When you have a 120gb SSD you keep an eye on such things. Still 85gb+ free, but watching that slowly get eaten away buy who knows what. I'm not downloading anything that I leave on the drive with the exception of the occasional jpg. Usually motorcycles or drums... No games or movies or anything of the "larger" variety.

What gives!?!?!

Linux Mint 18 here.

On console:
du
df

df displayed a lot of cache files in directories I can't see using the GUI. ./.cache/google-chrome/

How can I get rid of these files if they're just cached versions of stuff I don't even need?

$ du -h --max-depth=1 /home/

$ du -h --max-depth=1 /tmp/

$ du -h --max-depth=1 /var/log/

for debian based distros

$ du -h /var/cache/apt/archives/

When you update via the CLI, the downloaded packages that get installed don't always go away. Once they're installed you can safely rm those files IMO. But mostly I archive the install to a large disk and do a fresh install to reclaim space. Part paranoia, part keeping my install skills fresh. Not much worse than going somewhere on a fresh install and realizing that you didn't install the wireless networking tools.

For Debian distros, it is always safe to remove downloads of packages (after installation).
Run as root,

Probably you can remove it, but chrome can be configured to put it into another dir and I think also the (max) size can be specified.

The snapshotting that btrfs does will slowly use up disk space. You can clean out your browser cache all you want but the snapshots will still be there. And they hang around for a while.

You can remove it, but you need cto clear all your browser cache

Lots of random writes aren't good for SSD's.

Try the lsof ("list open files") command.

My guess is that you probably have some kind of daemon that is continuously writing to some file, without ever closing it. Thus, the file's directory-entry is never being updated, and so it is not readily apparent where the disk space is going.

(Incidentally, this issue is common to most operating systems ...)

The odds are also reasonable that this behavior, while as-yet unexplained to you, is probably benign.

You can also use a chroot jail to whitelist or blacklist any program. Though nothing stops a process from editing it own memory and escaping from the jail.

yeah to what they said, and as well, every time you update. Them updates can get a little bit bigger because of the added code in the file, which may only take a few kb but as you see it does add up over time. repeating others, tmp files, logs and such too is something to look at.

check the log files.

cd /var

check if any log files is consuming your space

On modern SSDs this is less of an issue than it used to be in the past.

SSD? do you trim your drive at least once a week?