Error burning custom system through ubuntu 19.04 live environment

I made a live environment for ubuntu19.04 on a U disk, and then I entered the live environment, executed Burning.sh, and burned grub.cfg, bzImage, roootfs.tar.gz from another U disk to the hard drive /dev/sda. Why did I restart my computer and enter the efi shell through the following actions?

Complete Burning.sh

 #!/usr/bin/bash

######################################################################
#      Author: madship_xk
######################################################################

current_path=$(pwd)
#root_path=/tmp/newOS
root_path=/mnt
boot_path=${root_path}/boot
grub_path=${boot_path}/grub
#clear
    
execute_command() {
    local command=$1
    eval "$command"
    local status=$?
    if [ $status -eq 0 ]; then
        echo "run the cmd:$command success"
    else
        echo "failed to run the cmd:$command" 
        exit 1
    fi
}



foo(){
    sudo mkdir -p ${root_path}
    #clear

    ls /dev/sda > ./tmp.txt
    hdstr=`awk 'NR==1 {print}' ./tmp.txt`
    echo "hdstr="${hdstr}
    rm ./tmp.txt

    echo "**************************************************************************"
    echo "**********            1st Command: FDISK                       ***********"
    echo "**********         Plese Follow the Introduction!              ***********"
    echo "**************************************************************************"

    sudo fdisk ${hdstr} <<EOT 1>/dev/null 2>/dev/null || exit 1
    d
    1
    d
    2
    d
    3
    d
    4

    n
    1
    34
    +8G
    n
    2
    

    w
EOT
    echo ""
    echo "**************************************************************************"
    echo "**********            2nd Command: PARTX                       ***********"
    echo "**********       Please Follow the Introduction!               ***********"
    echo "**************************************************************************"


    execute_command "sudo partx ${hdstr} 1>/dev/null"
    execute_command "sudo parted ${hdstr} set 1 boot off"
    execute_command "sudo parted ${hdstr} set 1 bios_grub on"
    sleep 1

    #clear
    echo "**************************************************************************"
    echo "**********         3rd Command: FORMAT SDA1                    ***********"
    echo "**********       Please Follow the Introduction!               ***********"
    echo "**************************************************************************"

    hdstr1=`printf "%s1" ${hdstr}`
    echo ${hdstr1}
    sleep 5
    execute_command "sudo /sbin/mkfs.ext4 ${hdstr1} 1>/dev/null"
    sleep 1

    #clear
    echo "**************************************************************************"
    echo "**********        4th Command: FORMAT SDA2                     ***********"
    echo "**********       Please Follow the Introduction!               ***********"
    echo "**************************************************************************"

    hdstr2=`printf "%s2" ${hdstr}`
    echo ${hdstr2}
    sleep 5
    execute_command "sudo /sbin/mkfs.ext4 ${hdstr2} 1>/dev/null"
    sleep 1


    #clear
    echo " "
    echo "**************************************************************************"                                                            
    echo "**********         5th Command: MIRROR IMAGE FOR SDA1          ***********"                                       
    echo "**********         Please Follow the Introduction!             ***********"                                                                
    echo "**************************************************************************"


    execute_command "sudo mkdir ${boot_path} -p"

    echo ${hdstr1}
    execute_command "sudo mount ${hdstr1} ${boot_path} 1>/dev/null"
    sleep 5

    execute_command "sudo mkdir -p ${grub_path}"
    echo "*********************Generate grub.cfg***************************************"
    execute_command "sudo cp ${current_path}/grub.cfg ${grub_path}/grub.cfg"
#   sudo cat > ${grub_path}/grub.cfg <<EOF 1>/dev/null || exit 1    
#   #Begin cfg
#   set default=0
#   set timeout=5

#   set root=(hd0,1)

#   menuentry "GNU/Linux, Test-6.4.0-rt" {
#       linux /bzImage rw root=/dev/sda2
#   }
# EOF
    execute_command "sudo grub-install --target=i386-pc --root-directory=${root_path} --boot-directory=${boot_path} ${hdstr} --force --recheck"
    execute_command "sudo chroot ${boot_path}"
    execute_command "sudo update-grub2 ${hdstr}"
    execute_command "sudo umount ${boot_path}"

    sleep 1

    #clear
    echo "**************************************************************************"
    echo "**********         6th Command: MIRROR IMAGE FOR SDB2          ***********"                                                                 
    echo "**********          Please Follow the Introduction!            ***********"                                       
    echo "**************************************************************************"                               


    sleep 2
    execute_command "sudo mount ${hdstr2} ${root_path}"
    execute_command "sudo cp \"${current_path}/bzImage\" ${root_path}"
    execute_command "sudo cp \"${current_path}/rootfs.tar.gz\" ${root_path}"
    cd ${root_path}
    execute_command "sudo tar -vxf rootfs.tar.gz"
    execute_command "echo \"y\" | sudo rm rootfs.tar.gz"
    cd ~
    execute_command "sudo umount ${root_path}"

    execute_command "sync"      
}

jumpa(){
    echo "Please input \"BURN\" to go to start point"
    read INP
    #echo $INP
    if [[ $INP = 'BURN' ]] ; then
        echo "Going to Start POINT......"
        sleep 2
        echo 
        foo
    else
        echo 
        jumpa
    fi
}

#jumpa
foo

grub.cfg:

#Begin cfg
set default=0
set timeout=4

set root=(hd0,1)

menuentry "GNU/Linux, Test-6.4.0-rt" {
    linux /bzImage rw root=/dev/sda2
}