Linux OS
Configuration files for different services (ntp, dns, disk subsystem, kernel params, security)

Performance debugging (cpu, io, network)

Unix Shell scripting
Creating scripts for monitoring managed applications/automating tasks;

Debugging scripts;

Oracle Database
Install/upgrade Oracle RDBMS including Clusterware, ASM, RAC on linux environment

User security

RMAN backup & recovery

Dataguard configuration

Space management

Performance tuning

PostgreSql Database
Install/upgrade on linux environment

User security

backup & recovery

Standby configuration

Space management

Performance tuning

Microsoft SqlServer database
Install/upgrade on windows environment

User security

backup & recovery

Standby configuration (Log Shipping / Availability Groups)

Space management

Performance tuning