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prime-rl uses loguru for logging with a global logger pattern. All logs are captured at the deployment level (stdout/stderr redirection for local, tee for SLURM) under {output_dir}/logs/. For RL training, we recommend streaming logs into tmux panes (as set up by tmux.sh).

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Logger Architecture

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setup_logger and get_logger

We use a singleton pattern with a module-level global logger instance (_LOGGER). 
from prime_rl.utils.logger import setup_logger, get_logger

# At entrypoint - call ONCE
logger = setup_logger("info")

# Anywhere else in codebase
logger = get_logger()
logger.info("Hello world")
How it works:
  1. get_logger() - Returns the global logger instance. Always works — if setup_logger hasn’t been called yet, it initializes a default logger automatically. Safe to call from any module at any time.
  2. setup_logger(log_level) - Configures (or reconfigures) the global logger:
    • Creates an isolated loguru Logger instance (not the default loguru.logger) to prevent third-party code from hijacking our logs
    • Adds a stdout handler with colorized output (or JSON output if json_logging=True)
    • Can be called multiple times — cleans up the previous logger before creating a new one
  3. reset_logger() - Resets the global logger to None:
    • Used in subprocesses that inherit parent state (e.g., env workers)
    • Used in tests between test cases

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Log File Structure

Logs are captured at the deployment level — the entrypoint redirects subprocess stdout/stderr to files (local) or tee captures them (SLURM). The structure is consistent across deployment types: logs/trainer.log and logs/inference.log always exist, regardless of whether the run is local or multi-node SLURM.

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Local (single node)

{output_dir}/logs/
├── trainer.log                  # trainer stdout (rank 0 only)
├── orchestrator.log             # orchestrator stdout
├── inference.log                # vLLM inference server stdout
├── trainer/
│   └── torchrun/                # per-rank stdout/stderr (all ranks)
└── envs/
    ├── train/{env_name}/
    │   ├── env_server.log
    │   └── env_worker_{id}.log
    └── eval/{env_name}/
        └── ...

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SLURM multi-node

{output_dir}/logs/
├── trainer.log                  -> trainer/node_0.log (symlink)
├── inference.log                -> inference/node_0.log (symlink)
├── orchestrator.log             # orchestrator stdout
├── trainer/
│   ├── node_0.log               # per-node trainer output (rank 0 only)
│   ├── node_1.log
│   └── torchrun/                # per-rank stdout/stderr (all ranks)
├── inference/
│   ├── node_0.log               # per-node inference output
│   ├── node_1.log
│   └── router_0.log             # vllm-router per replica
└── envs/
    └── ...
Environment logs live under logs/envs/train/{env_name}/ and logs/envs/eval/{env_name}/. Env log verbosity is controlled by orchestrator.log.vf_level. Only rank 0 output is shown in trainer.log. Per-rank logs from all ranks are available under logs/trainer/torchrun/{rdzv_id}/attempt_0/{rank}/{stdout,stderr}.log, written by torchrun’s --log-dir.

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tmux helper (scripts/tmux.sh)

scripts/tmux.sh sets up a tmux session for RL runs with four panes:
  • Trainer: follows {output_dir}/logs/trainer.log
  • Orchestrator: follows {output_dir}/logs/orchestrator.log
  • Envs: follows {output_dir}/logs/envs/*/*/*.log
  • Inference: follows {output_dir}/logs/inference.log