The solution to the Python script running normally but nohup error

1. Introduction

When deploying Python applications on Linux servers, we often use the nohup command to make the program run in the background. However, sometimes there is no problem running python directly, but an error is reported when running using nohup, for example:

nohup: ignoring input and redirecting stderr to stdout
  File "", line 28
(f"Received Cookie {cookie}")
                              ^
SyntaxError: invalid syntax

This error is usually caused by incompatible with f-string (formatted string literals). This article will analyze the causes of this problem in depth and provide multiple solutions, while comparing similar scenarios in Java.

2. Problem analysis

2.1 What is f-string

f-string (formatted string literals) is a string formatting method introduced in Python 3.6, which is simpler than the traditional % and .format():

name = "Alice"
age = 25
print(f"Name: {name}, Age: {age}")  # Python 3.6+

2.2 Why is there no problem to run directly? Nohup runs error

When running directly, you may use python3 or python3.6+ interpreter.

When nohup runs, python2 may be called by default, and Python does not support f-string.

2.3 Performance of similar problems in Java

In Java, different JDK versions can also lead to syntax incompatibility. For example:

try-with-resources（Java 7+）：

try (BufferedReader br = new BufferedReader(new FileReader(""))) {
    // Java 7+ support}

Running on Java 6 will result in an error.

var keyword (Java 10+):

var list = new ArrayList<String>(); // Java 10+

Running on Java 8 will result in an error.

3. Solution

3.1 Confirm the Python version

python --version      # Probably Pythonpython3 --version     # Check Python version

3.2 Using the correct Python interpreter

nohup python3  >  2>&1 &

Or specify the full path:

nohup /usr/bin/python3  >  2>&1 &

3.3 Using a virtual environment (recommended)

python3 -m venv venv       # Create a virtual environmentsource venv/bin/activate   # Activate the environmentnohup venv/bin/python  >  2>&1 &

3.4 Downgrade code compatibility (not recommended)

If you have to use Python, you can modify the code:

# Python Compatible Writing("ReceivedCookie {}".format(cookie))
# or("Cookie received %s" % cookie)

3.5 Specifying the interpreter using Shebang

Add on the first line:

#!/usr/bin/env python3

Then give execution permissions:

chmod +x 
nohup ./ >  2>&1 &

4. In-depth discussion: Why nohup calls different Python

4.1 Shell's default Python

nohup uses /usr/bin/python by default, while some Linux systems (such as CentOS 7) link to python2 by default.

4.2 Impact of environmental variables

PATH environment variables may affect the selection of the interpreter:

echo $PATH  # View Python pathwhich python
which python3

4.3 Comparing Java environment variable issues

In Java, JAVA_HOME and PATH also affect the version:

export JAVA_HOME=/usr/lib/jvm/java-11-openjdk  # Specify JDK 11export PATH=$JAVA_HOME/bin:$PATH

5. Best Practices

5.1 Using Virtual Environment (Python)

python3 -m venv venv
source venv/bin/activate
pip install -r 
nohup venv/bin/python  >  2>&1 &

5.2 Using Docker (cross-version compatible)

FROM python:3.8
COPY . /app
WORKDIR /app
RUN pip install -r 
CMD ["python", ""]

run:

docker build -t myapp .
docker run -d myapp

5.3 Similar practices in Java

Maven specifies the JDK version:

<properties>
    <>11</>
    <>11</>
</properties>

Docker runs Java:

FROM openjdk:11
COPY target/ /
CMD ["java", "-jar", "/"]

6. Summary

Key points:

• Always clarify the Python/Java version to avoid syntax incompatibility.
• Use virtual environment or Docker to ensure the consistency of the environment.
• Log redirection: nohup ... > log 2>&1 &.

7. Appendix

Python version detection script

import sys
print("Python version:", )

Java version detection

public class JavaVersion {
    public static void main(String[] args) {
        ("Java version: " + (""));
    }
}

Through this article, you should be able to solve the problem of nohup running Python script errors and understand the importance of compatibility of different language versions.

This is the article about the solution to the Python script running normally but nohup errors reported. For more related Python nohup errors, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!