> ## Documentation Index
> Fetch the complete documentation index at: https://docs.coreweave.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Sandbox logging

> Stream container logs (stdout and stderr) from a sandbox's main process with stream_logs().

This guide shows how to capture container logs from a sandbox so you can monitor what your main process does, debug failures, or inspect output after a sandbox stops.

Container logs are stdout and stderr from a sandbox's **main process**. Stream them with `stream_logs()`, which captures output from the command passed to `Sandbox.run()`. Output from `exec()` commands isn't included. Use `Process.stdout` or `Process.stderr` for that.

`stream_logs()` returns a `StreamReader` that yields log lines. Iterate synchronously or asynchronously.

<Note>
  When you call `Sandbox.run()` without a command, the sandbox's default command doesn't write to stdout or stderr, so `stream_logs()` returns no output. Pass a command that writes to stdout or stderr.
</Note>

## Retrieve recent logs

Use `tail_lines` to fetch the most recent log lines without streaming the entire history. This is useful for quick inspection of a running sandbox.

```python theme={"system"}
for line in sandbox.stream_logs(tail_lines=100):
    print(line, end="")
```

## Follow mode

Stream logs continuously, like `tail -f`. The iterator blocks until new data arrives.

```python theme={"system"}
for line in sandbox.stream_logs(follow=True):
    print(line, end="")
```

Press `Ctrl+C` to stop when iterating in follow mode.

## Filter by time

Pass `since_time` to retrieve only logs after a specific timestamp. This narrows output to a window of interest, such as logs since a deployment or incident.

```python theme={"system"}
from datetime import datetime, timezone

since = datetime(2026, 2, 20, 14, 0, 0, tzinfo=timezone.utc)
for line in sandbox.stream_logs(since_time=since):
    print(line, end="")
```

## Timestamps

Set `timestamps=True` to prefix each line with an ISO 8601 timestamp from the server. Server-side timestamps help correlate sandbox events with other systems.

```python theme={"system"}
for line in sandbox.stream_logs(tail_lines=10, timestamps=True):
    print(line, end="")
# Output: 2026-02-20T14:30:00Z some log line
```

## Async iteration

If your application uses `asyncio`, iterate over the same `StreamReader` with `async for` to avoid blocking the event loop.

```python theme={"system"}
async for line in sandbox.stream_logs(follow=True):
    print(line, end="")
```

## Retrieve logs from stopped sandboxes

Logs remain available after a sandbox stops, which lets you investigate failures or review output from completed work. Retrieve historical logs from sandboxes that completed, failed, or terminated:

```python theme={"system"}
sb = Sandbox.from_id("sbx-abc123").result()
for line in sb.stream_logs(tail_lines=50):
    print(line, end="")
```

Stopped sandboxes support only `follow=False` (the default).

## See also

* [Command execution](/products/sandboxes/client/guides/execution): Running commands and streaming their output with `exec()`
* [Sync vs async](/products/sandboxes/client/guides/sync-vs-async): Iteration patterns