sqlplus (Oracle XE) doesn't start on CentOS 7
This version of Oracle XE is based on 11g2 edition, which is not compatible with CentOS 7.

In fact, it isn't even 100% compatible with CentOS 6, however it will run there without problems, after you install a number of RPM packages not installed/required by Oracle installer (especially libaio both 32/64-bit).

These are formal OS requirements for XE 11g2:


Oracle Linux, Red Hat Enterprise Linux, or CentOS - versions 4.7+ or 5.2+
SUSE Linux Enterprise Server - versions 10 SP2 or 11