Corrupted World on Your Minecraft Server: How to Recover It

How to tell it's a corrupted chunk

The world is saved in chunks, 16 × 16 block pieces, and chunks are grouped 32 by 32 into region files (.mca). When the server can't read a chunk, it usually generates it again from the seed: that's why what you see is a square of untouched terrain with straight edges, right where something of yours used to be.

The other signs: the server freezes or shuts down when someone gets near a specific spot, or the “Console” shows errors mentioning a chunk or a region file with some coordinates (for example, “Couldn't load chunk [62, -19]”). Those are chunk coordinates, not block ones: multiplied by 16 they give the position in blocks.

If what won't start is the whole server, the problem may be something else (Java, a plugin, the version): paste the log into the log analyzer or see why it won't start.

Why a world gets corrupted

The most common cause is the server shutting down abruptly while it's saving: a power cut if you run it at home, closing the console window or forcing it off instead of waiting for it to stop on its own.

The second, a full disk: if there's no space left when the server saves, the file is left half-written. It happens most to people who pregenerate a lot of map on a small disk.

And the rest: opening the world with an older version than the one that saved it (you can't downgrade on the same world: what to do), removing a mod that added blocks, and editing the world with a program that isn't up to date with your version.

Before you touch anything

1. Stop the server

   With “Stop” in the panel, and wait until it says “Offline”: if it's still running, it may write over the chunk again while you fix it.

2. Save the world as it is

   Even broken: if the fix goes wrong, you come back to this point. On a plan, “Backups” → create a backup. On the free server, which has no backups, in “Files” tick the world folder (usually world), “Compress” and download the file that appears.

3. Note where the damage is

   The coordinates from the error in the “Console” or, if you've seen it in game, those on the F3 screen (in blocks) of a spot in the broken area.

Which file needs fixing

Each region file covers 512 × 512 blocks and is called r.X.Z.mca. To find yours, divide the block coordinates by 512 and keep the whole number below (rounding negatives down too): at x = 1000, z = -300 you get r.1.-1.mca. If you have chunk coordinates, divide by 32.

Since 26.1 (what we ship on NapNodes), they're in world/dimensions/minecraft/overworld/region for the surface, with the_nether and the_end instead of overworld for the other dimensions. In earlier versions, in world/region, world_nether/DIM-1/region and world_the_end/DIM1/region (how the folders changed).

Next to region are the entities folder (animals, armor stands, item frames…) and the poi folder (beds, villager workstations), with files named the same way. If what's missing is your animals, or villagers can't find their workstation, the damaged file is there.

If you have a backup

The quickest way is to restore it whole: in the panel, “Backups” → the backup → restore. The server goes back to the moment it was made, losing everything that happened since, across the whole world. NapNodes plans make an automatic daily backup every night, so at most you lose a day (how backups work).

If you've played a lot in the rest of the world since then, it's better to swap only the damaged file: download the backup, open it on your PC (it's a compressed file), find the r.X.Z.mca for that area and, with the server stopped, upload it in “Files” to its folder, over the broken one. Only that 512 × 512 area goes back to the backup's day; everything else stays as it was.

If you don't have a backup

You can delete just the damaged part so the server generates it again from the seed. Whatever was built in those chunks is lost, but the rest of the world is fine and the server stops crashing.

1. Download the region folder

   With the server stopped, in “Files” compress the region folder of the right dimension and download it. If it's very big, the r.X.Z.mca file for the area is enough.

2. Open it with MCA Selector

   It's a free, open-source program that shows the map from above, chunk by chunk. Use the latest version and check that it says it supports your world's: an old one can damage it further.

3. Delete the broken chunks

   Go to the coordinates you noted, select the damaged chunks (they usually look empty or odd) and delete them. If you can't see them, you can delete the whole region file, but then all 512 × 512 blocks are regenerated.

4. Upload it and start

   In “Files”, upload the fixed file over the old one, “Start” and go to the area: fresh terrain should generate with no errors in the “Console”.

If the broken one is level.dat

level.dat holds what belongs to the whole world: the seed, the time, where you spawn. If it's damaged, the server won't load the world or creates a new one as if it didn't exist. In the same folder there's usually a level.dat_old, the version from the previous save.

With the server stopped, in “Files” rename level.dat to level.dat_broken and level.dat_old to level.dat, and start it. At most you lose what changed in that last save; builds live in the region files and aren't touched.

Keep it from happening again

Always stop with “Stop” or with stop in the “Console”, and wait for it to finish: that way the server saves everything before closing. Don't force it unless it has frozen.

Watch the disk. On the NapNodes free server the disk is small and you get an email at 80 % and at 95 %: if you get one, delete worlds or backups you don't use before pregenerating more.

Make a backup before anything big: updating the version, installing or removing mods, changing the server type. And don't open the world with a version older than the one it has.

And what gives the most peace of mind: backups that happen by themselves. NapNodes plans keep one every night on top of yours; the free server has none, so there the backup is the one you download yourself (from free to a plan).

Frequently asked questions