The 8812 driver included in the kernel is the Realtek version, you’re going to need to install the realtek dkms version to get monitor/injection support.

Sorry, my bad. I had installed the realtek-rtl88xxau-dkms but forgot to include it in the steps to duplicate the problem. Here is the console output created during the driver install:

root@kali:~# apt install realtek-rtl88xxau-dkms
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
realtek-rtl88xxau-dkms
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/1787 kB of archives.
After this operation, 17.7 MB of additional disk space will be used.
Selecting previously unselected package realtek-rtl88xxau-dkms.
(Reading database ... 335440 files and directories currently installed.)
Preparing to unpack .../realtek-rtl88xxau-dkms_5.2.20.2~20190210-0kali1_all.deb ...
Unpacking realtek-rtl88xxau-dkms (5.2.20.2~20190210-0kali1) ...
Setting up realtek-rtl88xxau-dkms (5.2.20.2~20190210-0kali1) ...
Loading new realtek-rtl88xxau-5.2.20.2~20190210 DKMS files...
It is likely that 4.14.120 belongs to a chroot's host
Building for 4.14.120
Building initial module for 4.14.120
Done.

88XXau.ko:
Running module version sanity check.

• Original module
  • No original module exists within this kernel
• Installation
  • Installing to /lib/modules/4.14.120/updates/

depmod...

DKMS: install completed.

... and, in case it's helpful, here's the dmesg output taken after I plugged in the adaptor:

[ 40.638714] usb 3-1.2: new high-speed USB device number 3 using xhci-hcd
[ 40.743188] usb 3-1.2: New USB device found, idVendor=0bda, idProduct=8812
[ 40.748605] usb 3-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 40.755892] usb 3-1.2: Product: 802.11n NIC
[ 40.760067] usb 3-1.2: Manufacturer: Realtek
[ 40.764297] usb 3-1.2: SerialNumber: 123456
[ 40.823097] r8152 6-1:1.0 eth0: carrier on
[ 40.857233] RTL871X: module init start
[ 40.859531] RTL871X: rtl8812au v4.3.14_13455.20150212_BTCOEX20150128-51
[ 40.866831] RTL871X: rtl8812au BT-Coex version = BTCOEX20150128-51
[ 41.017095] RTL871X: rtw_ndev_init(wlan0)
[ 41.021389] usbcore: registered new interface driver rtl8812au
[ 41.025806] RTL871X: module init ret=0
[ 41.051557] 88XXau: loading out-of-tree module taints kernel.
[ 41.076646] usbcore: registered new interface driver rtl88xxau
[ 41.155527] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 41.586442] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 41.695466] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 41.772233] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 45.061800] logitech-hidpp-device 0003:046D:1017.0005: HID++ 1.0 device connected.
[ 47.202410] RTL871X: rtw_set_802_11_connect(wlan0) fw_state=0x00000008
[ 47.438214] RTL871X: start auth
[ 47.442039] RTL871X: auth success, start assoc
[ 47.533756] RTL871X: rtw_cfg80211_indicate_connect(wlan0) BSS not found !!
[ 47.539191] RTL871X: assoc success
[ 47.634256] RTL871X: send eapol packet
[ 47.639049] RTL871X: send eapol packet
[ 47.641445] RTL871X: set pairwise key camid:4, addr:60:38:e0:b5:08:3a, kid:0, type:AES
[ 47.641941] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
[ 47.652547] RTL871X: set group key camid:5, addr:60:38:e0:b5:08:3a, kid:2, type:AES
root@kali:~#

That dmesg output seems like its using the built in module for the wifi still...

Can you run "modinfo rtl8812au" (I believe is the module name) - and make sure it's using the correct one?

You may have to move the /lib/modules/4.14.xx/kernel/drivers/net/wireless/rtl8812au/rtl8812au.ko file out of the way and re-run depmod after doing so, and then either reboot, or modprobe -r the module and re-plug in the wifi device.

You found the problem! I'm not sure how it happened, but there was a second subdirectory, /lib/modules/4.14.xx/kernel/drivers/net/wireless/rtl8812au/. There was also a realtek subdirectory at the same level in the directory tree. I renamed the subdirectories and ran a series of tests to see what was going on. I removed and re-installed the realtek-rtl88xxau-dkms package, which recreated the appropriate files and folders it needed. And now, everything is fine. FWIW, if anybody else runs into this problem, the /lib/modules/4.14.xx/kernel/drivers/net/wireless/rtl8812au/ subdirectory should be deleted (or renamed).

Than you SO MUCH!! You are truly 'DA MAN!!"

Aargh.. may have spoken too soon. Stand by, still digging....

Here's an interim status report: i can get the AWUS036ACH to go into monitor mode, and run the aircrack suite and kismet, etc. However, I cannot get the adaptor to work as a normal wifi device. It's monitor mode or nothing. Worse yet, I also have an Atheros-based adaptor (AWUS036NHA) that doesn't work at all if the system is configiured for the ACH device. Ultimately, I'd like to be able to insert either adaptor and have them connect normally (without having to jump through hoops), and I should be able to run airmon-ng start wlan0 to put the adaptor in monitor mode. I'm pleased that the ACH adaptor can be used in monitor mode. Is it unrealistic to expect the system to support two different adaptors, and to be able to slip in and out of monitor mode ?

That isn't an unreasonable expectation at all, and it should work. Can you provide dmesg output? lsmod output? Need to see what's actually going on for you there.

reboot
plug in Atheros adaptor
dmesg:
[ 281.124118] usb 3-1.2: new full-speed USB device number 3 using xhci-hcd
[ 281.230016] usb 3-1.2: New USB device found, idVendor=10c4, idProduct=ea60
[ 281.235436] usb 3-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 281.242748] usb 3-1.2: Product: CP2102N USB to UART Bridge Controller
[ 281.249137] usb 3-1.2: Manufacturer: Silicon Labs
[ 281.253813] usb 3-1.2: SerialNumber: b2c2817e433ee911a9c1e2e3cabfe8c2
[ 281.286624] usbcore: registered new interface driver usbserial
[ 281.291104] usbcore: registered new interface driver usbserial_generic
[ 281.297773] usbserial: USB Serial support registered for generic
[ 281.306551] usbcore: registered new interface driver cp210x
[ 281.310853] usbserial: USB Serial support registered for cp210x
[ 281.316782] cp210x 3-1.2:1.0: cp210x converter detected
[ 281.322703] usb 3-1.2: cp210x converter now attached to ttyUSB0
root@kali:~#
wtf??

lsmod:
Module Size Used by
cp210x 24576 0
usbserial 36864 1 cp210x
fuse 86016 3
appletalk 32768 0
ipx 28672 0
p8023 16384 1 ipx
p8022 16384 1 ipx
psnap 16384 2 appletalk,ipx
llc 16384 2 p8022,psnap
joydev 20480 0
input_leds 16384 0
hid_logitech_hidpp 28672 0
evdev 24576 7
hid_logitech_dj 20480 0
usbhid 45056 0
ina231_sensor 16384 0
w1_gpio 16384 0
wire 24576 1 w1_gpio
gpio_keys 20480 0
extcon_usb_gpio 16384 0
exynos_gpiomem 16384 0
uio_pdrv_genirq 16384 0
uio 20480 1 uio_pdrv_genirq
binfmt_misc 20480 1
ip_tables 24576 0
ipv6 372736 56
root@kali:~#

swapped out adaptor for *ACH

lsmod:
Module Size Used by
88XXau 1753088 0
cfg80211 479232 1 88XXau
rfkill 20480 3 cfg80211
blah, blah, blah

dmesg:
[ 460.559444] usb 3-1.2: USB disconnect, device number 3
[ 460.563909] cp210x ttyUSB0: cp210x converter now disconnected from ttyUSB0
[ 460.570153] cp210x 3-1.2:1.0: device disconnected
[ 465.992807] usb 3-1.1: new high-speed USB device number 4 using xhci-hcd
[ 466.097275] usb 3-1.1: New USB device found, idVendor=0bda, idProduct=8812
[ 466.102702] usb 3-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 466.110019] usb 3-1.1: Product: 802.11n NIC
[ 466.114145] usb 3-1.1: Manufacturer: Realtek
[ 466.118394] usb 3-1.1: SerialNumber: 123456
[ 466.185812] 88XXau: loading out-of-tree module taints kernel.
[ 467.040194] usbcore: registered new interface driver rtl88xxau
[ 467.042351] usb 3-1.1: USB disconnect, device number 4
[ 467.116944] usb 4-1.1: new SuperSpeed USB device number 3 using xhci-hcd
[ 467.141366] usb 4-1.1: Int endpoint with wBytesPerInterval of 512 in config 1 interface 0 altsetting 0 ep 133: setting to 64
[ 467.151389] usb 4-1.1: New USB device found, idVendor=0bda, idProduct=8812
[ 467.158010] usb 4-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 467.165351] usb 4-1.1: Product: 802.11n NIC
[ 467.169449] usb 4-1.1: Manufacturer: Realtek
[ 467.173654] usb 4-1.1: SerialNumber: 123456
[ 467.440384] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 467.918551] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 467.923039] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
[ 468.009920] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready

Thanks!

Things are much better now: reinstalled firmware-atheros, firmware-linux-free, and wicd. Both adaptors work in and out of monitor mode, and can be swapped out as desired. I'm a happy puppy! Thanks for all your suppoort!!!

Apparently the upstream driver name is 88XXau.ko so you should be safe to simply create a file in /etc/modprobe.d/ called something like blacklist-rtl8812au.conf with the contents of "blacklist rtl8812au" instead of deleting the files