yum-chroot.sh

yum-chroot.sh

#!/bin/bash

this_script=$(basename $0)

print_usage()
{
    echo <<EOF
Usage: ${this_script} create CHROOT_DIR [CENTOS_RELEASE_RPM_URL]
       ${this_script} run    CHROOT_DIR [COMMAND ...]
       ${this_script} --help

The first form of the command is used if CHROOT_DIR does not already exist or
is an empty directory. A new chroot will be created at CHROOT_DIR based upon
the centos-release RPM file pointed to by CENTOS_RELEASE_RPM_URL. After the
chroot is created, it will be entered using a bash login shell.

The second form of the command is used if CHROOT_DIR already exists and is not
empty. It will execute COMMAND inside the chroot. The default command is
'/bin/bash -l'
EOF
}

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

unmount_chroot()
{
    chroot=$(readlink -e $1) || return 1
    [[ ${chroot} == / ]] && return 1
    chroot_mounted_dirs=$(awk -v chroot="${chroot}" '$2 ~ chroot {print $2}' /proc/mounts) || return 1
    for mount_point in ${chroot_mounted_dirs}; do
        echo "Unmounting ${mount_point} ..."
        umount ${mount_point}
    done
}

dir_is_empty()
{
    [[ ! "$(find $1 -maxdepth 0 -empty)" == "" ]]
}

create_chroot()
{
(   set -e
    chroot_dir=$(readlink -m $1)
    centos_release_rpm=${2}
    if [[ ${centos_release_rpm} = *.x86_64.rpm ]]; then
        basearch=x86_64
        arch=x86_64
    else
        basearch=i386
        arch=i686
    fi
    case "$centos_release_rpm" in
        */6*/os/i386/*)
            basearch=i386
            arch=i686
            releasever=6
            ;;
        */6*/os/x86_64/*)
            basearch=x86_64
            arch=x86_64
            releasever=6
            ;;
        */7*/os/x86_64/*)
            basearch=x86_64
            arch=x86_64
            releasever=7
            ;;
        *)
            cat 1>&2 <<EOF
Unsupported RHEL release. Supported versions are:

  * 6/i386
  * 6/x86_64
  * 7/x86_64
EOF
            return 1
            ;;
    esac
    mkdir -p ${chroot_dir}
    if ! dir_is_empty ${chroot_dir}; then
        echo "${chroot_dir} is not empty."
        read -p "Proceed anyway? [yN] " proceed
        [[ $proceed = [yY] ]] || return 1
    fi
    rpm --root=${chroot_dir} --install --nodeps ${centos_release_rpm}
    mkdir -p ${chroot_dir}/etc/yum/vars
    echo ${releasever} > ${chroot_dir}/etc/yum/vars/releasever
    echo ${arch}       > ${chroot_dir}/etc/yum/vars/arch
    echo ${basearch}   > ${chroot_dir}/etc/yum/vars/basearch
    yum --installroot=${chroot_dir} --assumeyes --nogpgcheck install yum
    chroot ${chroot_dir} rpm --rebuilddb
)
}

run_chroot()
{
(   set -e
    chroot_dir=$(readlink -e $1)
    shift
    chroot_command="$@"
    if [ -z ${chroot_command} ]; then
        chroot_command="/bin/bash -l"
    fi
    echo "Setting up chroot and launching: ${chroot_command}"

    trap "unmount_chroot \"${chroot_dir}\"" EXIT

    # List of required bind mounts in order of dependency.
    bind_mount_points="/proc /dev"
    for mount_point in ${bind_mount_points}; do
        if [ -d ${mount_point} ] && ! mount | grep -q " on ${chroot_dir}${mount_point} "; then
            echo "Mounting ${chroot_dir}${mount_point} ..."
            mkdir -p ${chroot_dir}${mount_point}
            mount --bind ${mount_point} ${chroot_dir}${mount_point}
        fi
    done

    cp -p /etc/resolv.conf ${chroot_dir}/etc/
    touch ${chroot_dir}/root/.Xauthority
    
    # TODO: The following is used in lieu of bind-mounting /tmp /run and /dev/pts
    xauth extract - $DISPLAY | xauth -f ${chroot_dir}/root/.Xauthority merge -
    chroot ${chroot_dir} env XAUTHORITY=/root/.Xauthority ${chroot_command}

    echo "Exited chroot."
)
}

case "$1" in
    create)
        echo "Installing new chroot ..."
        release_url="$3"

        # Allow interactive selection if no URL provided
        if [ -z "${release_url}" ]; then
            url_choices='http://mirror.centos.org/centos/6/os/i386/Packages/centos-release-6-5.el6.centos.11.1.i686.rpm
http://mirror.centos.org/centos/6/os/x86_64/Packages/centos-release-6-5.el6.centos.11.1.x86_64.rpm
http://mirror.centos.org/centos/7/os/x86_64/Packages/centos-release-7-0.1406.el7.centos.2.3.x86_64.rpm'
            echo -e "Select RPM URL to initialize chroot:\n"
            echo "$url_choices" | awk '{ print "  [", NR, "]", $0 }'
            read -p "Selection: " choice
            release_url=$(echo "${url_choices}" | sed -n "${choice} p")
        fi
        
        create_chroot ${2} ${release_url} || die "Failed to create chroot"
        cat <<EOF
==============================================================================
New chroot created successfully. You can launch a bash session inside the
chroot with:

  sudo ${this_script} run

You may wish to install the util-linux package in order to have a more
complete environment for interactive use.
==============================================================================
EOF
        ;;
    
    run)
        shift
        run_chroot "$@" || dia "Failed to launch chroot"
        ;;
    
    -h|--help)
        print_usage
        exit 0
        ;;
    
    '')
        print_usage
        exit 1
        ;;
esac