Mojave is eating storage like candy, no matter how much I free up By my count, I should have 40-50gb free. But starting a few weeks ago, I'd wake up having created no new files, and 5gb would be gone, or 10gb.

Today, it told me that no storage was left. I freed up 5gb by deleting some apps I no longer used... and it has slowly eaten that as I watch the finder window's footer. Down to 546mb at the moment. And there's nothing else left to get rid of.

What the hell is going on? I have a Terminal.app open. I have a Firefox window open (that I'm typing into right now). And a few Sublime tabs.

If I reboot, I'll get maybe 11-12gb of this back... and it will slowly gobble that up over a period of at most a few hours. I don't know what's going.

I don't think this is malware, no files are messed up anywhere, no ransomware horseshit. Where do I start checking? Down to 373mb now. 

It has done this in the past, of course, but an hour later whatever it was using that storage for would be freed, and I'd have no incidents for weeks/months afterward. This is the first time that it didn't self-correct.
You might want to check the disk usage with something like 

du -h 

which will scan the current working directory.

or 

du -hs if you have an idea which directory might be taking much of the space.

OmniDiskSweeper is also an awesome free tool to see where all the files are taking so much space but be extra careful with it as you would not want to remove any system files, here is a video where you may get some ideas.

Another reason can be swap memory. When there is a lot of applications running and the system memory cannot take it anymore, it saves temporary memory into ssd, as a result when you are rebooting, it is going away but then the system is making it again. You can check your memory usage by:

vm_stat | perl -ne '/page size of (\d+)/ and $size=$1; /Pages\s+([^:]+)[^\d]+(\d+)/ and printf("%-16s % 16.2f Mi\n", "$1:", $2 * $size / 1048576);'


Or by:

sysctl vm.swapusage
&gt; vm.swapusage: total = 5120.00M  used = 4237.00M  free = 883.00M  (encrypted)


For more info: Is there a Mac OS X Terminal version of the &quot;free&quot; command in Linux systems?