MCP Server Fails to Start — spawn ENOENT Error on Startup

Symptom

MCP server shows spawn ENOENT error on agent startup
Agent starts but the tool/server is unavailable
No error if the server command is run manually in the same shell
Error appears in agent logs, not in shell output

Root Cause

ENOENT (No such file or directory) on spawn means the executable path doesn’t exist in the environment the agent runs in. The agent process has a different PATH than your interactive shell — especially when run via systemd, Docker, or npm start.

Fix

Option 1: Use absolute path in MCP config

{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/mcp-server-filesystem",
      "args": ["--root", "/workspace"]
    }
  }
}

Find the absolute path:

which mcp-server-filesystem
# → /usr/local/bin/mcp-server-filesystem

Option 2: Use npx to resolve path automatically

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/workspace"]
    }
  }
}

npx handles path resolution — the server doesn’t need to be in PATH.

Option 3: Pass explicit PATH to the MCP server process

{
  "mcpServers": {
    "filesystem": {
      "command": "mcp-server-filesystem",
      "args": ["--root", "/workspace"],
      "env": {
        "PATH": "/usr/local/bin:/usr/bin:/bin"
      }
    }
  }
}

Option 4: Install globally and verify

npm install -g @modelcontextprotocol/server-filesystem

# Verify it's accessible
mcp-server-filesystem --help

# If still not found after global install, check npm prefix
npm config get prefix
# Add <prefix>/bin to PATH in your shell profile

Diagnosis

# Check if the server is installed
npm list -g | grep mcp

# Check all candidate locations
find /usr -name "mcp-server-*" 2>/dev/null
find ~/.npm -name "mcp-server-*" 2>/dev/null

# Test spawn manually (same as agent would)
node -e "require('child_process').spawn('mcp-server-filesystem', [], {stdio: 'inherit'})"

Expected Token Savings

Debugging missing MCP server tool at runtime: ~4,000 tokens This fix: ~100 tokens (one config line change)

Environment

OpenClaw with MCP server configuration
Any Node.js-based MCP server
Affects startup when PATH differs between shell and agent process
Source: direct experience, common MCP setup issue

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