First you will need to add the Linux Server as a MediaAgent into the CommServe.
Then you will need to configure a Disk Library, selecting the Mount Location on the Linux MediaAgent.
Depending on whether it is Local Volume or NFS mounted on the Linux Server, follow the following Documentation - http://documentation.commvault.com/commvault/v11/article?p=9299.htm
Once the above is done, configure your Secondary Copy pointing to this Linux MA
Hopefully that helps