kiss/contrib/kiss-chroot

#!/bin/sh -e
# Enter a kiss chroot

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

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

clean() {
    log Unmounting /dev, /proc and /sys from chroot; {
        umount "$1/sys/firmware/efi/efivars" 2>/dev/null ||:
        umount "$1/dev"  ||:
        umount "$1/proc" ||:
        umount "$1/sys"  ||:
    }

    log Cleaning leftover host files; {
        rm -f "$1/root/.ash_history"
        rm -f "$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
}

[ -z "$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

trap 'clean "$1"' EXIT INT

log Mounting /dev, /proc and /sys from host; {
    mounted "$1/dev"  || mount -o bind /dev "$1/dev"  ||:
    mounted "$1/proc" || mount -t proc proc "$1/proc" ||:
    mounted "$1/sys"  || mount -t sysfs sys "$1/sys"  ||:

    mounted "$1/sys/firmware/efi/efivars" ||
        mount -t efivarfs efivarfs "$1/sys/firmware/efi/efivars" 2>/dev/null ||:
}

log Copying /etc/resolv.conf from host; {
    cp -f /etc/resolv.conf "$1/etc" ||:
}

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