[INS-30131]Initial setup required for the execution of installer validations failed. Encountering this error in Fedora 20
To see the real reason of this error in console output, use:

./runInstaller -debug -logLevel finest


In my case the reason was no execute permission for the file:
    '/tmp/CVU_12.1.0.2.0_oracle/exectask.sh'

So you simply need to add execute permission to all scripts and executable files in this directory, without exiting the installer.
Open the second console and use:

cd /tmp/CVU_12.1.0.2.0_oracle
chmod +x *.sh
chmod +x exectask
chmod +x cvuhelper


Then resume installation. It should install without further problems!

P.S.

Important remark about starting the database. It is not sufficient to use:

dbstart $ORACLE_HOME


and / or

lsnrctl start


You need to log in to the idle instance:

sqlplus SYS AS SYSDBA


and then use sqlplus command:

startup;


Then you can connect SYS@ORCL AS SYSDBA without error ORA-12514, assuming that you have set environment variable ORACLE_SID=orcl

Read also Oracle 12c Post Installation Mandatory Steps.