monitor 模式是什么？
数据包通过无线电信号来传输，monitor模式下的网卡可以接收所有它可以接收的无线电信号并进行解析，不仅仅限于它所在的无线局域网。
那么ubuntu下的网卡的monitor模式如何开启呢？
第一步
首先使用命令查看当前的无线网卡支持哪些mode：
iw list
命令结果为 supported interface modes 有两个：
managed
monitor
Wiphy phy1
max # scan SSIDs: 4
max scan IEs length: 2257 bytes
Retry short limit: 7
Retry long limit: 4
Coverage class: 0 (up to 0m)
Supported Ciphers:
* WEP40 (00-0f-ac:1)
* WEP104 (00-0f-ac:5)
* TKIP (00-0f-ac:2)
* CCMP (00-0f-ac:4)
* 00-0f-ac:10
* GCMP (00-0f-ac:8)
* 00-0f-ac:9
Available Antennas: TX 0 RX 0
Supported interface modes:
* managed
* monitor
Band 1:
Capabilities: 0x172
HT20/HT40
Static SM Power Save
RX Greenfield
RX HT20 SGI
RX HT40 SGI
RX STBC 1-stream
Max AMSDU length: 3839 bytes
No DSSS/CCK HT40
Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
Minimum RX AMPDU time spacing: 2 usec (0x04)
HT TX/RX MCS rate indexes supported: 0-7, 32
Bitrates (non-HT):
* 1.0 Mbps (short preamble supported)
* 2.0 Mbps (short preamble supported)
* 5.5 Mbps (short preamble supported)
* 11.0 Mbps (short preamble supported)
* 6.0 Mbps
* 9.0 Mbps
* 12.0 Mbps
* 18.0 Mbps
* 24.0 Mbps
* 36.0 Mbps
* 48.0 Mbps
* 54.0 Mbps
Frequencies:
* 2412 MHz [1] (20.0 dBm)
* 2417 MHz [2] (20.0 dBm)
* 2422 MHz [3] (20.0 dBm)
* 2427 MHz [4] (20.0 dBm)
* 2432 MHz [5] (20.0 dBm)
* 2437 MHz [6] (20.0 dBm)
* 2442 MHz [7] (20.0 dBm)
* 2447 MHz [8] (20.0 dBm)
* 2452 MHz [9] (20.0 dBm)
* 2457 MHz [10] (20.0 dBm)
* 2462 MHz [11] (20.0 dBm)
* 2467 MHz [12] (20.0 dBm) (no IR)
* 2472 MHz [13] (20.0 dBm)
Supported commands:
* new_interface
* set_interface
* new_key
* start_ap
* new_station
* new_mpath
* set_mesh_config
* set_bss
* authenticate
* associate
* deauthenticate
* disassociate
* join_ibss
* join_mesh
* set_tx_bitrate_mask
* frame
* frame_wait_cancel
* set_wiphy_netns
* set_channel
* set_wds_peer
* probe_client
* set_noack_map
* register_beacons
* start_p2p_device
* set_mcast_rate
* Unknown command (104)
* connect
* disconnect
Supported TX frame types:
* IBSS: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* managed: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* AP: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* AP/VLAN: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* mesh point: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* P2P-client: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* P2P-GO: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* P2P-device: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
Supported RX frame types:
* IBSS: 0x40 0xb0 0xc0 0xd0
* managed: 0x40 0xd0
* AP: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
* AP/VLAN: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
* mesh point: 0xb0 0xc0 0xd0
* P2P-client: 0x40 0xd0
* P2P-GO: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
* P2P-device: 0x40 0xd0
software interface modes (can always be added):
* monitor
interface combinations are not supported
HT Capability overrides:
* MCS: ff ff ff ff ff ff ff ff ff ff
* maximum A-MSDU length
* supported channel width
* short GI for 40 MHz
* max A-MPDU length exponent
* min MPDU start spacing
Device supports TX status socket option.
Device supports HT-IBSS.
Device supports SAE with AUTHENTICATE command
Device supports low priority scan.
Device supports scan flush.
Device supports AP scan.
Device supports per-vif TX power setting
Driver supports a userspace MPM
Device supports active monitor (which will ACK incoming frames)
第二步
使用 iwconfig 可以查看网卡信息，其中可以看到我的网卡目前的模式是managed（而且名字很奇怪，不知道是否和使用虚拟机有关）
ens33 no wireless extensions.
lo no wireless extensions.
wlx30b49e22ab5b IEEE 802.11bgn ESSID:off/any
Mode:Managed Access Point: Not-Associated Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off
第三步
关闭这个无线网卡，然后将模式改为monitor，（不关闭则无法更改mode）
sudo ifdown （your device name）
这个我遇到了第一个问题，就是使用设备名无法识别，于是我选择从GUI中关闭。
成功的关闭后，就可以执行下一个命令:
sudo iwconfig wlx30b49e22ab5b mode moniter
然后我使用命令 sudo ifconfig （your device name）up 开启设备，返现不成功！返回为：
SIOCSIFFLAGS: Operation not possible due to RF-kill
这是因为你的网卡 是 Soft-blocking，我直接写出适合我的解决方法，原文中要重启电脑，但是我没有重启之前就成功了。
sudo rfkill unblock wifi
sudo rfkill unblock all
然后上一个设置mode的命令就可以成功的执行了
第四步
此时使用命令：
sudo ifconfig （your device name）up
可以成功的开启网卡
再一次使用 iwconfig 命令查看的时候，发现:
ens33 no wireless extensions.
lo no wireless extensions.
wlx30b49e22ab5b IEEE 802.11bgn Mode:Monitor Frequency:2.412 GHz Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off
网卡的模式已经变成了 Monitor 模式！
使用wireshark检测，使用此接口成功抓包！