Symptoms include the following on connect:
ERROR:ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux Error: 2: No such file or directory
You will also see some errors on your tnslisteners.log.
Oracle XE on Fedora X86_64
If you encounter problems installing Oracle XE on Fedora x86_64, install the ‘libaio.i686’ package before installing oracle-xe. If you have already installed the oracle-xe package, you may have to remove it and then reinstall it to ensure that it initializes the database correctly (it will have failed the first time).