create a loopback file and mount it

loopmount

#!/bin/bash
  
# sudo loopmount file size mount-point

touch $1
truncate -s $2 $1
mke2fs -t ext4 -F $1 1> /dev/null 2> /dev/null
if [[ ! -d $3 ]]; then
        echo $3 " not exist, creating..."
        mkdir $3
fi
mount $1 $3
df -h |grep $3