Q. Where is the RPM database located under Fedora Core Linux? I need to backup the same so that it can be used for restore purpose. May be I can use the same for troubleshooting purpose.
A. /var/lib/rpm directory stores all files used by rpm command. To be frank you don't have to backup /var/lib/rpm directory. You can use rpm command to get list of packages and restore them later on.
If you get rpm database corruption error, try to follow instructions mentioned here to fix database problem with following two commands:
# rpm --rebuilddb
# rpmdb_verify Packages
Above command will rebuild the RPM database for Fedora Core and recreate the necessary files for you.
Please note that above command works with Red Hat Linux, Fedora Core and Cent OS.