Cannot set monitor mode.

[breisig]

Installed the latest rtl8821CU from git today on Linux kernel 5.4.14 using the following usb device.

USB ID 0bda:c811 Realtek Semiconductor Corp. 802.11ac NIC

[ 8.912689] 8821cu: no symbol version for module_layout [ 8.912705] 8821cu: loading out-of-tree module taints kernel. [ 9.000937] 8821cu: module verification failed: signature and/or required key missing - tainting kernel [ 9.011339] RTW: module init start [ 9.011341] RTW: rtl8821cu v5.4.1_28754.20180921_COEX20180712-3232 [ 9.011341] RTW: build time: Jan 24 2020 21:08:44 [ 9.011342] RTW: rtl8821cu BT-Coex version = COEX20180712-3232 [ 9.011462] RTW: [HALMAC]11692M HALMAC_MAJOR_VER = 1 HALMAC_PROTOTYPE_VER = 4 HALMAC_MINOR_VER = 19 HALMAC_PATCH_VER = 3 [ 9.012713] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.167885] RTW: HW EFUSE [ 9.167886] RTW: 0x000: 29 81 00 BC 09 00 31 00 6F 04 A4 10 12 00 30 0B [ 9.167889] RTW: 0x010: 23 23 23 24 24 24 2B 2B 2B 2C 2C 02 FF FF FF FF [ 9.167891] RTW: 0x020: FF FF 2B 2A 28 28 27 27 28 28 29 29 27 29 29 29 [ 9.167893] RTW: 0x030: 24 FF FF FF FF FF D0 FF FF FF 23 23 23 24 24 24 [ 9.167894] RTW: 0x040: 2B 2B 2B 2C 2C 02 FF FF FF FF FF FF FF FF FF FF [ 9.167896] RTW: 0x050: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167898] RTW: 0x060: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167899] RTW: 0x070: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167901] RTW: 0x080: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167903] RTW: 0x090: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167905] RTW: 0x0A0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167906] RTW: 0x0B0: FF FF FF FF FF FF FF FF 7F 06 1A 00 FF FF FF FF [ 9.167908] RTW: 0x0C0: FF 22 00 41 00 00 00 00 00 FF 22 FF FF FF FF FF [ 9.167910] RTW: 0x0D0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167912] RTW: 0x0E0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167913] RTW: 0x0F0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167915] RTW: 0x100: DA 0B 11 C8 C3 46 02 40 A5 EF 4E 92 81 09 03 52 [ 9.167917] RTW: 0x110: 65 61 6C 74 65 6B 0E 03 38 30 32 2E 31 31 61 63 [ 9.167919] RTW: 0x120: 20 4E 49 43 08 03 31 32 33 34 35 36 FF FF FF FF [ 9.167920] RTW: 0x130: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167922] RTW: 0x140: FF FF FF FF 00 00 31 0F FF FF FF FF FF FF FF FF [ 9.167924] RTW: 0x150: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167926] RTW: 0x160: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167927] RTW: 0x170: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167929] RTW: 0x180: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167931] RTW: 0x190: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167932] RTW: 0x1A0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167934] RTW: 0x1B0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167936] RTW: 0x1C0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167938] RTW: 0x1D0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167939] RTW: 0x1E0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.167941] RTW: 0x1F0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF [ 9.168106] RTW: hal_com_config_channel_plan chplan:0x7F [ 9.176970] RTW: [HALMAC][ALWAYS]shall R reg twice!! [ 9.178990] RTW: WARN [HALMAC][WARN]H2C/C2H ver is compatible!! [ 9.266895] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.267083] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.267268] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.267440] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.267610] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.267780] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.267950] RTW: ERROR [HALMAC][ERR]Dump efuse in suspend [ 9.268445] RTW: rtw_regsty_chk_target_tx_power_valid return _FALSE for band:0, path:0, rs:0, t:-1 [ 9.270326] RTW: rtw_ndev_init(wlan0) if1 mac_addr=40:a5:ef:4e:92:81 [ 9.270661] usbcore: registered new interface driver rtl8821cu [ 9.270662] RTW: module init ret=0 [ 9.338068] RTW: [HALMAC][ALWAYS]shall R reg twice!! [ 9.339961] RTW: WARN [HALMAC][WARN]H2C/C2H ver is compatible!! [ 10.184918] RTW: wlan0- hw port(0) mac_addr =40:a5:ef:4e:92:81

I checked the Makefile and monitor is enabled. CONFIG_WIFI_MONITOR = y

But when I try to run airodump-ng, it says it cannot set monitor mode root@server ~# airmon-ng check kill root@server ~# airmon-ng start wlan0

PHY Interface Driver Chipset

phy0 wlan0 rtl8821cu Realtek Semiconductor Corp. 802.11ac NIC

Newly created monitor mode interface wlan0mon is NOT in monitor mode. Removing non-monitor wlan0mon interface...

WARNING: unable to start monitor mode, please run "airmon-ng check kill"

Of course I tried 'airmon-ng check kill' but nothing happens.

[WingsLikeEagles]

As it says in the README, you need to use the following line to enable monitor mode: iw dev wlan0 set monitor none

[Bramzor]

iw dev wlan0 set monitor none

iw dev wlan0 set monitor none command failed: Operation not supported (-95)

[AndyM48]

Got the same error and realised that usb_modeswitch had not worked. Ran it again in a terminal, and the error went away.