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 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
2. Category A — Client Installation
mount.s3files: command not found means amazon-efs-utils is missing or < v3.0.0.
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:
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:
Note: 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:
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:
5. Category D — Synchronization
Files not appearing in S3: Writes sync within ~60 seconds. Check status:
Common ExportError values:
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.
Both MUST be true. If not:
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
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
