Run an "apt-get update" command in initContainers

Hi friends

I have a problem:
I tried run an initContainers for a ubuntu container.

  - name: setup-env
    image: busybox:latest
    command: ["sh", "-ce", "apt-get update"]

recieved error log:

sh: apt-get: not found

but I can run apt-get update in the container successfully.
I wonder why the error occured in initContainers.

Thank you!

The OS of container is as below

cat /etc/issue

Ubuntu 20.04.5 LTS \n \l

Your init container is using BusyBox which does not have apt-get