install Galera but mariadb existing on system I try to install galera on ubuntu 14.04 system. It has already got mariadb and it's working. How can I install it? 

my command :

sudo apt-get install -y rsync galera-3 mariadb-galera-server


it gives error

Reading package lists... Done
Building dependency tree       
Reading state information... Done
rsync is already the newest version.
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 mariadb-galera-server : Depends: mariadb-galera-server-5.5 (= 5.5.46+maria-1~trusty) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
Try using aptitude instead of apt-get. It is more intelligent. It not only will handle downgrading conflicting packages for you, but will make a series of recommendations asking you which of many possible suggested working scenarios you would like. e.g.

sudo aptitude install rsync galera-3 mariadb-galera-server


If you don't have aptitude on your machine yet, get it with

sudo apt-get install aptitude