Browser Troubleshooting (Linux)

Problem: “Failed to start Chrome CDP on port 18800”

Moltbot’s browser control server fails to launch Chrome/Brave/Edge/Chromium with the error:


{"error":"Error: Failed to start Chrome CDP on port 18800 for profile \"clawd\"."}

Root Cause

On Ubuntu (and many Linux distros), the default Chromium installation is a snap package. Snap’s AppArmor confinement interferes with how Moltbot spawns and monitors the browser process.The apt install chromium command installs a stub package that redirects to snap:


Note, selecting 'chromium-browser' instead of 'chromium'
chromium-browser is already the newest version (2:1snap1-0ubuntu2).

This is NOT a real browser — it’s just a wrapper.

Solution 1: Install Google Chrome (Recommended)

Install the official Google Chrome .deb package, which is not sandboxed by snap:


wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
sudo dpkg -i google-chrome-stable_current_amd64.deb
sudo apt --fix-broken install -y  # if there are dependency errors

Then update your Moltbot config (~/.clawdbot/moltbot.json):


{
  "browser": {
    "enabled": true,
    "executablePath": "/usr/bin/google-chrome-stable",
    "headless": true,
    "noSandbox": true
  }
}

Solution 2: Use Snap Chromium with Attach-Only Mode

If you must use snap Chromium, configure Moltbot to attach to a manually-started browser:

Update config:


{
  "browser": {
    "enabled": true,
    "attachOnly": true,
    "headless": true,
    "noSandbox": true
  }
}

Start Chromium manually:


chromium-browser --headless --no-sandbox --disable-gpu \
  --remote-debugging-port=18800 \
  --user-data-dir=$HOME/.clawdbot/browser/clawd/user-data \
  about:blank &

Optionally create a systemd user service to auto-start Chrome:


# ~/.config/systemd/user/clawd-browser.service
[Unit]
Description=Clawd Browser (Chrome CDP)
After=network.target

[Service]
ExecStart=/snap/bin/chromium --headless --no-sandbox --disable-gpu --remote-debugging-port=18800 --user-data-dir=%h/.clawdbot/browser/clawd/user-data about:blank
Restart=on-failure
RestartSec=5

[Install]
WantedBy=default.target

Enable with: systemctl --user enable --now clawd-browser.service

Verifying the Browser Works

Check status:


curl -s http://127.0.0.1:18791/ | jq '{running, pid, chosenBrowser}'

Test browsing:


curl -s -X POST http://127.0.0.1:18791/start
curl -s http://127.0.0.1:18791/tabs

Config Reference

Option	Description	Default
`browser.enabled`	Enable browser control	`true`
`browser.executablePath`	Path to a Chromium-based browser binary (Chrome/Brave/Edge/Chromium)	auto-detected (prefers default browser when Chromium-based)
`browser.headless`	Run without GUI	`false`
`browser.noSandbox`	Add `--no-sandbox` flag (needed for some Linux setups)	`false`
`browser.attachOnly`	Don’t launch browser, only attach to existing	`false`
`browser.cdpPort`	Chrome DevTools Protocol port	`18800`

Problem: “Chrome extension relay is running, but no tab is connected”

You’re using the chrome profile (extension relay). It expects the Moltbot browser extension to be attached to a live tab.Fix options:

Use the managed browser:moltbot browser start --browser-profile clawd (or set browser.defaultProfile: "clawd").
Use the extension relay: install the extension, open a tab, and click the Moltbot extension icon to attach it.

Notes:

The chrome profile uses your system default Chromium browser when possible.
Local clawd profiles auto-assign cdpPort/cdpUrl; only set those for remote CDP.