Systems

Linux +10 years
VMware 3 years
Nutanix 2 years
cloud-init 1 year
SaltStack 1 year
Ceph 1 year
bash.sh +10 years
Regex 6 years
Python 2 years
Iptables Firewall 4 years

Databases

OracleDB 8 years
MySQL 5 years
PostgreSQL 5 years

Applications

Apache 10 years
Nginx 5 years
PHP-FPM 5 years
Asterisk 3 years
Tomcat/Jboss 2 years
Postfix 2 years