Raspberry 3B+ Wi-Fi in access point mode

I have installed the latest Raspbian Light on my new Raspberry 3B+ then followed the tutorial here:

https://www.raspberrypi.org/documentation/configuration/wireless/access-point.md

My system is:

$ uname -a
Linux raspberrypi 4.14.79-v7+ #1159 SMP Sun Nov 4 17:50:20 GMT 2018 armv7l GNU/Linux

After completed the procedure, I cannot see any SSID NameOfNetwork with an external device. wlan0 seems not active:

wlan0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether b8:27:eb:d5:30:24  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

And it seems wlan0 does not exist:

sudo ifup wlan0
ifup: unknown interface wlan0

To summarize what I did:

1. Add static IP for wlan0 in /etc/dhcpd.conf
2. Configure a DHCP server on wlan0 in /etc/dnsmasq.conf
3. COnfigure hostapd in /etc/hostapd/hostapd.conf
4. Bind hostapd in /etc/default/hostapd
5. Start the services hostapd, dnsmasq

It seems WPA supplicant is inactive at this point:

sudo systemctl status wpa_supplicant.service
● wpa_supplicant.service - WPA supplicant
   Loaded: loaded (/lib/systemd/system/wpa_supplicant.service; disabled; vendor preset: enabled)
   Active: inactive (dead)

So I started it:

sudo systemctl status wpa_supplicant.service

But still, my Wi-Fi is not yet working

I tried to start wpa_supplicant manually:

 sudo wpa_supplicant -B -iwlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf
Successfully initialized wpa_supplicant
ctrl_iface exists and seems to be in use - cannot override it
Delete '/var/run/wpa_supplicant/wlan0' manually if it is not used anymore
Failed to initialize control interface 'DIR=/var/run/wpa_supplicant GROUP=netdev'.
You may have another wpa_supplicant process already running or the file was
left by an unclean termination of wpa_supplicant in which case you will need
to manually remove this file before starting wpa_supplicant again.

nl80211: deinit ifname=wlan0 disabled_11b_rates=0

Then the configuration of the wireless device

iwconfig
eth0      no wireless extensions.

lo        no wireless extensions.

wlan0     IEEE 802.11  ESSID:off/any
          Mode:Managed  Access Point: Not-Associated   Tx-Power=31 dBm
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:on

What should I do?