Linux (Red Hat / CentOS)

System administration activities (build, support, manage, patch, break / fix, root cause analysis, troubleshooting, etc.)
Linux Clustering

Solaris

System administration activities (build, support, manage, patch, break / fix, root cause analysis, troubleshooting, etc.)
Solaris Clustering
Solaris virtualization technologies (LDOM / CDOM / Containers)
Oracle RAC
High availability solutions