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The files macOS does not show you

18 August 20269 min read

Press Command-Shift-Period in Finder and roughly forty things appear that were not there a second ago. Most are harmless. Two of them are why your external drive is still full after you emptied it.

macOS hides files for a reason that has nothing to do with secrecy. It hides them because a folder containing eleven documents and forty pieces of bookkeeping is a worse folder than one containing eleven documents.

The trouble starts when you are trying to work out where your disk went, because some of that bookkeeping is enormous, and none of it appears in a normal Finder window.

Three separate ways a file gets hidden

These are genuinely different mechanisms with different rules, and knowing which one you are looking at tells you something useful about the file.

1. The leading dot

Any file whose name starts with . is hidden. This is inherited from Unix, where it was reportedly an accident: someone writing the code to skip the special entries . and .. wrote a check that also skipped everything else beginning with a dot, and the behaviour became a convention because it turned out to be useful.

Almost every configuration file on your Mac is hidden this way. Reveal them with Command-Shift-Period.

2. The hidden flag

A file can have a normal name and still be hidden, because macOS stores a flag on it. /usr, /bin and /private are hidden this way. You can see the flag with:

ls -lO /

Anything showing hidden in the flags column is using this mechanism rather than a dot. Command-Shift-Period reveals these too.

3. Hidden by Finder specifically

The Library folder in your home directory is the important one here. It is not dot-prefixed and does not carry the hidden flag. Finder simply refuses to display it, which is why Command-Shift-Period does not bring it back.

To reach it, hold Option while clicking Finder's Go menu, and Library appears in the list. Or press Command-Shift-G and type ~/Library.

This distinction matters because Library is where nearly all of your reclaimable space lives, as covered in the article on app leftovers. The single most useful hidden folder on the Mac is hidden by the one mechanism the standard shortcut does not touch.

The catalogue

What you will actually see when you turn hidden files on, roughly in order of how often you will encounter it.

The hidden things that are actually using your disk

Most of the catalogue above is kilobytes. Four entries are not, and these are the ones worth looking for.

.Trashes on external drives

This is the one that produces genuine confusion. Every volume gets its own trash folder, named .Trashes, at the root of that volume. When you delete a file from an external drive, it is moved there. It stays on that drive, still occupying space, until the Trash is emptied while the drive is connected.

So: you delete 40 GB from a backup drive. You eject it. Later you empty the Trash. The 40 GB is still on the external drive, because macOS could not reach it. The drive stays full and nothing in Finder explains why.

The fix is to reconnect the drive and empty the Trash with it mounted. To see what is sitting there:

du -sh /Volumes/*/.Trashes 2>/dev/null

Package manager caches

If you write software, .npm, .cargo, .gradle, .m2 and .pub-cache are all download caches that grow without limit and are never pruned by anything. Several gigabytes each is normal. Everything in them can be re-downloaded, so deleting them costs you time on the next build and nothing else.

.Spotlight-V100

The search index. On a large volume it can be several gigabytes. It is not junk and deleting it means Spotlight reindexes the whole drive, which takes hours and hammers the disk. Only worth touching if search is genuinely broken, and even then there are better ways to ask for a rebuild.

Old .fseventsd logs

Rarely large on a healthy system, occasionally enormous on a drive that has had millions of file changes. Worth looking at only if a disk map points you there, which is the honest answer for most of this category.

The ._ files on USB sticks

A category of its own, because it only appears on drives formatted for something other than a Mac, and it baffles everyone the first time.

macOS attaches extra information to files that most filesystems have no way to store: Finder tags, custom icons, the quarantine flag that produces the "downloaded from the internet" warning, and where a file came from. On an APFS or HFS+ drive this rides along invisibly as extended attributes.

Copy that file to a FAT32 or exFAT USB stick, which has no such concept, and macOS refuses to lose the information. It writes a second hidden file alongside the first, with the same name and a ._ prefix, containing everything that would not fit. Copy report.pdf and the stick receives both report.pdf and ._report.pdf.

They are individually tiny and collectively noticeable if you have copied tens of thousands of files. Their real cost is social: anyone opening that drive on Windows sees a duplicate of every file you gave them, and reasonably concludes something went wrong.

You can strip them from a drive before handing it over:

dot_clean /Volumes/YourDriveName

That merges the extra data back where possible and removes the separate files. Nothing of yours is lost, because the information they carry is metadata about the file rather than the file's contents. The same command is the fix for a drive that has accumulated them over years of use.

Should you leave hidden files visible?

Probably not, and this is a mild opinion rather than a rule.

Leaving them on permanently means every folder you open has a .DS_Store in it, your home folder acquires a dozen configuration files you will never edit, and the signal to noise ratio of every Finder window drops for no ongoing benefit. The files were hidden because they are not things you act on.

The shortcut is one keystroke. Turn them on when you are looking for something, turn them off when you are done. The exception is if you write software, in which case you are editing dot-files often enough that leaving them visible saves real time.

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