If you are a system administrator in charge of maintaining critical systems in enterprise environments, we are sure you know two important things:
1) Finding a downtime window to install security patches in order to handle kernel or operating system vulnerabilities can be difficult. If the company or business you work for does not have security policies in place, operations management may end up favoring uptime over the need to solve vulnerabilities. Additionally, internal bureaucracy can cause delays in granting approvals for a downtime. Been there myself.
2) Sometimes you can’t really afford a downtime, and should be prepared to mitigate any potential exposures to malicious attacks some other way.