Troubleshooting & FAQ

❓ Troubleshooting & FAQ

This guide provides troubleshooting solutions for common issues, answers frequently asked questions, and offers tips for Asuswrt-Merlin community members and forum helpers.

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🔍 Diagnostic Checklist

If you encounter an issue running TAILCAT ZER0, run through this quick checklist:

1. Check JFFS Partition

Ensure /jffs is mounted and has sufficient free disk space:

df -h /jffs

Requirement: At least 15MB of free space.

2. Verify Internet & DNS Connectivity

Confirm your router can resolve domain names and establish outbound connections to GitHub and DERP relays:

curl -sI https://github.com | head -n 1
ping -c 3 1.1.1.1

3. Verify TailCat Engine Execution

Test whether the compiled engine binary runs without missing libraries or architecture mismatch:

/jffs/addons/tailcatzero/bin/tailcat --version

Expected: tailcat v0.6.0 (or newer).

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🛠️ Common Issues & Fixes

1. "Engine binary missing or cannot execute"

• Symptom: install.sh or tailcatzero reports: [✗] TailCat engine binary failed to execute.
• Cause: The wrong CPU architecture was detected or the downloaded binary was truncated due to a transient network timeout.
• Fix:
  1. Check your router's architecture: uname -m
  2. Run the updater to fetch a fresh binary:

     tailcatzero update

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2. "Connection timed out connecting to token from client"

• Symptom: Running tailcat ssh <TOKEN> on client hangs or prints connection timed out.
• Causes:
  • The session timer expired and the tunnel was automatically torn down.
  • Your client ISP blocks outbound UDP STUN packets and DERP TLS (port 443) fallback failed.
• Fix:
  1. On the router, verify the session is still active:

     tailcatzero status

  2. If the session expired, restart it: tailcatzero view.
  3. Ensure your client device is running the latest tailcat client:

     brew upgrade tailcat
     # or
     go install github.com/tailscale/tailcat/cmd/tailcat@latest

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3. "Command restricted in view-only mode"

• Symptom: Guest types a command in view-only mode and receives: [-] Command '<cmd>' is restricted in view-only mode.
• Cause: The command is not part of the default read-only inspection allowlist.
• Fix:
  • Guest can type request <cmd> (or reply y when prompted).
  • Host router administrator approves the command via TUI (P hotkey) or CLI (tailcatzero approve <id>).

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4. "QR Code is not displaying"

• Symptom: Pressing q in the session card shows a message that qrencode is not installed.
• Cause: The router does not have Entware's qrencode package installed.
• Fix: If you have Entware installed, simply run:

  opkg update && opkg install qrencode

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5. "WebGUI shows SSL certificate security warning"

• Symptom: Browsing https://localhost:8443 displays a browser warning: Your connection is not private.
• Explanation: Asuswrt-Merlin uses a self-signed SSL certificate by default. This is completely expected behavior.
• Fix: Click Advanced ➔ Proceed to localhost (unsafe) to open the login page. The connection remains fully encrypted through the WireGuard tunnel.

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6. "Service is already running prompt"

• Symptom: Launching a service from the menu displays: [!] Service 🆘 Remote Support Shell (Root) is already running (PID: 14205).
• Explanation: TAILCAT ZER0 detects that a background instance of this service is already active on the router:

  TAILCAT ZER0 v1.8.0              ╱|、
                                 (˚ˎ 。7
                                  |、˜〵
  Instant Tunnel Manager         じしˍ,)ノ

========================================================================

  [!] Service 🆘 Remote Support Shell (Root) is already running (PID: 14205).

  1. 👁️ View session card and token
  2. 🛑 Stop active session
  3. 🔄 Restart session                 Stop and launch with fresh token

========================================================================

  👁️ View (Default)  |  🛑 Stop  |  🔄 Restart  |  ↩️ Back: 

• Actions:
  • Press v or 1 (or Enter) to view the active session card and copy its token.
  • Press s or 2 to stop the running session immediately.
  • Press r or 3 to stop and cleanly restart the service with a fresh token.
  • Press b to cancel and return to the main dashboard.

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💬 Frequently Asked Questions (FAQ)

Q: Do I need a Tailscale account or credit card?

A: No. TAILCAT ZER0 uses Tailscale's open-source tailcat engine. It connects directly peer-to-peer using DERP relays for rendezvous without needing any user account, email address, or credit card.

Q: Does TAILCAT ZER0 replace Asuswrt-Merlin's built-in WireGuard or OpenVPN servers?

A: No. TAILCAT ZER0 is designed for ephemeral, on-demand management, file transfers, and remote assistance. It runs independently alongside your existing VPNs, WireGuard tunnels, and VPN Director routing without interfering with them.

Q: Does running TAILCAT ZER0 consume high CPU or RAM?

A: No. TailCat is written in Go and optimized for embedded Linux devices. When idle or routing small management sessions, it consumes minimal CPU (<1%) and roughly 15-25MB of RAM.

Q: Can I run multiple services at the same time?

A: Yes! TAILCAT ZER0 supports up to 5 concurrent services running in parallel (Root Shell, View Shell, File Receiver, SFTP, and WebGUI). Each service receives its own isolated WireGuard node and unique capability token.

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🤝 SNBForums & Helper Guide

If you help users troubleshoot their routers on forums like SNBForums:

Quick Snippet to Send to a User:

"To help diagnose this issue, please run this on your router:

curl -fsSL https://raw.githubusercontent.com/underd0se/tailcat-zero/main/install.sh | sh
tailcatzero view

Then PM me the connection token shown on your screen (e.g. tcXXXXXXXXXXXX). This gives me read-only diagnostic access (I cannot edit files, reboot, or change settings), and it will automatically shut itself down after 30 minutes."

Once connected, you can inspect:

sysinfo
logread
ip route
nvram get wan0_ipaddr
netstat -tulpn

If you need to run an extra command, type request <command> and the user can approve it on their screen with one key.