gunicorn logs: where they go, access log, error log (tested)

By default gunicorn writes its error log (including 500 tracebacks) to stderr and writes no access log at all. Add --access-logfile - to log requests to stdout, --error-logfile path to write errors to a file, and --capture-output to send print() output from your app there too.

1. Where each kind of output goes

app.py prints, logs a warning, and raises on /boom:

import logging, sys
log = logging.getLogger("myapp")

def app(environ, start_response):
    print("print() from the app")
    log.warning("logger.warning from the app")
    if environ["PATH_INFO"] == "/boom":
        raise ValueError("boom")
    start_response("200 OK", [("Content-Type", "text/plain")])
    return [b"ok\n"]

run.py starts gunicorn three ways, requests / and /boom, and shows the terminal output and log files (startup lines filtered out):

import os, subprocess, time, urllib.request
G = "/tmp/fx384/ve/bin/gunicorn"
def trial(args):
    for f in ("error.log", "access.log"):
        if os.path.exists(f): os.remove(f)
    cmd = [G, "-b", "127.0.0.1:8966", *args, "app:app"]
    print("$ gunicorn", " ".join(cmd[1:]))
    p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)
    time.sleep(1.5)
    for path in ("/", "/boom"):
        try: urllib.request.urlopen(f"http://127.0.0.1:8966{path}", timeout=10)
        except Exception as ex: print(f"  (GET {path} -> {ex})")
    time.sleep(0.5); p.terminate(); out = p.communicate()[0]
    print("  --- terminal ---")
    for line in out.splitlines():
        if any(k in line for k in ("Starting gunicorn", "Listening", "Using worker", "Booting", "Control socket", "Handling signal", "Worker exiting", "Shutting down", "  File", "    ")): continue
        print("  " + line)
    for f in ("error.log", "access.log"):
        if os.path.exists(f):
            print(f"  --- {f} (grep app/GET/Error) ---")
            for line in open(f):
                if any(k in line for k in ("app", "GET", "Error", "boom")): print("  " + line.rstrip())
    print()
trial([])
trial(["--access-logfile", "-"])
trial(["--access-logfile", "access.log", "--error-logfile", "error.log", "--capture-output"])

Output (gunicorn 26.2.0, Python 3.13.5, Linux):

$ gunicorn -b 127.0.0.1:8966 app:app
  (GET /boom -> HTTP Error 500: Internal Server Error)
  --- terminal ---
  print() from the app
  logger.warning from the app
  print() from the app
  logger.warning from the app
  [2026-10-23 20:34:21 +0100] [3408698] [ERROR] Error handling request GET /boom
  Traceback (most recent call last):
  ValueError: boom

$ gunicorn -b 127.0.0.1:8966 --access-logfile - app:app
  (GET /boom -> HTTP Error 500: Internal Server Error)
  --- terminal ---
  print() from the app
  logger.warning from the app
  127.0.0.1 - - [23/Oct/2026:20:34:24 +0100] "GET / HTTP/1.1" 200 3 "-" "Python-urllib/3.13"
  print() from the app
  logger.warning from the app
  [2026-10-23 20:34:24 +0100] [3408701] [ERROR] Error handling request GET /boom
  Traceback (most recent call last):
  ValueError: boom
  127.0.0.1 - - [23/Oct/2026:20:34:24 +0100] "GET /boom HTTP/1.1" 500 0 "-" "-"

$ gunicorn -b 127.0.0.1:8966 --access-logfile access.log --error-logfile error.log --capture-output app:app
  (GET /boom -> HTTP Error 500: Internal Server Error)
  --- terminal ---
  --- error.log (grep app/GET/Error) ---
  print() from the app
  logger.warning from the app
  print() from the app
  logger.warning from the app
  [2026-10-23 20:34:26 +0100] [3408704] [ERROR] Error handling request GET /boom
    File "/tmp/gl405/app.py", line 8, in app
      raise ValueError("boom")
  ValueError: boom
  --- access.log (grep app/GET/Error) ---
  127.0.0.1 - - [23/Oct/2026:20:34:26 +0100] "GET / HTTP/1.1" 200 3 "-" "Python-urllib/3.13"
  127.0.0.1 - - [23/Oct/2026:20:34:26 +0100] "GET /boom HTTP/1.1" 500 0 "-" "-"

2. What this shows

• Default: the error log goes to stderr (your terminal, or journalctl -u yourservice under systemd, or docker logs in a container). The 500 traceback ([ERROR] Error handling request GET /boom) is there. There is no access log: the two GET requests left no line.
• --access-logfile - turns the access log on and sends it to stdout: one line per request with status (200, 500).
• --error-logfile error.log --access-logfile access.log --capture-output sends everything to files and nothing to the terminal; --capture-output is what put the app's print() and logger output into error.log.
• A 500 from an unhandled exception is logged at [ERROR] with the full traceback, and the frame in your code (app.py, line 8) shows the cause.

In gunicorn.conf.py the same settings are accesslog = "-", errorlog = "error.log", capture_output = True.

Related: gunicorn access log format examples, gunicorn 500 Internal Server Error, gunicorn unrecognized arguments, gunicorn [CRITICAL] WORKER TIMEOUT.

Written with AI assistance. Measured on 2026-10-23 with gunicorn 26.2.0 and Python 3.13.5 on Linux. The script ran verbatim and the output was pasted unedited. PlainHeaders is our extension; gunicorn is free.