Something is consuming space on my server

Do you have a complete and current backup? If not, I’d shut down, boot from a bootable installer on USB, boot from the recovery partition, or would use another Mac if you have the right combination of hardware for Target Disk Mode with this Mac, and I’d get a complete backup. Disk Utility to an external disk. Sometimes that’s the recovery path, too.

As I mentioned, sometimes the usage display is skewed, and rebuilding Spotlight can sometimes clear that. To poke around at usage with different tools, see below.

https://support.apple.com/en-us/HT201716

If this is a full disk, all sorts of bits of server can start failing, which writes more stuff, which fills more disk, and things get ugly.

So... start by turning off Spotlight. Off. Don’t restart it right now. I’d then reboot through Safe Mode, as that cleans up boot caches and temporary files, and sometimes that’s enough to clear up usage. (Once you’ve gotten some free space, turn Spotlight back on.)

https://support.apple.com/en-us/HT201262

For poking around at usage, df and du are the command line commands to go looking at storage usage. The following two will show the full disk, then a summary of the usage across all directories in the root directory.

df -h /

sudo du -shx /

The man pages will provide a few more details.

If you have add-on anti-malware, add-on anti-virus, add-on cleaners, optimizers, or network-monitoring and security tools, disable those for now (remove them if you can manage it and continue working to resolve this. (Add-on tools have a long history of not doing what they claim or not doing it well, or introducing interesting new and strange behaviors or corruptions, unfortunately.

Use the storage usage setting under the system information under the about this Mac (there’s a very useful display buried under some button like “advanced” or “manage” or some such), or load the Grand Perspective tool and have a look around.

http://grandperspectiv.sourceforge.net/

Lots of potential causes for a server to fill its storage. Misconfiguration, breach, corruption, etc.

Console.app can sometimes point to a culprit, though that display tends to be cryptic and ominous even when everything is working correctly. Look for rapidly repeating blocks, most commonly.

(I’ve seen reports that the storage tab can occasionally misreport, though I’ve not encountered that case. If that happens, a Spotlight rebuild might help.)

I ran into a problem with a 500GB SSD on a server. One of the causes turned out to be TimeMachine and the 'local snaphosts', another was some process dumping large core dumps in /cores.

Local TimeMachine snapshots don't take up much space, unless you thrown something large away and the local TimeMachine spanshots will keep it on disk for 24 hours.