troubleshooting-efs
Diagnoses and resolves Amazon EFS issues including mount failures, NFS timeouts, permission errors, throughput problems, and burst credit exhaustion. Use when the user has an EFS file system that is not mounting, returning errors, performing slowly, or showing access denied.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/aws/agent-toolkit-for-aws --skill troubleshooting-efs- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads troubleshooting-efs automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Troubleshooting EFS
Overview
Domain expertise for diagnosing and resolving Amazon EFS issues. Covers mount failures, NFS connectivity, IAM and POSIX permissions, throughput and performance, and encryption problems.
For authoritative guidance, see EFS Troubleshooting.
Common Tasks
0. Verify Dependencies
- You MUST verify
awsCLI is available - You MUST check if
amazon-efs-utilsornfs-utilsis installed on the instance - 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 what each step does and why before executing it
- You SHOULD display write commands and wait for user confirmation before executing
1. Classify the Issue
| Symptom | Category |
|---|---|
| "wrong fs type" or mount command fails | A: Missing NFS Client |
| Connection timed out (hangs 2+ min) | B: Network/Security Group |
| "access denied by server" | C: IAM/Permissions |
| Slow throughput or high latency | D: Performance |
| NFS server error on encrypted FS | E: Encryption/KMS |
| DNS name resolution fails | F: VPC DNS |
2. Category A — Missing NFS Client
# Amazon Linux / RHEL / CentOS
sudo yum -y install amazon-efs-utils # preferred (includes mount helper + TLS)
# OR
sudo yum -y install nfs-utils
# Ubuntu / Debian
sudo apt-get install nfs-common
3. Category B — Network/Security Group
Connection timeout is the #1 EFS mount failure — almost always security groups.
- Verify mount target exists in the instance's AZ:
aws efs describe-mount-targets --file-system-id fs-ID --region REGION
-
Verify security groups — check BOTH directions:
- Mount target SG:
aws ec2 describe-security-groups --group-ids sg-MT— MUST have inbound TCP 2049 from compute SG - Compute SG: MUST have outbound TCP 2049 to mount target SG
- Quick fix:
aws ec2 authorize-security-group-ingress --group-id sg-MT --protocol tcp --port 2049 --source-group sg-COMPUTE
- Mount target SG:
-
Test connectivity:
nc -zv fs-ID.efs.REGION.amazonaws.com 2049
Note: These security group troubleshooting steps also apply to S3 Files. The only difference is S3 Files uses
aws s3files list-mount-targetsinstead ofaws efs describe-mount-targets.
4. Category C — IAM/Permissions
"access denied by server" with -o iam:
- Check identity-based IAM policy has
elasticfilesystem:ClientMount - Check file system resource policy:
aws efs describe-file-system-policy --file-system-id fs-ID --region REGION
Note: IAM authorization is only enforced when a file system policy exists that requires it. Without a file system policy, any client in the VPC with port 2049 access can mount — even with -o iam. To enforce IAM, you MUST create a file system policy that denies anonymous access.
POSIX permission denied (not IAM):
- Check file/directory ownership:
ls -la /mnt/efs/ - Use access points to enforce UID/GID for consistent permissions
5. Category D — Performance
Check throughput mode:
aws efs describe-file-systems --file-system-id fs-ID --region REGION --query 'FileSystems[0].ThroughputMode'
Burst credit exhaustion (Bursting mode only):
aws cloudwatch get-metric-statistics --namespace AWS/EFS --metric-name BurstCreditBalance --dimensions Name=FileSystemId,Value=fs-ID --period 3600 --statistics Average --start-time $(date -u -d '24 hours ago' +%Y-%m-%dT%H:%M:%S) --end-time $(date -u +%Y-%m-%dT%H:%M:%S)
If credits near zero, switch to Elastic throughput:
aws efs update-file-system --file-system-id fs-ID --throughput-mode elastic --region REGION
General Purpose vs Max I/O:
- Check
PercentIOLimitmetric — if consistently >80%, consider Max I/O - Note: performance mode is IMMUTABLE — must create new FS and migrate
6. Category E — Encryption/KMS
NFS server error on encrypted FS = KMS key issue.
- Verify key is enabled in KMS console
- Verify EFS service-linked role has KMS permissions
- If key deleted: cancel deletion if within grace period
7. Category F — 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
Mount hangs then times out
Most common cause: security group. Verify TCP 2049 is open between compute and mount target.
Auto-mount fails on reboot
/etc/fstab entry MUST include _netdev option to wait for network before mounting.
"nfs not responding" after reconnect
Old kernel bug with TCP port reuse. Update kernel or add noresvport mount option.
Enable Debug Logs
Set logging_level = DEBUG in /etc/amazon/efs/efs-utils.conf. Logs at /var/log/amazon/efs/mount.log.
Collect Logs for AWS Support
sudo tar -czf /tmp/efs-logs.tar.gz /var/log/amazon/efs/ /etc/amazon/efs/efs-utils.conf
Security Considerations
- IAM authorization is only enforced when a file system policy exists — without one, any VPC client with port 2049 access can mount
- When troubleshooting access denied, verify both identity-based and resource-based policies
- Use
-o tlsfor encryption in transit — unencrypted NFS traffic is visible on the network - Restrict
/var/log/amazon/efs/access — logs may contain file system IDs and mount target IPs
Additional Resources
FAQ
What does the troubleshooting-efs skill do?
Diagnoses and resolves Amazon EFS issues including mount failures, NFS timeouts, permission errors, throughput problems, and burst credit exhaustion. Use when the user has an EFS file system that is not mounting, returning errors, performing slowly, or showing access denied.
How do I install troubleshooting-efs?
Run npx skills add https://github.com/aws/agent-toolkit-for-aws --skill troubleshooting-efs in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/troubleshooting-efs/ (personal) or .claude/skills/troubleshooting-efs/ (project).
Which AI agents can use troubleshooting-efs?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is troubleshooting-efs safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains troubleshooting-efs?
It is published by aws in aws/agent-toolkit-for-aws, and it is an official skill from the maker of the technology it covers. It has 5,954 recorded installs.
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