Abort incomplete multipart uploads

A multipart upload (MPU) is an S3-compatible operation that uploads a large object in independent parts. If the client crashes, loses its connection, or otherwise stops before calling CompleteMultipartUpload or AbortMultipartUpload, the uploaded parts remain in the bucket as an incomplete multipart upload. Incomplete multipart uploads consume storage, do not appear in normal object listings, and prevent the bucket from being deleted. Use this page when you need to:

Free storage occupied by abandoned upload parts.
Unblock a DeleteBucket call that fails with BucketNotEmpty.
Reset upload state for a client that is stuck or misbehaving.

To prevent incomplete multipart uploads from accumulating in the first place, configure an AbortIncompleteMultipartUpload lifecycle rule. The procedures on this page handle uploads that already exist; the lifecycle rule prevents them from coming back.

Prerequisites

Before you start, make sure you have:

An Access Key for the organization that owns the bucket.
A configured S3-compatible client (AWS CLI, s3cmd, or Boto3).
Permission to call s3:ListBucketMultipartUploads and s3:AbortMultipartUpload on the bucket.

List incomplete multipart uploads

List the incomplete multipart uploads in a bucket. Each upload has a unique UploadId and is identified by the object key it was targeting.

AWS CLI
s3cmd
Boto3

Replace [BUCKET-NAME] with the name of your bucket.

List incomplete multipart uploads with AWS CLI

aws s3api list-multipart-uploads --bucket [BUCKET-NAME]

The response includes an Uploads array. Each entry has a Key (the object key the upload targets), an UploadId, and an Initiated timestamp.

Example output

{
    "Uploads": [
        {
            "Key": "datasets/large-archive.tar",
            "UploadId": "2~JZ8QkN9R-EXAMPLE-UPLOAD-ID",
            "Initiated": "2026-04-15T20:14:03.000Z"
        }
    ]
}

If the bucket has no incomplete multipart uploads, the response is empty.

Replace [BUCKET-NAME] with the name of your bucket.

List incomplete multipart uploads with s3cmd

s3cmd multipart s3://[BUCKET-NAME]

The output lists each in-progress upload with its initiation timestamp, target key, and upload ID.

Set environment variables for your CoreWeave credentials:
```
export ACCESS_KEY_ID="[ACCESS-KEY-ID]"
export SECRET_ACCESS_KEY="[SECRET-ACCESS-KEY]"
```
Alternatively, configure your CoreWeave credentials to work with the AWS CLI. We recommend using a separate profile for CoreWeave AI Object Storage to avoid conflicts with your other AWS profiles and S3-compatible services. If you don’t set up this configuration, you might encounter errors when using AI Object Storage.
Configure CoreWeave credentials
1. Create a new credentials file and profile in your CoreWeave configuration directory.
  Create a new credentials file and profile
  AWS_SHARED_CREDENTIALS_FILE=~/.coreweave/cw.credentials aws configure --profile cw
2. When prompted, provide the following values:
  - AWS Access Key ID: The Access Key ID of your CoreWeave AI Object Storage Access Key.
  - AWS Secret Access Key: The Secret Key of your CoreWeave AI Object Storage Access Key.
  - Default region name (Optional): To set a default region, see CoreWeave Availability Zones.
  - Default output format: Use json for JSON output.
3. Set the default endpoint URL to the appropriate endpoint for your use case:
  - The primary endpoint, https://cwobject.com, for use outside a CoreWeave cluster.
  - The LOTA endpoint, http://cwlota.com, for use inside a CoreWeave cluster. The LOTA endpoint routes to the LOTA path for best performance.
  Set the primary endpoint for local development
  AWS_CONFIG_FILE=~/.coreweave/cw.config aws configure set endpoint_url https://cwobject.com --profile cw
4. Set the S3 addressing_style to virtual:
  Set virtual addressing style
  AWS_CONFIG_FILE=~/.coreweave/cw.config aws configure set s3.addressing_style virtual --profile cw

Replace [BUCKET-NAME] with the name of your bucket.

List incomplete multipart uploads with Boto3

import os
import boto3
from botocore.client import Config

boto_config = Config(
    region_name='US-EAST-04A',
    s3={'addressing_style': 'virtual'}
)

s3 = boto3.client(
    's3',
    endpoint_url='https://cwobject.com',
    aws_access_key_id=os.environ['ACCESS_KEY_ID'],
    aws_secret_access_key=os.environ['SECRET_ACCESS_KEY'],
    config=boto_config
)

paginator = s3.get_paginator('list_multipart_uploads')
for page in paginator.paginate(Bucket='[BUCKET-NAME]'):
    for upload in page.get('Uploads', []):
        print(f"{upload['Initiated']}  {upload['UploadId']}  {upload['Key']}")

A single call returns up to 1000 uploads. To enumerate every incomplete upload in a bucket, paginate using KeyMarker and UploadIdMarker from the response (or use the Boto3 paginator shown above).

Abort a specific multipart upload

Abort one incomplete multipart upload by its UploadId. All parts already uploaded for that ID are permanently removed.

AWS CLI
s3cmd
Boto3

Replace [BUCKET-NAME] with your bucket name, [OBJECT-KEY] with the upload’s target key, and [UPLOAD-ID] with the UploadId from the listing.

Abort a multipart upload with AWS CLI

aws s3api abort-multipart-upload \
    --bucket [BUCKET-NAME] \
    --key [OBJECT-KEY] \
    --upload-id [UPLOAD-ID]

A successful call returns no output.

s3cmd identifies an upload by its UploadId and target object URI. Replace [BUCKET-NAME], [OBJECT-KEY], and [UPLOAD-ID] with values from the listing.

Abort a multipart upload with s3cmd

s3cmd abortmp s3://[BUCKET-NAME]/[OBJECT-KEY] [UPLOAD-ID]

Abort a multipart upload with Boto3

import os
import boto3
from botocore.client import Config

boto_config = Config(
    region_name='US-EAST-04A',
    s3={'addressing_style': 'virtual'}
)

s3 = boto3.client(
    's3',
    endpoint_url='https://cwobject.com',
    aws_access_key_id=os.environ['ACCESS_KEY_ID'],
    aws_secret_access_key=os.environ['SECRET_ACCESS_KEY'],
    config=boto_config
)

s3.abort_multipart_upload(
    Bucket='[BUCKET-NAME]',
    Key='[OBJECT-KEY]',
    UploadId='[UPLOAD-ID]'
)

Abort every incomplete multipart upload in a bucket

To clear every incomplete multipart upload at once, list them and abort each one in a loop. Use this when you are preparing a bucket for deletion or recovering from a large-scale client failure.

AWS CLI
s3cmd
Boto3

This shell loop pages through list-multipart-uploads and aborts every upload it finds. Replace [BUCKET-NAME] with the name of your bucket.

Abort all incomplete multipart uploads with AWS CLI

BUCKET="[BUCKET-NAME]"

aws s3api list-multipart-uploads --bucket "$BUCKET" \
    --query 'Uploads[].[Key, UploadId]' \
    --output text \
| while read -r KEY UPLOAD_ID; do
    [ -z "$KEY" ] && continue
    aws s3api abort-multipart-upload \
        --bucket "$BUCKET" \
        --key "$KEY" \
        --upload-id "$UPLOAD_ID"
  done

If the bucket has more than 1000 incomplete multipart uploads, run the loop again until list-multipart-uploads returns an empty response.

This script paginates through every incomplete multipart upload in the bucket and aborts each one.

Abort all incomplete multipart uploads with Boto3

import os
import boto3
from botocore.client import Config

BUCKET = '[BUCKET-NAME]'

boto_config = Config(
    region_name='US-EAST-04A',
    s3={'addressing_style': 'virtual'}
)

s3 = boto3.client(
    's3',
    endpoint_url='https://cwobject.com',
    aws_access_key_id=os.environ['ACCESS_KEY_ID'],
    aws_secret_access_key=os.environ['SECRET_ACCESS_KEY'],
    config=boto_config
)

aborted = 0
paginator = s3.get_paginator('list_multipart_uploads')
for page in paginator.paginate(Bucket=BUCKET):
    for upload in page.get('Uploads', []):
        s3.abort_multipart_upload(
            Bucket=BUCKET,
            Key=upload['Key'],
            UploadId=upload['UploadId'],
        )
        aborted += 1

print(f"Aborted {aborted} incomplete multipart uploads in {BUCKET}.")

Verify the bucket is clear

After aborting, re-run the List incomplete multipart uploads procedure. The response should be empty. If you were preparing the bucket for deletion, return to Empty and delete a bucket to finish the remaining cleanup steps.

Prevent recurrence

Apply an AbortIncompleteMultipartUpload lifecycle rule to every bucket that accepts large uploads. The rule automatically aborts uploads that have not completed within a number of days you specify, and removes the parts.

Bucket lifecycle policies: Automate cleanup of incomplete multipart uploads.
Empty and delete a bucket: Full procedure for removing a bucket and its contents.
s3:ListMultipartUploads: API reference.
s3:AbortMultipartUpload: API reference.

​Prerequisites

​List incomplete multipart uploads

​Abort a specific multipart upload

​Abort every incomplete multipart upload in a bucket

​Verify the bucket is clear

​Prevent recurrence

​Related

Prerequisites

List incomplete multipart uploads

Abort a specific multipart upload

Abort every incomplete multipart upload in a bucket

Verify the bucket is clear

Prevent recurrence

Related