[CentOS] Rsync and differential Backups

Mon Nov 9 17:50:52 UTC 2015
Gordon Messmer <gordon.messmer at gmail.com>

On 11/09/2015 08:01 AM, Alessandro Baggi wrote:
> how to perform a differential backup using rsync?

rsync backups are always incremental against the most recent backup 
(assuming you're copying to the same location).

> Users says diff because it copy only differences. For me differential 
> is backup from last full backup.

I don't see the distinction you're making.

rsync examines each file.  If you specify --delete, files that are in 
the destination but not the source will be removed.  Generally, files 
that match last-modified-time and size will not be copied, but flags 
like -c change the criteria for determining whether a file needs to be 
copied.  Files which do not match will be copied using an efficient 
algorithm to send the minimum amount of data (just the changes in the 
file) from the source to the destination.

> Other users says that to perform a differential backup I must include 
> in rsync command: --backup --backup-dir=/some/path but from manual 
> page of rsync:

You probably only need to use --backup-dir on systems which don't have 
GNU cp.  On systems with GNU cp, differential backups normally do 
something like:

cp -a daily.0 daily.1
rsync -a --delete source/ daily.0/

Whereas with --backup-dir, you can use rsync to do both tasks in one 
command, but your directory layout is a little messier.

> How I can perform a diff backup?

Save yourself a lot of trouble and use a front-end like rsnapshot or