What would cause a server to "lose" a file, or function?

Hey,

From what you’re describing, it sounds like you’re experiencing a rather peculiar issue. Files and functions “disappearing” or becoming “unrecognized” despite being present and unchanged for months can indeed be baffling. Given the stack you’re working with (CentOS, PHP, Nginx, Apache), there are a few areas we can explore to troubleshoot this issue:

1. OPcache Issues: OPcache improves PHP performance by storing precompiled script bytecode in shared memory, thus eliminating the need for PHP to load and parse scripts on each request. However, if there are issues with the cache, it could lead to PHP not recognizing changes to files or, in rare cases, functions. Clearing the OPcache (opcache_reset();) or temporarily disabling it could help determine if this is the cause. This might also be related to the available RAM on the server.

2. Inodes Running Out: If your server is running out of inodes, it could lead to strange filesystem behavior, including the inability to recognize existing files. You can check inode usage with df -i. Here is a guide on how to check your disk usage as well:

https://www.digitalocean.com/community/questions/28-no-space-left-on-device-error

1. Review Logs: Lastly, don’t forget to go through your Apache, Nginx, and PHP error logs around the times the issues occurred. They might offer more specific clues as to what’s happening. Sometimes, the error messages can be misleading or vague, but they are a good starting point for troubleshooting.

Let me know how it goes!

Best,

Bobby