rsync approach

[Doug Hardie]

On 27 May 2009, at 15:03, prad wrote:

> we have 2 static ip addresses with a machine running 7.2 connected to
> each.
>
> one is the primary server, while the other does only dns and receives
> bkp dumps from the first.
>
> we want to set things up so the 2nd can be brought on line at a  
> moment's
> notice.
>
> therefore, we are thinking of rsync to duplicate 1st > 2nd (with the
> exception of rc.conf and a few other files of course because we don't
> want them to be absolutely identical).
>
> we plan to allow root login and have disabled all password access so
> that rsync can preserve permissions.
>
> is this a good way to accomplish the bkp job?

It might be, but its difficult to say without knowing a lot more about  
what going on in the system.  For example, rsync of large files that  
change real often can be an issue.  You may get an inconsistent copy  
of the file if it is changing during the update of that file.  Rsync  
does one file at a time.  Hence if you have multiple files that need  
to be consistent between them it might not happen.  If transactions  
changing a file occur between the rsync of the first file and the  
rsync of the second file, they will not be consistent.

I use rsync for basically the same thing you are considering.   
However, in my situation, the real dynamic files are database files.   
I don't rsync them.  Those are exported every evening and those files  
are rsync'd.  During the day, every application that updates a  
database file also adds a copy of the new record to the end of a log  
file.  That log file is also rsync'd about every 5 minutes.  In this  
way I can recover to within 5 minutes quite easily.  The last 5  
minutes might be a bit more work, but the information would be  
available from the original sources at that point.

Allowing root login is generally not a great approach.  Rsync will  
retain permissions (use -p) if the user id's and group ids are the  
same on both systems.  You may have to modify some of the pam files to  
permit rsync to function easily.  The easy test is to

	rsh <other host> date

If that works and you get the date, then rsync will function  
properly.  If not you need to track down why in the various log  
files.  I had to make the following change:

pam.d/rsh:

-auth   required        pam_rhosts.so   no_warn
+auth   required       pam_rhosts.so   no_warn    allow_root

This was first done quite a few years ago and has been propagated to  
the current systems so I don't know if its still required or not.

Our systems only have 3 users (the administrators) so we have  
passwords working fine.  It has not interfered with rsync.