How to Open DATABASE_UUID File: Android's .database_uuid (Database UUID) Explained

What is a .database_uuid file?

A .database_uuid file is a hidden marker file created by Android's MediaProvider, the system component that indexes your photos, videos and music. It contains a single UUID (universally unique identifier) that names the phone's current media database. Android's source code describes it as the file "where the current value of DatabaseHelper#getOrCreateUuid is persisted on a physical SD card to help identify stale thumbnail collections."

In plain English: Android keeps small preview images (thumbnails) in folders called .thumbnails. Those previews are only valid for the media database that made them. The .database_uuid file is the label on the box. If the label matches the phone's database, the thumbnails are kept; if it doesn't (say, after a factory reset or after the SD card moved to another phone), Android throws the old thumbnails away and writes a new label.

You only need to open a DATABASE_UUID file if you're curious or worried about it. It isn't a database itself, it isn't related to WhatsApp or any app you installed, and it has no settings or personal data in it. The name just means "the UUID of the database."

How to open a DATABASE_UUID file

Short answer: a .database_uuid is plain text, so any text editor opens it, and the checker above also tells you whether it's valid. You don't need special software to open DATABASE_UUID files:

1. Find it: on the phone or SD card, look in Pictures/.thumbnails, Movies/.thumbnails or Music/.thumbnails. Turn on hidden files first, because names starting with a dot are hidden on Android.
2. Copy it to your computer rather than editing the original on the phone.
3. Read it: drop the copy into the free checker, or open it with Notepad (Windows), TextEdit (Mac) or any text editor. You'll see one line like 3f2b8c1e-9a4d-4e7b-b1c2-6d5e8f9a0b7c.
4. Don't save changes. Leave the file alone, or delete it if you're cleaning up. Android recreates it automatically.

What's inside: the database UUID, byte by byte

A genuine .database_uuid contains exactly 36 characters and nothing else: no line break, no header, no byte-order mark. That makes the file 36 bytes long. Android creates the value with Java's UUID.randomUUID().toString(), which the Java documentation defines as a "type 4 (pseudo randomly generated) UUID," and writes it as UTF-8 text.

When you open a DATABASE_UUID file, the two digits highlighted above are the only fixed parts. RFC 9562, the May 2024 standard that replaced RFC 4122, puts the version number in the 13th hex digit and the variant in the 17th. Everything else is random, so a .database_uuid reveals nothing about you, your phone model or your files. The checker on this page reads both fields and flags anything that isn't a real version 4 UUID.

The same random value also feeds into the version string Android returns to apps from MediaStore.getVersion().

How Android uses .database_uuid to spot stale thumbnails

Android checks every .database_uuid when a storage volume is attached (for example when the phone starts or an SD card is inserted) and again during idle maintenance, a background job that runs while the device is idle and charging. The logic, from the ensureThumbnailsValid() method in MediaProvider, is simple:

This is also why it's fine to open DATABASE_UUID files but not to save them. Two practical consequences follow from that code. First, deleting the file is harmless: a missing .database_uuid is treated as "assume the current thumbnails are fine," and the file is simply rewritten. Second, editing it is not: the comparison is an exact text match, so a line break or space added by a text editor counts as a different UUID and makes Android discard that folder's thumbnails. They regenerate as you browse, so even then nothing is lost but a bit of time.

The UUID changes whenever the media database is created from scratch, for example after a factory reset or after clearing the media storage data. That's exactly when old thumbnails stop matching the media IDs they were saved under, and it's why the file exists.

Where .database_uuid files are found

In the Android Open Source Project code, MediaProvider writes a .database_uuid into three folders on every storage volume it manages, internal storage and SD cards alike, creating the folders if they don't exist:

If you open DATABASE_UUID files from all three folders on one phone, you'll see the same UUID, because MediaProvider keeps a single database for all external storage. Generated thumbnails themselves are always saved to the phone's primary storage, so on an SD card you'll usually find .thumbnails folders that contain only a .database_uuid and a .nomedia file. That is why people notice these folders after inserting a card into an Android phone, or after copying a card's contents to a computer.

The file first appears in MediaProvider for Android 11; the Android 10 version of the same code doesn't contain it. Since Android 11, MediaProvider is a Mainline module that Google can update separately from the rest of the system. If you find a .database_uuid somewhere else, such as DCIM/.thumbnails, keep in mind that phone makers can modify their media software, so the exact folders can vary between brands.

Open DATABASE_UUID files on Windows 11 and 10

Windows shows the .database_uuid file because it doesn't follow Android's "dot means hidden" rule. On Android and other Unix-like systems a name that starts with a dot is hidden; Windows instead uses a separate hidden file attribute, which these files don't have. So when you plug in your phone or an SD card reader, the .thumbnails folder and its contents show up in File Explorer.

1. In File Explorer, open This PC > your phone > Internal shared storage > Pictures > .thumbnails (or the SD card's drive letter).
2. Copy .database_uuid to your Desktop, so you never risk saving changes to the original on the phone.
3. Right-click the copy > Open with > Notepad, or drop it into the checker.
4. Close Notepad without saving. If Windows asks "How do you want to open this file?", that just means no app is set for this extension.

The same steps open DATABASE_UUID files copied from an SD card or a phone backup. If you want Windows to hide these folders again, there's nothing to switch: they aren't marked hidden, so the "Hidden items" option in File Explorer's View menu doesn't affect them. Just ignore them; they're tiny.

Open .database_uuid on Mac and Linux

On a Mac, Finder hides names that start with a dot, so the file may look missing on an SD card. Press Command+Shift+. (period) in Finder to show hidden files, then open the .database_uuid with TextEdit or drag it onto the checker above. On Linux, or in the Mac Terminal, print it directly:

Either way you open DATABASE_UUID files read-only, which is all they need. If wc -c reports 36, the file is untouched. Anything else means it was edited or isn't a real one; the checker shows exactly which characters are extra.

Open DATABASE_UUID files on Android

On the phone itself, file managers hide dot-files by default. To see the file, turn on the "show hidden files" option in your file manager's settings (Files by Google and most other file managers have one), then go to Internal storage > Pictures > .thumbnails. Open it with any text viewer, or copy it to a computer and use the checker.

Whichever app you use to open a DATABASE_UUID file on the phone, avoid editing it there. Some text editors add a line break when saving, which makes Android treat the UUID as different and wipe that folder's thumbnails. If you want it gone, delete it instead.

Can I delete .database_uuid?

Yes. Deleting a .database_uuid never affects your photos, videos or music. When MediaProvider finds the file missing, it assumes its current thumbnails are valid and writes a fresh copy, so the file will reappear the next time the storage is attached or the idle maintenance job runs. Recreating it is the intended behavior, not a sign of malware.

• On an SD card or USB backup you're archiving: delete the .thumbnails folders entirely if you like. They only contain cache data and markers.
• Before deleting: you don't need to open DATABASE_UUID files first; nothing inside is worth saving.
• On a phone you're using: there's no benefit to deleting it. It's 36 bytes, and Android will just put it back.
• Before selling or giving away an SD card: deleting it is fine, though the UUID is random and identifies nothing about you.

Deleting the cached <number>.jpg files in the same folder is also safe. Android builds new thumbnails when an app asks for them, so the only effect is that galleries may load previews a little slower the first time.

Is .database_uuid a virus?

No. A genuine .database_uuid is 36 bytes of plain text containing one random ID. It can't execute, it isn't loaded by any app as code, and it is created by Android's own media system. People worry about it mainly because it's an unfamiliar hidden file that appears without explanation.

To be certain, open the DATABASE_UUID file in the checker and check three things: the size is 36 bytes, the content is a single UUID, and the version digit is 4. If a file named .database_uuid is large, contains readable words or program code, or sits somewhere unusual next to executable files, treat it like any unknown file and scan it with your security software.

The .thumbnails folder: .thumbdata, .jpg and .nomedia files

The .database_uuid file shares its folder with up to three other kinds of files. Here's what each one is and where it comes from:

What's inside a .thumbdata file

On Android 9 and earlier, a component called MiniThumbFile stored small previews in one big file per media type, named .thumbdata + version + - + a hash, for example .thumbdata4--1967290299. The source code reserves a fixed 10,000-byte slot for every media ID: 1 byte flag, an 8-byte check value, a 4-byte length and then the JPEG image. Because every slot is the full 10,000 bytes even when the JPEG is much smaller, and slots exist for every ID up to the highest one, the file grows with the highest media ID: a phone whose IDs reach 20,000 needs about 200 MB, however small the previews are.

The hash in the name is Java's hash of the content address of the media collection, so the tool on this page can tell you which kind of media a .thumbdata file covered (for example, -1967290299 is the images collection) and extract every thumbnail as a normal JPEG. Android 10 removed this format and deletes .thumbdata files from internal storage when it upgrades the media database; copies on old SD cards or backups stay until you remove them.

Unlike the single line of text you see when you open a DATABASE_UUID file, a .thumbdata file holds real images. Thumbnails are reduced copies, not your photos. If you lost the original pictures, though, extracting a .thumbdata file can be the only way to see what they were. Each preview is small, so treat them as a reference, not a replacement.

How to hide or clean up thumbnails

You can't stop Android from creating .thumbnails folders, but you can clear what's in them. Pick the option that matches what you want:

1. Free space on an old phone or card: delete DCIM/.thumbnails (especially large .thumbdata files) with a file manager that shows hidden files. Your camera photos in DCIM/Camera are separate.
2. Fix wrong or blank previews: delete the files inside Pictures/.thumbnails or Movies/.thumbnails. Android generates new ones as you browse.
3. Clean an SD card before archiving it: on a computer, delete the .thumbnails folders inside Pictures, Movies and Music. They will be recreated next time the card is used in an Android phone.
4. Keep thumbnails out of your gallery: nothing to do. Android's scanner places a .nomedia file in these folders so cached previews never appear as photos (see our .nomedia guide).

Don't delete the wrong folder. Remove only folders named exactly .thumbnails. Never delete DCIM, Pictures or Camera themselves.

Common .database_uuid problems and fixes

"How do you want to open this file?" on Windows

No program is registered to open DATABASE_UUID files because they're system files, not documents. Choose Notepad once, or use the checker. Don't tick "Always use this app" unless you open these often.

The file keeps coming back after I delete it

That's by design. MediaProvider recreates the .thumbnails folders and writes the UUID every time it checks the storage. It's harmless and takes almost no space.

Several .database_uuid files contain different UUIDs

If you open DATABASE_UUID files from several folders or devices and the IDs differ, they were written by different media databases: another phone, or the same phone after a reset or after its media data was cleared. Select them together in the checker to compare. On the next check, Android replaces any that don't match and clears that folder's thumbnails.

Thumbnails disappeared after I opened the file in an editor

The editor probably saved it with a line break or byte-order mark, which no longer matches exactly, so Android discarded that folder's thumbnails and rewrote the file. Nothing else was deleted; previews come back as you browse.

Related file extensions

Sources and technical references

.database_uuid is an internal Android convention, not a public file format, so everything on this page was checked against the Android Open Source Project code and the relevant standards.

• MediaProvider.java — Android Open Source Project — defines FILE_DATABASE_UUID = ".database_uuid", ensureThumbnailsValid(), the Pictures/Movies/Music .thumbnails directories and thumbnail pruning.
• DatabaseHelper.java — Android Open Source Project — getOrCreateUuid(): the UUID comes from UUID.randomUUID() and is stored in the user.uuid extended attribute of the database file.
• FileUtils.java — Android Open Source Project — writeString()/readString() (UTF-8, 4,096-byte limit) and the pattern that marks .thumbnails folders as invisible to the scanner.
• MiniThumbFile.java (Android 9) — Android Open Source Project — the .thumbdata layout in DCIM/.thumbnails: 10,000-byte slots with a 13-byte header.
• Modular system components — source.android.com — MediaProvider is a Mainline module since Android 11.
• java.util.UUID — Java SE documentation — randomUUID() returns a type 4 (pseudo randomly generated) UUID.
• RFC 9562: Universally Unique IDentifiers (UUIDs) — UUID string format, version and variant fields.
• Hidden file and hidden directory — Wikipedia — dot-files on Unix-like systems vs. the hidden attribute on Windows.
• How to reveal hidden files in macOS — Macworld — the Command-Shift-period shortcut in Finder.

Frequently asked questions

Summary

• .database_uuid is a 36-byte text file Android's MediaProvider writes in Pictures, Movies and Music .thumbnails folders (Android 11 and later).
• It holds one random version 4 database UUID that tells Android whether cached thumbnails are still valid.
• To open DATABASE_UUID files, use any text editor or the free checker; don't save changes.
• It's not a virus, holds no personal data, and is safe to delete: Android recreates it.