Using rsync to enable automatic backup MX mail server domains

Seems like it might be as easy as creating a script that looks like this:
rsync -e ssh -avz root@primaryserver:/etc/localdomains /tmp/secondarymx
cat /etc/secondarymx >>/tmp/secondarymx
cat /tmp/secondarymx |sort |uniq >/tmp/secondarymx.new
mv /tmp/secondarymx.new /etc/secondarymx
rm /tmp/secondarymx



Then, put that script in cron and it should do what you want. Mine is probably not the only way to go, and there may be ways to optimize, but that's what I can pull out of my head at the moment.

 

rsync does have an append fucntion, but it doesn't do what you think. Here is the man page excerpt:
--append
This causes rsync to update a file by appending data onto the
end of the file, which presumes that the data that already
exists on the receiving side is identical with the start of the
file on the sending side. If that is not true, the file will
fail the checksum test, and the resend will do a normal
--inplace update to correct the mismatched data. Only files on
the receiving side that are shorter than the corresponding file
on the sending side (as well as new files) are sent. Implies
--inplace, but does not conflict with --sparse (though the
--sparse option will be auto-disabled if a resend of the
already-existing data is required).

So, essentially, it is just another, more bandwidth efficient method to transfer the whole file.

Note: my rough script above would not remove a domain that was deleted from secondarymx on primaryhost. Otherwise, I think it'll work too.