7bccbf

# We make a sync and verify file in the dest file
$ ls
file
$ sha1sum file
827506be8bdb09a5f3c463ad6aa45ca66d7bccbf

# We modify the file and make a new sync
$ sha1sum source/file backup/**/file
c2304cf35abdb7a8c79d29737accc75de6db495a  source/file
c2304cf35abdb7a8c79d29737accc75de6db495a  backup/current/file
827506be8bdb09a5f3c463ad6aa45ca66d7bccbf  backup/20120309201330/file

# We delete the file
$ sha1sum source/file backup/**/file
sha1sum: source/file: No such file or directory
827506be8bdb09a5f3c463ad6aa45ca66d7bccbf  backup/20120309201330/file
c2304cf35abdb7a8c79d29737accc75de6db495a  backup/20120309201456/file

Feel free to add scripts to compress backup files.

Enjoy it!