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Agent Environment Variables Not Available in Subprocess — Missing Config

Symptom

• Agent sets os.environ["API_KEY"] = value but a spawned subprocess exits with API_KEY not set
• Docker container env vars visible in Python but missing in subprocess.run(["bash", "script.sh"])
• Shell script run via subprocess can’t find DATABASE_URL that was passed to the container
• subprocess.Popen with shell=False doesn’t expand environment variables from parent
• exec() call inside subprocess uses a clean environment — missing all parent env vars
• Environment variable set in one thread not visible in subprocess spawned by another thread

Root Cause

Subprocess environment inheritance depends on how the subprocess is launched. By default, subprocess.run() inherits the parent process environment — but only what was in os.environ at the time of the call, not variables set afterward in ways that bypass os.environ. env={} or env={"KEY": "value"} (without merging parent env) creates a completely clean environment. In Docker, variables must be declared in the Dockerfile or docker-compose — simply setting them in the entrypoint script may not propagate to all processes.

Fix

Option 1: Always merge parent environment when customizing subprocess env

import subprocess
import os

# WRONG — completely replaces env, subprocess loses all parent vars
result = subprocess.run(
    ["python3", "worker.py"],
    env={"MY_CUSTOM_VAR": "value"},  # Subprocess has ONLY this var
    capture_output=True
)

# WRONG — subprocess.run() with no env= inherits parent,
# but only if API_KEY was set before the Python process started
# (not effective for keys set via os.environ later in the script)

# RIGHT — inherit parent env AND add custom vars
subprocess_env = {**os.environ, "MY_CUSTOM_VAR": "value"}
result = subprocess.run(
    ["python3", "worker.py"],
    env=subprocess_env,
    capture_output=True,
    text=True
)

# RIGHT — inherit and override specific vars:
def run_subprocess(cmd: list[str], extra_env: dict = None) -> subprocess.CompletedProcess:
    """
    Run subprocess with parent environment + optional overrides.
    Guarantees all parent env vars are available to the subprocess.
    """
    env = dict(os.environ)  # Copy current env
    if extra_env:
        env.update(extra_env)

    return subprocess.run(
        cmd,
        env=env,
        capture_output=True,
        text=True,
        timeout=60
    )

# Usage:
result = run_subprocess(
    ["bash", "deploy.sh"],
    extra_env={"DEPLOY_ENV": "staging", "DRY_RUN": "false"}
)

Option 2: Set env vars before subprocess launch using os.environ

import os
import subprocess

def configure_subprocess_env(required_vars: dict[str, str], optional_vars: dict[str, str] = None):
    """
    Ensure all required environment variables are set in os.environ
    before spawning subprocesses.
    Validates required vars — fails fast if missing.
    """
    missing = []
    for key, description in required_vars.items():
        if key not in os.environ:
            missing.append(f"  {key}: {description}")

    if missing:
        raise EnvironmentError(
            "Missing required environment variables for subprocess:\n" +
            "\n".join(missing) +
            "\n\nSet these before running the agent."
        )

    # Apply optional vars with defaults if not already set
    if optional_vars:
        for key, default_value in optional_vars.items():
            if key not in os.environ:
                os.environ[key] = default_value
                print(f"Set default: {key}={default_value}")

# Call at startup — before spawning any subprocess:
configure_subprocess_env(
    required_vars={
        "API_KEY": "Anthropic API key for model calls",
        "DATABASE_URL": "PostgreSQL connection string",
    },
    optional_vars={
        "LOG_LEVEL": "INFO",
        "WORKER_TIMEOUT": "60",
    }
)

# Now subprocesses inherit all vars from os.environ:
result = subprocess.run(["python3", "worker.py"], capture_output=True, text=True)

Option 3: Explicit env file for subprocess isolation

import os
import tempfile
import subprocess
from pathlib import Path

def create_env_file(variables: dict[str, str]) -> str:
    """
    Write environment variables to a temp .env file.
    Subprocess loads this file — works even across exec() boundaries.
    """
    lines = []
    for key, value in variables.items():
        # Escape special characters in value
        escaped = value.replace("'", "'\\''")
        lines.append(f"export {key}='{escaped}'")

    content = "\n".join(lines)
    tmp = tempfile.NamedTemporaryFile(mode='w', suffix='.env', delete=False)
    tmp.write(content)
    tmp.close()
    return tmp.name

def run_script_with_env(script_path: str, env_vars: dict[str, str]) -> subprocess.CompletedProcess:
    """
    Run a shell script with explicit env vars — works even if script uses exec or su.
    """
    env_file = create_env_file(env_vars)

    try:
        # Source the env file before running the script
        cmd = ["bash", "-c", f"source {env_file} && bash {script_path}"]
        result = subprocess.run(cmd, capture_output=True, text=True, timeout=120)
        return result
    finally:
        os.unlink(env_file)  # Clean up temp file

# Pass secrets explicitly — don't rely on inheritance:
result = run_script_with_env(
    script_path="./scripts/process_data.sh",
    env_vars={
        "API_KEY": os.environ["API_KEY"],
        "DATABASE_URL": os.environ["DATABASE_URL"],
        "OUTPUT_DIR": "/data/output"
    }
)

Option 4: Docker env var debugging and Dockerfile best practices

# Dockerfile — make env vars available to all processes

# BAD: ENV only sets at image build time
# ENV API_KEY=hardcoded_value  # Never hardcode secrets

# GOOD: Declare expected env vars (no default = required at runtime)
ENV API_KEY=""
ENV DATABASE_URL=""
ENV LOG_LEVEL="INFO"

# GOOD: Pass build args separately from runtime env
ARG BUILD_VERSION=dev
ENV BUILD_VERSION=${BUILD_VERSION}

# GOOD: Entrypoint validates env before starting agent
COPY docker-entrypoint.sh /usr/local/bin/
RUN chmod +x /usr/local/bin/docker-entrypoint.sh
ENTRYPOINT ["docker-entrypoint.sh"]
CMD ["python3", "-m", "agent"]

#!/bin/bash
# docker-entrypoint.sh — validate env vars and export them

set -e

# Validate required env vars
required_vars=("API_KEY" "DATABASE_URL")
missing=()

for var in "${required_vars[@]}"; do
    if [[ -z "${!var}" ]]; then
        missing+=("$var")
    fi
done

if [[ ${#missing[@]} -gt 0 ]]; then
    echo "ERROR: Missing required environment variables: ${missing[*]}"
    echo "Pass them via: docker run -e API_KEY=... -e DATABASE_URL=..."
    exit 1
fi

# Export all vars so subprocesses inherit them
export API_KEY DATABASE_URL LOG_LEVEL

echo "Environment validated. Starting agent..."
exec "$@"

# docker-compose.yml — proper env var injection
services:
  agent:
    image: my-agent:latest
    environment:
      # Reference host env vars (must be set on host):
      API_KEY: ${API_KEY}
      DATABASE_URL: ${DATABASE_URL}
      # Set directly:
      LOG_LEVEL: INFO
      WORKER_TIMEOUT: "60"
    env_file:
      - .env.local   # Optional local overrides

Option 5: asyncio subprocess with environment

import asyncio
import os

async def run_async_subprocess(
    cmd: list[str],
    extra_env: dict[str, str] = None,
    timeout: float = 60.0
) -> tuple[str, str, int]:
    """
    Run subprocess asynchronously with inherited + extra environment.
    Returns (stdout, stderr, returncode).
    """
    env = {**os.environ}
    if extra_env:
        env.update(extra_env)

    proc = await asyncio.create_subprocess_exec(
        *cmd,
        env=env,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE
    )

    try:
        stdout, stderr = await asyncio.wait_for(proc.communicate(), timeout=timeout)
    except asyncio.TimeoutError:
        proc.kill()
        await proc.wait()
        raise TimeoutError(f"Subprocess timed out after {timeout}s: {cmd}")

    return stdout.decode(), stderr.decode(), proc.returncode

async def run_worker(worker_id: int) -> dict:
    """Run worker subprocess with proper env inheritance"""
    stdout, stderr, code = await run_async_subprocess(
        cmd=["python3", "-m", "worker", f"--id={worker_id}"],
        extra_env={
            "WORKER_ID": str(worker_id),
            "PYTHONPATH": os.environ.get("PYTHONPATH", "")
        },
        timeout=120.0
    )

    if code != 0:
        raise RuntimeError(
            f"Worker {worker_id} failed (exit code {code}):\n"
            f"STDOUT: {stdout[:500]}\n"
            f"STDERR: {stderr[:500]}"
        )

    return {"worker_id": worker_id, "output": stdout}

Option 6: Debug missing env vars in subprocess

import subprocess
import os

def debug_subprocess_environment(cmd: list[str]) -> dict:
    """
    Run a subprocess that prints its own environment.
    Useful for diagnosing why a subprocess can't see expected vars.
    """
    env_dump = subprocess.run(
        ["python3", "-c", "import os, json; print(json.dumps(dict(os.environ)))"],
        capture_output=True,
        text=True,
        env={**os.environ}  # Explicit inheritance
    )

    if env_dump.returncode != 0:
        return {"error": env_dump.stderr}

    import json
    subprocess_env = json.loads(env_dump.stdout)

    # Compare with parent
    parent_only = {k for k in os.environ if k not in subprocess_env}
    subprocess_only = {k for k in subprocess_env if k not in os.environ}
    different_values = {
        k for k in os.environ
        if k in subprocess_env and os.environ[k] != subprocess_env[k]
    }

    report = {
        "parent_env_count": len(os.environ),
        "subprocess_env_count": len(subprocess_env),
        "missing_in_subprocess": list(parent_only),
        "extra_in_subprocess": list(subprocess_only),
        "different_values": list(different_values),
    }

    if parent_only:
        print(f"WARNING: These vars are NOT inherited by subprocess: {parent_only}")
    if different_values:
        print(f"WARNING: These vars have different values in subprocess: {different_values}")

    return report

# Run this to diagnose env inheritance issues:
report = debug_subprocess_environment(["python3", "worker.py"])
print(f"Missing in subprocess: {report['missing_in_subprocess']}")

Subprocess Environment Inheritance Rules

Launch Method	Inherits Parent Env?	Notes
subprocess.run(cmd)	Yes	Default — inherits os.environ at launch time
subprocess.run(cmd, env={})	No	Empty env — explicit empty dict replaces all
subprocess.run(cmd, env={**os.environ, "K": "V"})	Yes + extras	Correct pattern
os.system(cmd)	Yes	Shell inherits env, but avoid — no output capture
os.execve(cmd, args, env)	Explicit only	Must pass env explicitly — replaces process
Docker CMD	Yes	Inherits from docker run -e / Dockerfile ENV
Docker exec into container	Yes	Same env as container
su - user in container	No	Login shell resets env — use su -m or sudo -E

Expected Token Savings

Subprocess fails → agent retries with debug → long investigation loop: ~15,000 tokens Proper env inheritance → subprocess runs first time: 0 debugging overhead

Environment

• Any agent that spawns subprocesses, shell scripts, or child processes; critical for agents running code execution tools, build systems, or multi-process pipelines
• Source: direct experience; subprocess environment issues are the most common cause of “works on my machine” failures when agents are containerized

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