Устанавливаем/обновляем systemrescuecd на флешке не затрагивая backstore:
#!/bin/sh
set -e
set -x
cd=/mnt/tmp
mount -o loop /usr/share/systemrescuecd/systemrescuecd-x86-newest.iso "$cd"
pmount "${1:?you forgot to specify the device name}"
cp -af "$cd"/* /mnt/"$1"
rm -rf /mnt/"$1"/syslinux
mv /mnt/"$1"/isolinux/isolinux.cfg /mnt/"$1"/isolinux/syslinux.cfg
sed -i -e 's/scandelay=1/scandelay=5/g' /mnt/"$1"/isolinux/syslinux.cfg
mv /mnt/"$1"/isolinux /mnt/"$1"/syslinux
pumount "$1"
(
cd "$cd"
./usb_inst.sh syslinux /dev/"$1"
sync
)
umount /mnt/tmp
sync
systemdrescuecd