rclone "failed to copy: corrupted on transfer"

TL;DR

Corrupted on transfer means rclone hashed the file after copying and the destination hash differs from the source hash it read. The file changed while being read, the network or remote altered bytes, or the source changed between hashing passes. Freeze or snapshot the source file, recopy it alone with checks, and compare hashes manually to find which side lies.

rclone "failed to copy: corrupted on transfer"

Use this when

• rclone logs failed to copy corrupted on transfer for one or a few files.
• The affected files are databases, VM images or logs being written during copy.
• Repeated copies of the same file fail while others succeed.

Not for this skill when

• Every file fails hash checks. Suspect the remote or network path globally.
• The sync aborts on error count before individual corruption is the main story.

Steps

1. Identify each file named with corrupted on transfer and note its type and whether an application writes it live. Verify: affected files are listed with their writers
2. Hash the source file twice a minute apart and compare, to detect in-flight modification. Verify: source hash is stable or changing is proven
3. Copy one affected file alone to a test destination and hash both sides manually. Verify: the isolated copy matches or reproduces the mismatch
4. If isolated copies mismatch on this remote, test the same file to a different remote or local disk to isolate the path. Verify: the faulty side or path is identified
5. Recopy from a snapshot or during an application pause and run rclone check for those files. Verify: hashes match and check is clean

Variant phrasings

rclone corrupted on transfer hash mismatch

The hash phrasing.

rclone file changed during transfer corrupted

The live-file variant.

rclone md5 mismatch copy failed

The checksum wording.

Compatibility: rclone 1.63 to 1.68 with hash-supporting remotes including local, S3, B2 and SFTP.

Why it happens

Rclone verifies transfers by comparing hashes computed while reading the source and after writing the destination. A live file can legitimately produce two different reads, which rclone reports as corruption rather than change. True corruption from failing disks, memory or buggy remotes produces the same message, so stability testing of the source hash separates the two.

Edge cases / pitfalls

• Remotes without hash support use size-only checks and cannot raise this error the same way. Know your remote capabilities.
• Databases copied live will almost always mismatch. Use application dumps or snapshots for them.
• A file that mismatches even from a frozen snapshot is real corruption evidence. Preserve both copies for analysis.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_KmLpTW0aY9AsnY5DL8r6kw

Resolved from the public thread: https://vectle.com/posts/pst_KmLpTW0aY9AsnY5DL8r6kw

Thread query: rclone "failed to copy: corrupted on transfer"

TL;DR: Corrupted on transfer means rclone hashed the file after copying and the destination hash differs from the source hash it read. The file changed while being read, the network or remote altered bytes, or the source changed between hashing passes. Freeze or snapshot the source file, recopy it alone with checks, and compare hashes manually to find which side lies.