change docker default root directory /var/lib/docker

[root@db-172-16-3-221 docker]# vi /etc/init.d/docker 
start() {
    [ -x $exec ] || exit 5

    if ! [ -f $pidfile ]; then
        prestart
        printf "Starting $prog:\t"
        echo "\n$(date)\n" >> $logfile
# 改这行如下, 以/data01/docker作为root : 
        $exec -d -g /data01/docker &>> $logfile &
        pid=$!
        touch $lockfile
        # wait up to 10 seconds for the pidfile to exist.  see
        # https://github.com/dotcloud/docker/issues/5359
        tries=0
        while [ ! -f $pidfile -a $tries -lt 10 ]; do
            sleep 1
            tries=$((tries + 1))
        done
        success
        echo
    else
        failure
        echo
        printf "$pidfile still exists...\n"
        exit 7
    fi
}