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Troubleshooting S3 Files

AWSOfficialPublished by AWS

  • Skill
  • Review and audit
  • Cloud and DevOps
  • Apache-2.0
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From the author

Diagnoses and resolves Amazon S3 Files issues including mount failures, permission errors, synchronization problems, and performance issues. Use when the user has an S3 file system that is not mounting, returning access denied, not syncing changes to S3, showing files in lost+found, or performing slower than expected.
— the description by AWS

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a structured troubleshooting framework for Amazon S3 Files. It helps users identify and resolve common operational failures, including mount errors, IAM permission issues, synchronization conflicts, and performance bottlenecks. The guide covers diagnostic steps for network configurations, VPC settings, and CLI-based verification to ensure S3 Files environments are correctly deployed and maintained.

What it does

  • Classifies S3 Files issues based on specific error symptoms.
  • Provides commands to verify AWS CLI dependencies and credentials.
  • Guides users through network and security group configuration checks.
  • Details IAM permission requirements for mounting and file operations.
  • Explains how to resolve synchronization conflicts and performance latency.
  • Offers instructions for enabling debug logs and collecting diagnostic data for support.

When to use it

  • When an S3 file system fails to mount or hangs during the process.
  • When encountering access denied errors during file operations.
  • When files are not appearing in S3 or synchronization appears stalled.
  • When experiencing slower than expected read or write performance.
  • When files unexpectedly appear in the lost+found directory.

Advantages

  • Provides a clear mapping of symptoms to specific technical categories.
  • Includes actionable CLI commands for rapid diagnosis.
  • Emphasizes security best practices like least-privilege IAM policies.
  • Helps distinguish S3 Files from similar AWS storage services.
  • Standardizes the process for collecting logs for AWS support.

Usage examples

“My S3 file system is stuck in the creating status, what should I check?”
The agent will guide you to use the get-file-system command to check the statusMessage and verify if the IAM role has the necessary permissions.
“I am getting a connection timeout when trying to mount my S3 file system.”
The agent will help you verify security group rules, specifically checking for inbound and outbound TCP 2049 traffic between the compute instance and the mount target.

Install

  1. Download the skill as a ZIP:

    https://autogineer.com/agent-skills/aws/troubleshooting-s3-files/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip troubleshooting-s3-files.zip -d .agents/skills

Documentation by AWS

Troubleshooting S3 Files

Overview

Diagnoses and resolves Amazon S3 Files issues: mount failures, IAM permissions, synchronization, conflict resolution, and performance.

For authoritative guidance, see S3 Files Troubleshooting.

Common Tasks

0. Verify Dependencies
  • You MUST verify aws CLI is available with s3files subcommand support

  • You MUST confirm valid AWS credentials

  • You MUST ONLY check for tool existence and version — MUST NOT execute destructive or mutating commands during verification

  • You MUST inform the user if any required tools are missing

  • You MUST respect the user's decision to abort if tools are unavailable

  • You SHOULD explain steps before executing and wait for user confirmation on write commands

1. Classify the Issue
SymptomCategory
mount.s3files: command not foundA: Client Installation
Connection timed out during mountB: Network/Security Group
Mount hangs indefinitely (no timeout)B: Network/Security Group
Access denied during mountC: IAM Permissions
File system stuck in "creating"C: IAM Permissions
Permission denied on file operationsC: IAM Permissions
Files not appearing in S3 after writeD: Synchronization
Files in .s3files-lost+found directoryE: Conflict Resolution
Slow reads or high latencyF: Performance
NFS server errorG: Encryption/KMS
DNS name resolution failsH: VPC DNS
2. Category A — Client Installation

mount.s3files: command not found means amazon-efs-utils is missing or < v3.0.0.

sudo yum -y install amazon-efs-utils  # Amazon Linux
3. Category B — Network/Security Group

Connection timeout is the #1 mount failure — almost always security groups.

Verify mount target exists in the instance's AZ:

aws s3files list-mount-targets --file-system-id fs-ID --region REGION

Cross-AZ mounting works but adds latency.

Verify security groups — most common fix:

  • Mount target SG MUST have inbound TCP 2049 from compute SG

  • Compute SG MUST have outbound TCP 2049 to mount target SG

  • Fix: aws ec2 authorize-security-group-ingress --group-id sg-MT --protocol tcp --port 2049 --source-group sg-COMPUTE

Test connectivity:

nc -zv az-ID.fs-ID.s3files.REGION.on.aws 2049

Note: These SG troubleshooting steps also apply to EFS — use aws efs describe-mount-targets instead.

Mount hangs in isolated VPC: If the VPC has no internet access, S3 Files requires a CloudWatch Logs VPC endpoint (com.amazonaws.REGION.logs) for mount to complete.

4. Category C — IAM Permissions

File system stuck in "creating" status: S3 Files does NOT validate IAM role permissions at creation time. Wrong trust policy or missing permissions → stuck in creating with access denied in statusMessage.

Check status:

aws s3files get-file-system --file-system-id fs-ID --region REGION

Check statusMessage. If access denied, fix the IAM role and delete/recreate.

Mount access denied: Compute role needs s3files:ClientMount. For dev/test only, AmazonS3FilesClientFullAccess is acceptable — avoid in production.

Write permission denied: Compute role needs s3files:ClientWrite

Root access denied: Compute role needs s3files:ClientRootAccess. ⚠️ Bypasses POSIX permissions — prefer access points with scoped POSIX users.

Check file system policy:

aws s3files get-file-system-policy --file-system-id fs-ID --region REGION
5. Category D — Synchronization

Files not appearing in S3: Writes sync within ~60 seconds. Check status:

getfattr -n "user.s3files.status;$(date -u +%s)" filename --only-values

Common ExportError values:

ErrorFix
S3AccessDeniedFile system IAM role lacks S3 write permissions
S3BucketNotFoundBucket deleted or renamed
RoleAssumptionFailedTrust policy misconfigured
EncryptionKeyInaccessibleKMS key disabled or permissions revoked
PathTooLongFile path exceeds 1,024 byte S3 key limit

Monitor: PendingExports CloudWatch metric. Growing = exceeds 800 files/sec rate.

6. Category E — Conflict Resolution

Files in .s3files-lost+found-{fs-id} = sync conflict (modified via FS and S3 simultaneously). S3 wins; FS version moved to lost+found.

7. Category F — Performance

First access latency: Normal — first directory access imports metadata.

Intelligent read routing not working: Compute role needs s3:GetObject on the bucket.

Slow writes: If PendingExports growing, distribute across multiple file systems.

8. Category G — Encryption/KMS

NFS server error with encrypted FS = KMS issue. Verify key is enabled and role has KMS permissions.

9. Category H — VPC DNS

DNS resolution failure = VPC DNS settings disabled.

aws ec2 describe-vpc-attribute --vpc-id vpc-ID --attribute enableDnsHostnames
aws ec2 describe-vpc-attribute --vpc-id vpc-ID --attribute enableDnsSupport

Both MUST be true. If not:

aws ec2 modify-vpc-attribute --vpc-id vpc-ID --enable-dns-hostnames Value=true
aws ec2 modify-vpc-attribute --vpc-id vpc-ID --enable-dns-support Value=true

Troubleshooting

AWS CLI endpoint URL cannot be resolved

CLI is too old for S3 Files. Run aws --version — if v1.x, upgrade to AWS CLI v2: Installing the AWS CLI.

ECS task fails with DNS resolution error

Used efsVolumeConfiguration instead of s3filesVolumeConfiguration. Fix: use fileSystemArn in S3 Files-specific volume config.

S3 Files vs other products confusion

S3 Files is NOT Mountpoint for S3, S3 File Gateway, or File Cache. Uses aws s3files CLI, s3files: IAM actions, mount -t s3files.

Enable Debug Logs

Set logging_level = DEBUG in /etc/amazon/efs/s3files-utils.conf. Logs at /var/log/amazon/efs/mount.log.

Collect Logs for AWS Support
sudo tar -czf /tmp/s3files-logs.tar.gz /var/log/amazon/efs/ /etc/amazon/efs/s3files-utils.conf

Security Considerations

  • When diagnosing IAM issues, verify least-privilege — avoid FullAccess as a shortcut

  • Without a file system policy, any VPC client can mount

  • Restrict /var/log/amazon/efs/ access — logs contain S3 key names

Additional Resources

Files

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Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

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Attribution and licence

Published by
AWS
Publisher
AWS (Official)
Source
aws/agent-toolkit-for-aws · skills/specialized-skills/storage-skills/troubleshooting-s3-files · commit 0a218f8
Licence
Apache License 2.0 (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE)
  • NOTICE (added by AutoGineer from NOTICE)
  • ATTRIBUTION.md (written by AutoGineer)
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