a question of backup

Gustav H Meyer gustav at gcis.gov.za
Mon Feb 27 13:04:06 UTC 2006

Hi Gabriel,

On 27/02/06 13:45, Gabriel Dragffy wrote:
> Hi this mirror - non-historical backup is precisely what I want. Just wanted 
> to ask you what the part "--delete" does? I don't want to delete the contents 
> of my /home.

Please read the man pages for rsync!!! rsync is very powerful and 
please don't hold me responsible for any loss of data.

See: http://samba.org/rsync/

Got the following from the man page:

This tells rsync to delete any files on the receiving side that 
aren’t on the sending side. Files that are excluded from transfer 
are excluded from being deleted unless you use --delete-excluded.

This option has no effect if directory recursion is not selected.

This  option  can be dangerous if used incorrectly!  It is a very 
good idea to run first using the dry run option (-n) to see what 
files would be deleted to make sure important files aren’t listed.

If the sending side detects any I/O errors then the deletion of any 
files at the destination will be automatically  disabled.  This is 
to prevent temporary filesystem failures (such as NFS errors) on the 
sending side causing  a  massive  deletion  of  files  on  the 
destination.   You  can  override  this  with  the --ignore-errors 

> But also will it copy ALL of the files each time it is run or will it compare 
> the source and destination and just update where necessary?

rsync features (http://samba.org/rsync/features.html)
rsync is a file transfer program for Unix systems. rsync uses the 
"rsync algorithm" which provides a very fast method for bringing 
remote files into sync. It does this by sending just the differences 
in the files across the link, without requiring that both sets of 
files are present at one of the ends of the link beforehand.

I use rsync extensively and wish that all open source software 
repositories where available via rsync but at the same time I can 
see why it is not used. It requires processing power on the local 
and the remote side and is thus open for abuse.


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