We highly recommend that you install the latest available, stable version of PostgreSQL 9.x, if it is available to you via your Linux package manager. (There are sufficient advantages to running latest available versions that in many cases, it may be desirable to install PostgreSQL in some way other than via a package manager, if the latter restricts you to an older version. See PostgreSQL Installation - Windows, Mac OS X, Generic Linux for one such option.)

The current major version of PostgreSQL available through many package managers, as of this writing, is 9.6. (See also the PostgreSQL-related recommendations from Nuxeo, the vendor of the content management system used by CollectionSpace.)