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=""
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# internal global variables
OLDROOT="/"
NEWROOT=""
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# fix possible PATH problems
export PATH="$PATH:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
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# environment compatibility
__compat_restart_ssh() {
if [ -x "$(command -v systemctl)" ]; then
systemctl daemon-reload
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systemctl restart ssh
elif [ -x "$(command -v service)" ]; then
service ssh restart
else
echo "ERROR: Cannot restart SSH server" >&2
exit 1
fi
}
__compat_reload_init() {
if [ -x "$(command -v systemctl)" ]; then
systemctl daemon-reexec
elif [ -x "$(command -v telinit)" ]; then
telinit u
else
echo "ERROR: Cannot re-exec init" >&2
exit 1
fi
}
# helper functions
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# https://stackoverflow.com/a/3232082/2646069
confirm() {
# call with a prompt string or use a default
read -r -p "${1:-Are you sure? [y/N]} " response
case "$response" in
[yY][eE][sS]|[yY])
true
;;
*)
false
;;
esac
}
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# jobs
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get_rootfs() {
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if [ -n ${ROOTFS} ]; then
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echo "Getting rootfs URL..."
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# forgive me for parsing HTML with these shit
# and hope it works
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ROOTFS_TIME=$(curl -fsSL "https://images.linuxcontainers.org/images/debian/stretch/amd64/default/?C=M;O=D" | grep -oP '(\d{8}_\d{2}:\d{2})' | head -n 1)
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ROOTFS="https://images.linuxcontainers.org/images/debian/stretch/amd64/default/${ROOTFS_TIME}/rootfs.squashfs"
else
echo "\$ROOTFS is set to '$ROOTFS'"
fi
}
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sync_filesystem() {
echo "Syncing..."
sync
sync
}
prepare_environment() {
echo "Loading kernel modules..."
modprobe overlay
modprobe squashfs
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sysctl kernel.panic=10
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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 "${WORKDIR}/overlayfs_workdir"
echo "Downloading temporary rootfs..."
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curl -L -C - -o "${WORKDIR}/rootfs.squashfs" "${ROOTFS}"
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}
mount_new_rootfs() {
echo "Mounting temporary rootfs..."
mount -t squashfs "${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..."
# disable APT cache
echo -e 'Dir::Cache "";\nDir::Cache::archives "";' > "${NEWROOT}/etc/apt/apt.conf.d/00_disable-cache-directories"
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DEBIAN_FRONTEND=noninteractive chroot "${NEWROOT}" apt-get update -y
DEBIAN_FRONTEND=noninteractive chroot "${NEWROOT}" apt-get -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" install -y openssh-server
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}
copy_config() {
echo "Copying important config into new rootfs..."
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! cp -ax "${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 > "${NEWROOT}/etc/motd" <<EOF
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Download menhera.sh at https://github.com/Jamesits/menhera.sh
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!!!NOTICE!!!
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This is a minimal RAM system created by menhera.sh. Feel free to format your disk, but don't blame anyone
except yourself if you lost important files or your system is broken.
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If you think you've done something wrong, reboot immediately -- there is still hope.
Your original rootfs is at /mnt/oldroot. Be careful dealing with it.
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Have a lot of fun...
EOF
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}
swap_root() {
echo "Swapping rootfs..."
# prepare future mount point for our old rootfs
mkdir -p "${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}" "${WORKDIR}"
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echo "Restarting SSH daemon..."
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__compat_restart_ssh
}
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clear_processes() {
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echo "Disabling swap..."
swapoff -a
echo "Restarting init process..."
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__compat_reload_init
# hope 15s is enough
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sleep 15
echo "Killing all programs still using the old root..."
fuser -kvm "${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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# main procedure
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LIBRARY_ONLY=0
while test $# -gt 0
do
case "$1" in
--lib) LIBRARY_ONLY=1
;;
esac
shift
done
if [[ $LIBRARY_ONLY -eq 1 ]]; then
# acting as a library only
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return 0
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fi
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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
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get_rootfs
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sync_filesystem
prepare_environment
mount_new_rootfs
copy_config
install_software
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swap_root
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echo -e "If you are connecting from SSH, please create a second session to this host use root and"
echo -e "confirm you can get a shell."
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echo -e "After your confirmation, we are going to kill the old SSH server."
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if confirm; then
clear_processes
else
echo -e "Please manually issue a reboot to recover your old OS. If you believe there is a bug in menhera.sh, "
echo -e "raise a ticket at https://github.com/Jamesits/menhera.sh/issues ."
exit 1
fi