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Syncing Content Between RackSpace Cloud Servers With Unison

We have two RackSpace Cloud Server running CentOS that need to have the web content kept in sync. Changes on either server need to be replicated to the other server. Easy way to get this accomplished is with the Unison File Syncronizer ( Here are the steps:

1. Install SSH keys for root on each server so SSH can run without passwords between the servers.

2. Add /etc/hosts file entries to map the private addresses of the servers to names.

3. Install Unison on each server:

4. Create a profile on each server at /root/.unison/sync_web.prf containing:

Notice the hostname “web2-priv” in red above. The file on web1 should reference web2-priv. The file on web2 should reference web1-priv.

You’ll need to adjust the path listed in the file to match your environment.

5. Next create a script to run Unison with the profile created in the previous step. Name the script /root/ and make it executable.

6. Add an entry to /etc/cronjob to run Unison once per minute:

Everything should now be ready to go. You can test by running the script manually on each server. If there are no errors then try adding, changing and removing files on both servers and verify that the changes are synced within one minute.


Hide NGINX version

For security reasons, if you want to configure nginx to hide it’s version in the server header just add:

server_tokens off;


Perl – Sort associative array by value

Here’s an alpha sort of the values of the associative array named “myarray”:

And here’s the same sort numerically:

And if you want numeric descending:

Of course don’t forget how to sort keys:

And a numerical sort of keys: