Name: troubleshooting-s3-files
Author: aws

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 sl

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](https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3 files troubleshooting.html). 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 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. 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 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: 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: 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. 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](https://docs.aws.amazon.com/cli/latest/userguide/getting started install.html). 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 Additional Resources [S3 Files Troubleshooting](https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3 files troubleshooting.html) [S3 Files Best Practices](https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3 files best practices.html) [S3 Files Quotas](https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3 files quotas.html)