DEV Community

Akshay Gore
Akshay Gore

Posted on

Dockerfile: CMD vs ENTRYPOINT

#docker #containers #cmd #shell

CMD and ENTRYPOINT commands in Dockerfile can get confusing if not tried by actually executing it.

Show, don't tell

1. CMD

  • By default docker images like ubuntu have CMD as last command in its dockerfile as below:
    CMD ["/bin/bash"]

  • When we run docker container with below commands

docker run --rm --name cmd ubuntu:latest ls /home

or

docker run --rm --name cmd ubuntu:latest date

Default command gets overridden by what we pass as arguments, in this cases as "ls /home" and "date"

  • Above docker runs produces below outputs respectively: 
~  % docker run --rm --name cmd ubuntu:latest ls -l /home/ubuntu
total 0
Enter fullscreen mode Exit fullscreen mode 
~  % docker run --rm --name cmd ubuntu:latest date
Sat Dec 13 16:22:53 UTC 2025
Enter fullscreen mode Exit fullscreen mode

2. ENTRYPOINT

  • Let's create a docker image (entrypoint:1.0.0) with ENTRYPOINT command 
FROM ubuntu:latest
WORKDIR /app
COPY script.sh .
RUN ["chmod","+x","script.sh"]
ENTRYPOINT ["/app/script.sh"]
CMD ["world"]
Enter fullscreen mode Exit fullscreen mode

script.sh

#!/bin/bash
echo "Hello $1"
Enter fullscreen mode Exit fullscreen mode
  • Above script expects a single argument
  • If we don't pass any argument, the default argument will be the one provided in CMD 
% docker run --rm --name entrypoint entrypoint:1.0.0
Hello world
Enter fullscreen mode Exit fullscreen mode
  1. If we pass an argument during a docker run then 
% docker run --rm --name entrypoint entrypoint:1.0.0 december
Hello december
Enter fullscreen mode Exit fullscreen mode

Learnings:

  • We can always override the CMD
  • We cannot override ENTRYPOINT, but we can override the arguments passed to the ENTRYPOINT using CMD as last command during image creation
  • ENTRYPOINT or CMD depends on usecase

Top comments (0)