kiss/contrib/kiss-chroot

#!/bin/sh
# Enter a kiss chroot

log() {
    printf '\033[32m->\033[m %s.\n' "$*"
}

die() {
    log "$*" >&2
    exit 1
}

run() {
    printf '%s\n' "$*"
    "$@" || return "${_ret:=0}"
}

clean() {
    log Unmounting host paths; {
        run umount "$1/dev/shm" 2>/dev/null
        run umount "$1/dev/pts"
        run umount "$1/dev"
        run umount "$1/proc"
        run umount "$1/run"
        run umount "$1/sys/firmware/efi/efivars" 2>/dev/null
        run umount "$1/sys"
        run umount "$1/tmp"
        run umount "$1/etc/resolv.conf"
    }
}

mounted() {
    # This is a pure shell mountpoint implementation. We're dealing
    # with basic (and fixed/known) input so this doesn't need to
    # handle more complex cases.
    [ -e "$1" ]         || return 1
    [ -e /proc/mounts ] || return 1

    while read -r _ target _; do
        [ "$target" = "$1" ] && return 0
    done < /proc/mounts

    return 1
}

mmount() {
    dest=$1
    shift
    mounted "$dest" || run mount "$@" "$dest"
}

main() {
    # Ensure input does not end in '/'.
    set -- "${1%"${1##*[!/]}"}"

    [ "$1" ]           || die Need a path to the chroot
    [ -d "$1" ]        || die Given path does not exist
    [ "$(id -u)" = 0 ] || die Script needs to be run as root

    # Intended behaviour.
    # shellcheck disable=SC2064
    trap "clean ${1%"${1##*[!/]}"}" EXIT INT

    log Mounting host paths; {
        mmount "$1/dev"     -o bind /dev
        mmount "$1/dev/pts" -o bind /dev/pts
        mmount "$1/dev/shm" -t tmpfs shmfs 2>/dev/null
        mmount "$1/proc"    -t proc  proc
        mmount "$1/run"     -t tmpfs tmpfs
        mmount "$1/sys"     -t sysfs sys
        mmount "$1/sys/firmware/efi/efivars" -t efivarfs efivarfs 2>/dev/null
        mmount "$1/tmp"     -o mode=1777,nosuid,nodev -t tmpfs tmpfs

        touch  "$1/etc/resolv.conf"
        mmount "$1/etc/resolv.conf" -o bind /etc/resolv.conf
    }

    log Entering chroot; {
        _ret=1

        run chroot "$1" /usr/bin/env -i \
            HOME=/root \
            TERM="$TERM" \
            SHELL=/bin/sh \
            USER=root \
            LOGNAME=root \
            CFLAGS="${CFLAGS:--march=x86-64 -mtune=generic -pipe -O2}" \
            CXXFLAGS="${CXXFLAGS:--march=x86-64 -mtune=generic -pipe -O2}" \
            MAKEFLAGS="${MAKEFLAGS:--j$(nproc 2>/dev/null || echo 1)}" \
            /bin/sh -l
    } || die chroot failed
}

main "$1"