I tied to update to the latest Calibre (2.0.0) and discovered it will not run on CentOS 6. It appear to need glibc 3.4.15 and Qt 5. CentOS 6 uses glibc 2.12 and Qt 4. That can probably be be fixed with some static linking but getting two version of glibc to work together is tricky. If, like me, you inadvertently installed it, you can download an earlier version here:
The following will extract the 1.48.0 version which is the next to latest:
$ sudo rm -rf /opt/calibre/* && sudo tar -xvjf calibre-1.48.0-x86_64.tar.bz2 -C /opt/calibre
You may need to make the following symbolic link.
/usr/bin/calibre -> /opt/calibre/calibre