sudo sed -i '/^ui / d' /tmp/custom/newiso/isolinux/isolinux.cfg   # disable gfxboot
sudo sed -i 's/quiet splash/quiet splash persistent/' /tmp/custom/newiso/isolinux/txt.cfg /tmp/custom/newiso/boot/grub/grub.cfg

# make persistent usb
# sudo fdisk /dev/sdb  # n <enter> <enter> <enter> <enter> w
sudo mkfs.vfat /dev/sdb1
sudo mkfs.ext4 -L casper-rw -O ^has_journal /dev/sdb2

sudo mount /dev/sdb1 /mnt
sudo rsync -av /tmp/custom/newiso/ /mnt
sudo mv /tmp/custom/newiso/isolinux /tmp/custom/newiso/syslinux
sudo mv /tmp/custom/newiso/syslinux/isolinux.cfg /tmp/custom/newiso/syslinux/syslinux.cfg
sudo syslinux -d syslinux /dev/sdb1
sudo umount /mnt
sudo dd if=/usr/lib/syslinux/bios/mbr.bin of=/dev/sdb