Description of problem:
In the upcoming release of Ceph Infernalis (v9.1.0 upstream version)[1].  The default user name and group name will be "ceph".  This could cause problems when upgrading the packages from a previous Ceph release, if the "ceph" user already exists.

Section 2.9 is sub-titled correctly in the Ceph Installation Guide[2], but an updated needs to be made to reflect this potential problem, by asking the end-user to remove the "ceph" user before they perform an upgrade.  An upstream tracker issue[3] has also been created to fix the upstream documentation.

Version-Release number of selected component (if applicable):
Ceph 1.3.1 Installation Guide

Additional info:

[1] - http://docs.ceph.com/docs/master/release-notes/#v9-1-0-infernalis-release-candidate
[2] - https://access.redhat.com/documentation/en/red-hat-ceph-storage/version-1.3/red-hat-ceph-storage-13-installation-guide-for-rhel-x86-64/chapter-2-pre-installation/
[3] - http://tracker.ceph.com/issues/13502