Summarize disk usage on Linux

cd /opt/mydir

du -sh *

du -sh * | sort -h

FILE_SERVER=/opt/my_file_server
# Need at least 17GB x 2
NEED_FREE=$((17224314*2))
FREE_SPACE=$(df -k --output=avail $FILE_SERVER | tail -1 | awk '{print $1}')

echo "INFO: Check if free space can not store more than 2 x 17GB"
if (( $FREE_SPACE < $NEED_FREE )); then
  	echo "INFO: Free sapce is not enough"
  	echo "INFO: Finding old directories which are stored more than 20 days"
        for old_dir in $( find $FILE_SERVER -maxdepth 1 -type d -name 'DIR_NAME*' -mtime +20 | sort ); do
            echo "Removing $old_dir"
            rm -rf $old_dir
        done
  else
  	echo "INFO: Free sapce is enough"
fi