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How To Enable Logging In Langflow

Introduction​

The Langflow API contains a endpoint for retrieving log messages. This endpoint requires log retrieval to be enabled in your Langflow application. For more information about the logging end point see https://docs.langflow.org/api-reference-api-examples#logs

This article assumes Langflow has been installed using procedure How To Install Langflow on Ubuntu Without Docker.

Component Code​

To test the logging we are going to use a simple component called Andrew1 that outputs the log message "Starting Andrew1".

from langflow.custom import Component
from langflow.io import MessageTextInput, Output
from langflow.schema.message import Message
import logging

class CombineTextComponent(Component):
    display_name = "Andrew1"
    description = "Concatenate two text sources into a single text chunk using a specified delimiter."
    icon = "merge"
    name = "CombineText"

    inputs = [
        MessageTextInput(
            name="text1",
            display_name="First Text",
            info="The first text input to concatenate.",
        )
    ]

    outputs = [
        Output(display_name="Combined Text", name="combined_text", method="combine_texts"),
    ]

    def combine_texts(self) -> Message:
        logger.info("Starting Andrew1")  # Log message here
        self.status = self.text1
        return self.text1

Enable Logging​

Step 1. Create the .env File​

Since Langflow is running as a systemd service, environment variables need to be stored in a .env file and loaded correctly. Navigate to Langflow’s working directory you can place the .env file here, or wherever Langflow is installed. In this example, we are going to place the file at /home/harry/.env.

Create or edit the .env file:

sudo nano /home/harry/.env

Add the following lines:

LANGFLOW_ENABLE_LOG_RETRIEVAL=true
LANGFLOW_LOG_RETRIEVER_BUFFER_SIZE=10000
LANGFLOW_LOG_LEVEL=DEBUG

Save and exit (CTRL+X, then Y, then ENTER).

Step 2. Update the Systemd Service File​

Modify the Langflow service file to load the .env file.

Open the service file:

sudo nano /etc/systemd/system/langflow.service

Update the [Service] section to load the .env file, note that the file contains an absolute path to the environment file:

[Unit]
Description=Langflow Service
After=network.target

[Service]
User=harry
EnvironmentFile=/home/harry/.env
ExecStart=/usr/bin/python3 -m langflow run --host 0.0.0.0 --port 8000
Restart=always

[Install]
WantedBy=multi-user.target
Save and exit (CTRL+X, then Y, then ENTER).

Step 3. Reload Systemd and Restart Langflow​

After modifying the service file, reload systemd and restart Langflow:

sudo systemctl daemon-reload
sudo systemctl restart langflow.service

Check if the service is running correctly:

sudo systemctl status langflow.service

Step 4. Verify Logs API​

Now, try the log retrieval API, this assumes that Langflow server ip address is 192.168.127.129, running on port 8000.

curl -X GET "http://192.168.127.129:8000/logs?lines_before=0&lines_after=0&timestamp=0" -H "accept: application/json"

The curl request should display the log messages from Langflow.

curl -X GET "http://192.168.127.129:8000/logs?lines_before=0&lines_after=0&timestamp=0" -H "accept: application/json"
{"1742721898813":"2025-03-23T09:24:58.813357+0000 DEBUG Building Prompt\n","1742721898818":"2025-03-23T09:24:58.818555+0000 DEBUG Building Chat Input\n","1742721898837":"2025-03-23T09:24:58.837079+0000 DEBUG Building OpenAI\n","1742721898877":"2025-03-23T09:24:58.877983+0000 DEBUG Logged transaction: c4bce45a-a560-4ec6-9f15-c075a83c5a15\n","1742721898896":"2025-03-23T09:24:58.896524+0000 DEBUG Logged transaction: 0f2c5da3-25c1-40f4-b11d-acd43d88bb64\n","1742721904746":"2025-03-23T09:25:04.746088+0000 DEBUG Building Andrew1\n","1742721904752":"2025-03-23T09:25:04.752512+0000 INFO Starting Andrew1\n","1742721904764":"2025-03-23T09:25:04.764104+0000 DEBUG Building Chat Output\n","1742721904783":"2025-03-23T09:25:04.783589+0000 DEBUG Logged transaction: 5e97f4d6-1e0e-4dd2-bfb4-cc3a902828bc\n","1742721904806":"2025-03-23T09:25:04.806003+0000 DEBUG Logged transaction: 31519031-5eb1-4b25-8ab3-4f400f237bb4\n"}

Clean Output​

The text output from the curl is a little difficult to read. The following python script outputs the logs in a json format.

import requests
import json

url = "http://192.168.127.129:8000/logs?lines_before=0&lines_after=0&timestamp=0"

headers = {"accept": "application/json"}

response = requests.get(url, headers=headers)

if response.status_code == 200:
    logs = response.json()
    print(json.dumps(logs, indent=4))
else:
    print("Failed to retrieve logs:", response.text)

Execute the python script

python.exe langflow-logs.py

Python script output

{
    "1742721898896": "2025-03-23T09:24:58.896524+0000 DEBUG Logged transaction: 0f2c5da3-25c1-40f4-b11d-acd43d88bb64\n",
    "1742721904746": "2025-03-23T09:25:04.746088+0000 DEBUG Building Andrew1\n",
    "1742721904752": "2025-03-23T09:25:04.752512+0000 INFO Starting Andrew1\n",
    "1742721904764": "2025-03-23T09:25:04.764104+0000 DEBUG Building Chat Output\n",
    "1742721904783": "2025-03-23T09:25:04.783589+0000 DEBUG Logged transaction: 5e97f4d6-1e0e-4dd2-bfb4-cc3a902828bc\n",
    "1742721904806": "2025-03-23T09:25:04.806003+0000 DEBUG Logged transaction: 31519031-5eb1-4b25-8ab3-4f400f237bb4\n",
    "1742721941158": "2025-03-23T09:25:41.158379+0000 DEBUG Job queue for job_id 46779e99-5636-49a0-91bc-d5638f1f228a marked for cleanup.\n",
    "1742721941165": "2025-03-23T09:25:41.165339+0000 INFO Commencing cleanup for job_id 46779e99-5636-49a0-91bc-d5638f1f228a\n",
    "1742721941170": "2025-03-23T09:25:41.170521+0000 DEBUG Removed 1 items from queue for job_id 46779e99-5636-49a0-91bc-d5638f1f228a\n",
    "1742721941175": "2025-03-23T09:25:41.175944+0000 INFO Cleanup successful for job_id 46779e99-5636-49a0-91bc-d5638f1f228a: resources have been released.\n"
}
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