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The error fatal: fetch-pack: invalid index-pack output means Git received pack data that it could not turn into a valid index. The message does not name a cause, and it does not by itself mean your repository is corrupt or that a large .git folder is full of junk. A failed transfer can leave temporary files behind, and that can account for disk growth in some cases. Read the lines above the error first, then inspect the pack directory before you delete anything.
What the error reports
During a fetch or clone, Git’s fetch-pack code starts index-pack to consume the incoming pack data and build its index. When the output from that step is not in the form Git expects, the process stops with fetch-pack: invalid index-pack output. The check is on the output of the indexing step, so the message tells you the receiving path failed, not why it failed. The usual candidates are a dropped or truncated connection, local resource pressure during indexing, an invalid pack sent by the server, or a problem specific to the repository.
Read the lines above the error
The fatal line is the last thing Git prints, and it is often the least useful one. GitLab’s Geo synchronization documentation shows the same message appearing alongside consistency (fsck) errors, including one case where an object was flagged for invalid metadata. That means the first actionable error above the fatal line decides the next step. Use this table to triage before running any cleanup.
| First error visible above the fatal line | What it usually points to | Next step |
|---|---|---|
| Connection reset, timeout, or the transfer ending early | Transport interruption | Check for leftover temporary pack files (see below), then retry on a stable network. |
| Out-of-disk-space, out-of-memory, or a process killed by the system | Local resource pressure during indexing | Free disk space, check memory limits, then retry. |
| An fsck or object-validity message, such as an object with invalid metadata | Object-consistency problem | Run git fsck --full and keep the output. Do not prune yet. |
| No earlier line at all, only the fatal message | Not established from the message alone | Save the full output and repeat the operation to see whether it reproduces. |
How a failed fetch can leave a large .git folder
A community technical write-up describes how Git handles incoming packs. Git writes the data to temporary files named tmp_pack_* and renames them to finalized pack files only after the transfer and index creation succeed. If the process is interrupted, those temporary files can stay in .git/objects/pack. According to that write-up, Git does not treat them as packs, and git count-objects -vH reports them in the garbage and size-garbage fields. The author puts it this way: “Git will never treat that file as a pack.”
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This explains how a failed transfer can leave disk space in use. It does not show that every oversized .git folder is mostly leftover files. The 6 GB figure comes from one reported case, and the write-up does not establish the complete state of that machine’s filesystem. Treat the mechanism as a hypothesis to test in your own repository.
Diagnose before you delete
- Save the complete output of the failed command, including every line above
invalid index-pack output. Redirect a repeat run to a file if you need to:git clone --verbose <url> 2>&1 | tee clone.log. - Confirm that no Git process is using the repository. On Linux, run
pgrep -a git. Do not remove or prune anything while a fetch, clone, or gc process is still running against that repository. - Measure the folder and the pack directory:
du -sh .gitanddu -sh .git/objects/pack. Then list temporary files withls -lh .git/objects/pack | grep tmp_. - Run
git count-objects -vHin the repository. Compare thesize-garbagevalue with the total size. Ifsize-garbageis a small fraction of the directory, leftover temporary files are not the main cause of the growth, and you should look elsewhere, such as large packs or a repository that really holds a lot of history. - Run
git fsck --full. Read its output carefully. Reports about unreachable or dangling objects are different from reports about missing or broken objects. Only the second kind suggests real damage.
When pruning is safe, and when it is not
Git’s normal cleanup keeps unreachable objects for a grace period, which by default is about two weeks. Pruning with an immediate expiry removes that safety window. The commands are git prune --expire=now and git gc --prune=now. Run them only when all of the following are true:
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- No Git process is active on the repository.
- The
git fsck --fulloutput shows garbage or dangling objects and no missing or broken objects that matter to you. - You have a backup copy of the repository, or you can reclone it from the remote if something turns out to be needed.
If the fsck output reports missing or broken objects, do not improvise. Make a copy of the repository directory, then reclone from the remote into a fresh directory. Deleting files by hand from .git/objects/pack is the riskiest option, because it skips the checks that Git’s own prune performs.
Preventing the error from recurring
- Check free space before a large fetch. A transfer that needs more room than is available is one of the most common ways to produce an interrupted pack.
- Remove a partial clone before retrying. If a clone failed, delete the incomplete directory and start again rather than running a second clone into the same folder.
- Use a shallow clone when you only need recent history.
git clone --depth 1 <url>transfers less history. A guide to large repositories cautions that a shallow checkout can still be large and can still run into resource or network limits, so this helps only when the history itself is the problem. To get the full history later, rungit fetch --unshallowinside the repository. - Re-measure after a failure. Run
git count-objects -vHafter any interrupted fetch so you can see whether garbage is accumulating.
What is and is not established
The error message identifies a failure in Git’s fetch and index handling, and Git’s source supports the explanation above. GitLab’s documentation shows that the same message can appear in an object-consistency context. The temporary-pack mechanism comes from a single community write-up, which is not an official diagnosis. No independent study or statistic about this particular error is available, and the 6 GB figure should not be read as a threshold. For your own repository, the measurements in the diagnostic steps are the only reliable way to decide whether leftover files explain the size.
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In practice, a clean git fsck --full, a size-garbage value that accounts for most of the growth, and no active Git process are the conditions under which pruning the leftovers is a reasonable step. Anything else calls for preserving the logs and recloning.
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