Unable to execute Bash inside Docker Container

September 2, 2024

I am trying to execute a Bash file upon the start of the Container but it seems to not working as expected.

Below are the files involved (to keep things simpler i have simplfied the bash file)

Dockerfile :

FROM python:3.9-slim

# Create a working directory
WORKDIR /app

# Copy requirements
COPY requirements.txt app/


# Install tmux for the container 
RUN apt-get update && \
    apt-get install -y tmux && \
    apt-get clean

# Install requirements
RUN pip install --no-cache-dir -r app/requirements.txt

# Copy all files into the container's app directory
COPY . /app/

# # Make the .sh file executable
RUN chmod +x /app/start.sh

CMD ["/app/start.sh"]

start.sh :


#!/bin/bash

# Simple program to output a text into a txt file
OUTPUT_FILE="text.txt"

TEXT="Hello, this is a sample text written to text.txt."

echo "$TEXT" > "$OUTPUT_FILE"

Docker CLI used:

Buid: Docker build -t image_name .

Running in interactive mode : Docker run -it image_name /bin/bash

once i am inside the container, i tried to locate the text.txt file in /app dir which is supposed to be generated upon the start of the container but it was not there then i manually ran the start.sh and it worked perfectly fine.

>Solution :

The issue occurs because when you run the container interactively with docker run -it image_name /bin/bash, it overrides the default CMD directive (/app/start.sh) and instead of running your start.sh script, the container starts with /bin/bash as the entry point.

To fix it, run the container normally using: