Fix clw-sandbox-limit-exceeded: OpenClaw sandbox resource limits exceeded

1. Symptoms

The clw-sandbox-limit-exceeded error occurs in OpenClaw, the runtime environment for Claw programs executed in a sandboxed mode. This error halts execution when the program surpasses predefined resource quotas designed to prevent abuse, denial-of-service, or infinite loops in constrained environments like web servers, CI/CD pipelines, or multi-tenant systems.

Typical manifestations include:

$ clw run --sandbox sandboxed_app.clw
Error: clw-sandbox-limit-exceeded
Sandbox CPU time limit exceeded: 500ms wall-clock time.
Program terminated at instruction 0x7f8a2b3c: loop iteration 1,000,000.
Metrics: CPU: 520ms, Memory: 128MiB peak, Allocations: 50k.

$ clw sandbox exec --limit-cpu=100ms example.clw
[Sandbox] Initializing with limits: CPU=100ms, Mem=64MiB, FD=1024
[Sandbox] Violation: clw-sandbox-limit-exceeded (CPU)
Peak usage: CPU=105ms, Mem=32MiB
Exit code: 137

In verbose mode (clw run -v), additional diagnostics appear:

[DEBUG] Sandbox monitor: CPU usage spiked to 120% of limit.
[DEBUG] Halting PID 12345 due to quota breach.
Error: clw-sandbox-limit-exceeded

Symptoms often coincide with:

• Programs hanging or timing out unexpectedly.
• High CPU utilization visible in top or htop.
• No output or partial results before abrupt termination.
• Logs indicating “sandbox violation” in containerized setups (e.g., Docker with OpenClaw).

This error is common in Claw applications with tight loops, recursive functions without tail optimization, excessive allocations, or I/O-bound operations in sandboxed contexts.

2. Root Cause

OpenClaw’s sandbox enforces strict resource limits to ensure safe, predictable execution. Limits are configurable via CLI flags (--limit-cpu, --limit-mem) or config files (sandbox.toml), with defaults suited for untrusted code:

The error triggers when any quota is breached. Root causes include:

1. Inefficient Algorithms: Nested loops or naive recursion exceeding CPU limits.

   // Example: Infinite-like loop
   fn factorial(n: u64) -> u64 {
       if n == 0 { 1 } else { n * factorial(n - 1) }
   }
   fn main() {
       let _ = factorial(10000); // Stack overflow + CPU burn
   }
   

2. Memory Leaks: Repeated allocations without deallocation in safe pointers.

3. I/O Overuse: Polling files or sockets in tight loops.

4. Misconfigured Limits: Defaults too low for legitimate workloads.

5. External Factors: Host resource contention amplifying sandbox throttling.

Internally, OpenClaw uses seccomp-BPF (Linux), pledge (OpenBSD), or WASM runtimes for enforcement. The monitor thread polls metrics every 10ms, signaling SIGTERM on breach.

3. Step-by-Step Fix

Step 1: Diagnose the Specific Limit

Run with metrics:

clw run --sandbox --metrics sandboxed_app.clw

Identify the breached resource (e.g., CPU).

Step 2: Optimize Code for Efficiency

Before: Inefficient recursive factorial causing CPU limit hit.

// factorial.clw - BEFORE: Deep recursion burns CPU
fn factorial(n: u64) -> u64 {
    match n {
        0 => 1,
        _ => n * factorial(n - 1),
    }
}

fn main() {
    let result = factorial(5000); // Exceeds 500ms CPU
    io::println("Result: {}", result);
}

$ clw run --sandbox factorial.clw
Error: clw-sandbox-limit-exceeded
Sandbox CPU time limit exceeded: 520ms.

After: Iterative version with loop unrolling.

// factorial.clw - AFTER: Iterative, O(n) time
fn factorial(n: u64) -> u64 {
    let mut result = 1u64;
    let mut i = 1u64;
    while i <= n {
        result *= i;
        i += 1;
        // Optional: Early exit for large n to avoid overflow
        if result > u64::MAX / i { break; }
    }
    result
}

fn main() {
    let result = factorial(5000);
    io::println("Result: {}", result);
}

$ clw run --sandbox factorial.clw
Result: 5000! (computed in 2ms)

Step 3: Reduce Memory Footprint

Use stack allocation over heap: Before:

fn allocate_loop(iter: usize) {
    for i in 0..iter {
        let vec = alloc::vec::with_capacity(1_000_000); // Heap churn
    }
}

After:

fn allocate_loop(iter: usize) {
    let mut buf = [0u8; 1_000_000]; // Stack or static
    for i in 0..iter {
        // Reuse buffer
        buf.fill(i as u8);
    }
}

Step 4: Adjust Sandbox Limits (Temporary)

clw run --sandbox --limit-cpu=2s --limit-mem=512MiB app.clw

Or in sandbox.toml:

[limits]
cpu_ms = 2000
mem_mb = 512
fd_max = 2048

Step 5: Disable Sandbox for Trusted Code

clw run --no-sandbox app.clw

⚠️ Use only for trusted binaries.

Step 6: Profile with Tools

clw profile --sandbox app.clw > profile.json

Analyze hotspots.

4. Verification

1. Re-run the sandboxed command:

   $ clw run --sandbox --metrics app.clw
   [Sandbox] All limits OK. CPU: 45ms/500ms, Mem: 64MiB/256MiB
   Program exited successfully.
   

2. Stress test:

   for i in {1..100}; do clw run --sandbox app.clw; done
   

   Expect 100% success rate.

3. Monitor metrics:

   • CPU: perf stat clw run --sandbox app.clw
   • Memory: valgrind --tool=massif clw run app.clw (non-sandboxed for leaks).

4. Integration test in CI:

   # .github/workflows/test.yml
   - name: Sandbox Test
     run: clw run --sandbox tests/integration.clw
   

Success: No clw-sandbox-limit-exceeded, metrics under 80% of limits.

5. Common Pitfalls

• Over-Reliance on Recursion: Claw lacks automatic tail-call optimization; always prefer iteration.

  // Pitfall: This still fails
  fn fib_rec(n: u64) -> u64 { /* naive fib */ }
  

• Ignoring Metrics: Running without --metrics hides the exact limit (CPU vs. mem).

• Increasing Limits Blindly: Masks bugs; optimize first.

• Platform Differences: macOS sandbox uses different clocks; test cross-platform.

  $ clw run --sandbox app.clw  # macOS: May report "wall-clock" vs Linux "user+sys"
  

• Heap Allocations in Loops: Use arenas or pools.

  // Bad
  loop { let _ = Box::new([0u8; 1<<20]); }
  

• Async Code: Coroutines can amplify CPU if not yielding properly.

• Static Linking Oversights: Large binaries inflate memory baseline.

• Config File Precedence: CLI flags override sandbox.toml; check with clw sandbox info.

6. Related Errors

Cross-reference these for multi-resource issues. For deeper dives, see OpenClaw docs: clw sandbox --help.

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