menhera.sh/menhera.sh

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#!/bin/bash
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set -Eeuo pipefail
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# config
WORKDIR="/tmp/menhera"
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ROOTFS="https://images.linuxcontainers.org/images/debian/stretch/amd64/default/20190409_05:24/rootfs.squashfs"
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# internal global variables
OLDROOT="/"
NEWROOT=""
# https://stackoverflow.com/a/3232082/2646069
confirm() {
# call with a prompt string or use a default
read -r -p "${1:-Are you sure? [y/N]} " response
case "$response" in
[yY][eE][sS]|[yY])
true
;;
*)
false
;;
esac
}
sync_filesystem() {
echo "Syncing..."
sync
sync
}
prepare_environment() {
echo "Loading kernel modules..."
modprobe overlay
modprobe squashfs
echo "Creating workspace in '${WORKDIR}'..."
# workspace
mkdir -p "${WORKDIR}"
mount -t tmpfs tmpfs "${WORKDIR}"
# new rootfs
mkdir -p "${WORKDIR}/newroot"
# readonly part of new rootfs
mkdir -p "${WORKDIR}/newrootro"
# writeable part of new rootfs
mkdir -p "${WORKDIR}/newrootrw"
# overlayfs workdir
mkdir -p "${WORKDIR}/overlayfs_workdir"
echo "Downloading temporary rootfs..."
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wget -c "${ROOTFS}" -O "${WORKDIR}/rootfs.squashfs"
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}
mount_new_rootfs() {
echo "Mounting temporary rootfs..."
mount -t squashfs "${WORKDIR}/rootfs.squashfs" "${WORKDIR}/newrootro"
mount -t overlay overlay -o rw,lowerdir="${WORKDIR}/newrootro",upperdir="${WORKDIR}/newrootrw",workdir="${WORKDIR}/overlayfs_workdir" "${WORKDIR}/newroot"
NEWROOT="${WORKDIR}/newroot"
}
install_software() {
echo "Installing OpenSSH Server into new rootfs..."
DEBIAN_FRONTEND=noninteractive chroot "${NEWROOT}" apt-get update -y
DEBIAN_FRONTEND=noninteractive chroot "${NEWROOT}" apt-get -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" install -y ssh
}
copy_config() {
echo "Copying important config into new rootfs..."
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! cp -ax "${OLDROOT}/etc/resolv.conf" "${NEWROOT}/etc"
! cp -axr "${OLDROOT}/etc/ssh" "${NEWROOT}/etc"
! cp -ax "${OLDROOT}/etc/"{passwd,shadow} "${NEWROOT}/etc"
! cp -axr "${OLDROOT}/root/.ssh" "${NEWROOT}/root"
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chroot "${NEWROOT}" chsh -s /bin/bash root
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cat > "${NEWROOT}/etc/motd" <<EOF
NOTICE
This is a minimal RAM system created by menhera.sh. Feel free to format your disk, but don't blame anyone
except yourself if you lost important files or your system is broken.
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Download menhera.sh at https://github.com/Jamesits/menhera.sh
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Have a lot of fun...
EOF
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}
swap_root() {
echo "Swapping rootfs..."
# prepare future mount point for our old rootfs
mkdir -p "${WORKDIR}/newroot/mnt/oldroot"
mount --make-rprivate /
# swap root
pivot_root "${WORKDIR}/newroot" "${WORKDIR}/newroot/mnt/oldroot"
OLDROOT="/mnt/oldroot"
NEWROOT="/"
# move mounts
for i in dev proc sys run; do mount --move "${OLDROOT}/$i" "${NEWROOT}/$i"; done
mount -t tmpfs tmpfs "${NEWROOT}/tmp"
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mkdir -p "${WORKDIR}"
mount --move "${OLDROOT}/${WORKDIR}" "${WORKDIR}"
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echo "Restarting SSH daemon..."
systemctl restart ssh
}
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clear_processes() {
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echo "Disabling swap..."
swapoff -a
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echo "Restarting systemd..."
systemctl daemon-reexec --no-block
sleep 15
echo "Killing all programs still using the old root..."
fuser -kvm "${OLDROOT}" -15
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# in most cases the parent process of this script will be killed, so goodbye
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}
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if [[ $EUID -ne 0 ]]; then
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echo "This script must be run as root"
exit 1
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fi
echo -e "We will start a temporary RAM system as your recovery environment."
echo -e "Note that this script will kill programs and umount filesystems without prompting."
echo -e "Please confirm:"
echo -e "\tYou have closed all programs you can, and backed up all important data"
echo -e "\tYou can SSH into your system as root user"
confirm || exit -1
sync_filesystem
prepare_environment
mount_new_rootfs
copy_config
install_software
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swap_root
echo -e "If you are connecting from SSH, please create a second session to this host and confirm you can get a shell."
echo -e "After your confirmation, we are going to kill the old SSH server."
confirm || exit -1
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clear_processes