unknown interface wlan0 after using wlan0

[sonettguy]

I'm struggling with the fragile nature of communicating with my headless pi zero w. (Running Rasbian Stretch.) When I take it out with me, like to my favorite coffee shop, it often connects to WiFi, then drops the signal within a half hour or so. To get it back, I run the following script in the background on boot.

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 1 #!/bin/bash
 2 sleep 5m
 3 while true ; do
 4         if ifconfig wlan0 | grep -q "inet addr:" ; then
 5                 sleep 5m
 6         else
 7                 echo "Network connection down. Attempting reconnection."
 8                 ifup --force wlan0
 9                 sleep 2m
10         fi
11 done

I see in two postings that some say ifup is obsolete. I have been using the Debian support documentation and saw nothing. Does it being obsolete mean that it is not working? When the script runs, it gives me the following error.

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pi@xx:/usr/bin $ bash net_mgr.sh
Network connection down. Attempting reconnection.
ifup: unknown interface wlan0
^C

So, I looked for wlan0 using ifconfig. Oh, well, its right there. I looked for it using ifquery. Oh, it's gone. What the heck?

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pi@xx:/usr/bin $ ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65xxx
        inet 127.x.x.x  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 2  bytes 230 (230.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2  bytes 230 (230.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

mon1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        unspec 00-DA-35-xx-xx-xx-xx-xx-00-00-00-00-00-00-00-00  txqueuelen 1000  (UNSPEC)
        RX packets 274822  bytes 58167822 (55.4 MiB)
        RX errors 0  dropped 3  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether b8:27:eb:xx:xx:xx  txqueuelen 1000  (Ethernet)
        RX packets 6459  bytes 916894 (895.4 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2147  bytes 325456 (317.8 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

pi@xx:/usr/bin $ ifquery -l
lo
wlan1
wlan2

pi@xx:/usr/bin $ ifconfig -v wlan0 up
SIOCSIFFLAGS: Operation not permitted
WARNING: at least one error occured. (-1)

So, I rebooted to get the internet connection back again. I went back to the terminal and tried "sudo ip link set wlan0 down" and I predictably lost the connection. I followed by typing "sudo ip link set wlan0 up." Nothing. It just goes back to prompt. It doesn't report an error nor does it give me the internet connection back.

I need some help in understanding why it appears I have wlan0 in some cases and not others. I need help to also understand why taking it down works, but bringing it up doesn't.

Here is the daemon.log for the first error reported in this post.

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Aug 21 09:59:10 pi systemd[1]: Started Session c2 of user pi.
Aug 21 10:22:05 pi systemd[1]: Reloading.
Aug 21 10:46:56 pi systemd[1]: Reloading.
Aug 21 11:09:53 pi dhcpcd[219]: wlan0: carrier lost
Aug 21 11:09:54 pi dhcpcd[219]: wlan0: deleting address fe80::fdaa:8445:xxxx:xxxx
Aug 21 11:09:54 pi avahi-daemon[236]: Withdrawing address record for fe80::fdaa:8445:xxxx:xxxx on wlan0.
Aug 21 11:09:54 pi avahi-daemon[236]: Leaving mDNS multicast group on interface wlan0.IPv6 with address fe80::fdaa:8445:xxxx:xxxx.
Aug 21 11:09:54 pi avahi-daemon[236]: Interface wlan0.IPv6 no longer relevant for mDNS.
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: deleting default route via 192.168.1.1
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: deleting route to 192.168.1.0/24
Aug 21 11:09:55 pi avahi-daemon[236]: Withdrawing address record for 192.168.x.x on wlan0.
Aug 21 11:09:55 pi avahi-daemon[236]: Leaving mDNS multicast group on interface wlan0.IPv4 with address 192.168.x.x.
Aug 21 11:09:55 pi avahi-daemon[236]: Interface wlan0.IPv4 no longer relevant for mDNS.
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: carrier acquired
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: IAID eb:0d:xx:xx
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: adding address fe80::fdaa:8445:xxxx:xxxx
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: probing address 192.168.x.x/24
Aug 21 11:09:55 pi dhcpcd[219]: wlan0: soliciting an IPv6 router
Aug 21 11:09:56 pi avahi-daemon[236]: Joining mDNS multicast group on interface wlan0.IPv6 with address fe80::fdaa:8445:xxxx:xxxx.
Aug 21 11:09:56 pi avahi-daemon[236]: New relevant interface wlan0.IPv6 for mDNS.
Aug 21 11:09:56 pi avahi-daemon[236]: Registering new address record for fe80::fdaa:8445:xxxx:xxxx on wlan0.*.
Aug 21 11:09:58 pi dhcpcd[18075]: sending commands to master dhcpcd process
Aug 21 11:09:58 pi dhcpcd[219]: control command: /sbin/dhcpcd -k wlan0
Aug 21 11:09:58 pi dhcpcd[219]: wlan0: removing interface
Aug 21 11:10:00 pi avahi-daemon[236]: Interface wlan0.IPv6 no longer relevant for mDNS.
Aug 21 11:10:00 pi avahi-daemon[236]: Leaving mDNS multicast group on interface wlan0.IPv6 with address fe80::fdaa:8445:xxxx:xxxx.
Aug 21 11:10:00 pi avahi-daemon[236]: Withdrawing address record for fe80::fdaa:8445:xxxx:xxxx on wlan0.

Since I take my pi out on the road with me, it would be nice if I had a way to get the terminal via bluetooth. I figured the app bluterm would be just what the doctor ordered, but dispite the fact that I can pair with my iPhone, I can't get any app, blueterm, yACK BLE or Bluefruit, to give me a terminal screen. Most don't connect at all. Any suggestions on this would be welcomed as well.

[sonettguy]

No suggestions in the case of the disappearing wlan0?