Automatically monitor error logs and send email for fatal errors

I use a variety of monitors to check for website uptime and server uptime e.g. uptime robot, monitis etc. These work great if e.g. server down or website 500 server error - or other network related issues where the server or site response is not pingable. However, if a single website experiences a Fatal Error - for example, an automated software upgrade happens (e.g. a wordpress update) which then introduces a fatal error in the website code (e.g due to a plugin code conflict or similar) - leading to the White Screen of Death (WSOD) on the website, then none of these monitors will alert me - because technically, the site is still up and pingable. But of course, the site is not "up" on the front end and invariably, this will usually lead to a call or email from a client asking "why is my website offline?" So - looking for suggestions please. What service / services exist for Apache or Linux - either via cPanel or other - that can monitor / scan e.g. the error_log for the various websites on the server and alert me if a fatal error shows up? I have found this Wordpress plugin, but I really want to do this at the server level, not at individual level: wordpress.org/plugins/error-log-monitor/ I would love to install something at the server admin level - rather than at each individual website - however, I don't think website fatal errors show up in apache/logs/error_log - but they do of course, in the individual site error_log. The closest I can find is a cron script - does anyone have any experience or luck with it? looklinux.com/cron-script-to-monitor-php-error-fatal-warning-and-notice-on-email/ I also found this one: octopussy.pm/ What about Nagios? Would that be able to achieve the above? Thanks in advance for your suggestions.