Script made to update Ubuntu Netboot for PXE Server

update_ubuntu_netboot.sh

#!/usr/bin/env bash
# crontab -e
# 0 3 * * * /bin/bash /root/update_ubuntu_netboot.sh
# apt install syslinux-common
#=============================================
ubuntu_files='/srv/tftp/images/ubuntu'
iso_location='/srv/tftp/images/ISO'
dist=("focal" "jammy")
# focal 20.04
# jammy 22.04

mkdir -p /mnt/iso

cd /tmp

for str in ${dist[@]}; do
  mkdir -p $ubuntu_files/$str
  wget -q http://releases.ubuntu.com/$str/SHA256SUMS -O SHA256SUMS-$str
  iso_filename=$(grep -F "server" SHA256SUMS-$str | cut -d '*' -f 2)
  if test -f "$ubuntu_files/$str/current"; then
    iso_previous=$(cat $ubuntu_files/$str/current)
  else
    echo "$iso_filename" > $ubuntu_files/$str/current
    iso_previous="none"
  fi

  if [[ $iso_previous == $iso_filename ]]; then
    echo -e "$str\t: Same ISO name, don't download"
    rm -rf SHA256SUMS-$str
  else
    echo "$iso_filename" > $ubuntu_files/$str/current
    iso_sha256=$(grep -F "server" SHA256SUMS-$str | cut -d ' ' -f 1)
    echo -e "\n\tDownloading $str ISO..."
    wget -q http://releases.ubuntu.com/$str/$iso_filename -O ubuntu.iso
    chksum=$(sha256sum ubuntu.iso)
    chksum_array=($chksum)
    chksum=${chksum_array[0]}
    #echo "checksum1 = $iso_sha256"
    #echo "checksum2 = $chksum"
    if [[ $chksum == $iso_sha256 ]]; then
      echo -e "\t Checksum OK"
      mount ubuntu.iso /mnt/iso
      echo "Copying files..."
      cp -f /mnt/iso/casper/{vmlinuz,initrd} $ubuntu_files/$str/
      umount /mnt/iso
      mv ubuntu.iso $iso_location/ubuntu-$str.iso
      if test -f "$ubuntu_files/$str/ldlinux.c32"; then
        echo "ldlinux.c32 already present in $str directory"
      else
        cp /usr/lib/syslinux/modules/bios/ldlinux.c32 $ubuntu_files/$str/
      fi
      rm -rf SHA256SUMS-$str
    else
      echo "Checksum  mismatch - nothing done."
    fi
  fi
done
echo "End."
exit 0