Difference Docker USER vs linux su

Hi,

I am trying to deploy db2 image using docker.

I am using below command to start db2 engine from dockerfile.

RUN su - db2inst1-c "abc.sh"

#####abc.sh######
#!bin/bash
db2start
-------------------------------------------------------------------------------------
I am trying to modify the above command like below,

USER db2inst1
RUN abc.sh

Getting error message that db2start command not found..

Please help to fix this.

I have posted this question in docker forum, refer below url:
https://forums.docker.com/t/db2-image-db2start-failing-for-non-root-user/113542

Thanks.