Troubleshooting S3 Files
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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
Download the skill as a ZIP:
https://autogineer.com/agent-skills/aws/troubleshooting-s3-files/downloadUnzip 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
awsCLI is available withs3filessubcommand supportYou 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
| Symptom | Category |
|---|---|
| mount.s3files: command not found | A: Client Installation |
| Connection timed out during mount | B: Network/Security Group |
| Mount hangs indefinitely (no timeout) | B: Network/Security Group |
| Access denied during mount | C: IAM Permissions |
| File system stuck in "creating" | C: IAM Permissions |
| Permission denied on file operations | C: IAM Permissions |
| Files not appearing in S3 after write | D: Synchronization |
| Files in .s3files-lost+found directory | E: Conflict Resolution |
| Slow reads or high latency | F: Performance |
| NFS server error | G: Encryption/KMS |
| DNS name resolution fails | H: 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 Linux3. 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 REGIONCross-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 2049Note: These SG troubleshooting steps also apply to EFS — use
aws efs describe-mount-targetsinstead.
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 REGIONCheck 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 REGION5. 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-valuesCommon ExportError values:
| Error | Fix |
|---|---|
| S3AccessDenied | File system IAM role lacks S3 write permissions |
| S3BucketNotFound | Bucket deleted or renamed |
| RoleAssumptionFailed | Trust policy misconfigured |
| EncryptionKeyInaccessible | KMS key disabled or permissions revoked |
| PathTooLong | File 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 enableDnsSupportBoth 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=trueTroubleshooting
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.confSecurity 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
- ATTRIBUTION.mdAdded by AutoGineer935 B
- LICENSELicence file added by AutoGineer9.9 KiB
- NOTICELicence file added by AutoGineer67 B
- SKILL.md7.0 KiB
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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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- aws/agent-toolkit-for-aws · skills/specialized-skills/storage-skills/troubleshooting-s3-files · commit 0a218f8
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- 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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