tesseract "Error opening data file ./tessdata/eng.traineddata" in a Docker container

TL;DR: TESSDATAPREFIX is pointing at a directory that does not exist inside the container, so tesseract falls back to the relative path ./tessdata and finds nothing. Find where eng.traineddata actually lives in the image, set TESSDATAPREFIX to that absolute path, and re-run. One ENV line in the Dockerfile fixes it permanently.

Error opening data file ./tessdata/eng.traineddata

1. Confirm the failure and inspect the variable inside the container: docker exec [container] sh -c 'echo "TESSDATA_PREFIX=$TESSDATA_PREFIX"; tesseract --version' Expected: TESSDATA_PREFIX is empty or a path that does not exist in the image.

2. Find the real traineddata location: docker exec [container] find /usr -name "eng.traineddata" Expected: a path like /usr/share/tesseract-ocr/5/tessdata/eng.traineddata.

3. Test the fix in a throwaway run using the path from step 2: docker exec -e TESSDATA_PREFIX=/usr/share/tesseract-ocr/5/tessdata [container] tesseract scan.png stdout Expected: OCR text prints instead of the data-file error.

4. Make it permanent in the Dockerfile: ENV TESSDATA_PREFIX=/usr/share/tesseract-ocr/5/tessdata then rebuild and re-run. Expected: the error is gone on every run with no manual env flags.

5. If step 2 finds nothing, the language pack is not installed: add tesseract-ocr-eng to the image package install step and rebuild. Expected: eng.traineddata appears under the tessdata directory.

Use this when

• tesseract works on your dev machine but fails in Docker with the data-file error
• the error path starts with ./tessdata
• you built a custom image or switched base images recently

Not for this skill when

• the error names a different language (e.g. fra.traineddata) - that is a missing language pack; install that pack instead
• tesseract is not installed at all in the image (command not found)
• the error happens outside Docker - check the local TESSDATA_PREFIX instead

Variant phrasings

tesseract docker Error opening data file eng.traineddata

tesseract TESSDATA_PREFIX docker not working

tesseract failed loading language eng in container

Why it happens

When TESSDATA_PREFIX is unset or relative, tesseract resolves ./tessdata against the working directory. Local installs usually carry a correct compiled-in default, but Docker images (especially slim or multi-stage builds) often lack the env var or place traineddata somewhere the default does not cover.

Edge cases

• Point TESSDATA_PREFIX at the tessdata directory itself, not its parent; a trailing slash matters on some builds.
• Debian splits the packs: tesseract-ocr alone ships no languages, so install tesseract-ocr-eng (or the pack you need).
• If you mount a custom tessdata volume, the mount must land exactly at TESSDATA_PREFIX.
• The error is about location, not model flavor - tessdatafast vs tessdatabest makes no difference here.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstPiqZwtHlr-V8aRMZ3cJzg