我需要在 Raspberry Pi 4 Model B 上安装 ROS。根据说明，最好从 Ubuntu-mate 发行版按照标准 ARM 说明进行操作
（http://wiki.ros.org/ROSberryPi/Installing%20ROS%20Melodic%20on%20the%20Raspberry%20Pi）
我已经将 Ubuntu 映像刷入 SD 卡，现在我尝试通过 SSH（Ubuntu Mate 20.04.1 arm64）访问我的 Raspberry Pi，但即使我已经在根目录中添加了 ssh 文件，它仍然拒绝连接。这是它在分区内的内容
G:\
¦ README
¦ bootcode.bin
¦ cmdline.txt
¦ config.txt
¦ fixup.dat
¦ fixup4.dat
¦ fixup4cd.dat
¦ fixup4db.dat
¦ fixup4x.dat
¦ fixup_cd.dat
¦ fixup_db.dat
¦ fixup_x.dat
¦ start.elf
¦ start4.elf
¦ start4cd.elf
¦ start4db.elf
¦ start4x.elf
¦ start_cd.elf
¦ start_db.elf
¦ start_x.elf
¦ bcm2710-rpi-2-b.dtb
¦ bcm2710-rpi-3-b-plus.dtb
¦ bcm2710-rpi-3-b.dtb
¦ bcm2710-rpi-cm3.dtb
¦ bcm2711-rpi-4-b.dtb
¦ bcm2837-rpi-3-a-plus.dtb
¦ bcm2837-rpi-3-b-plus.dtb
¦ bcm2837-rpi-3-b.dtb
¦ bcm2837-rpi-cm3-io3.dtb
¦ boot.scr
¦ initrd.img
¦ overlay_map.dtb
¦ syscfg.txt
¦ uboot_rpi_3.bin
¦ uboot_rpi_4.bin
¦ usercfg.txt
¦ vmlinuz
¦ ssh
¦
+---overlays
adau7002-simple.dtbo
act-led.dtbo
adafruit18.dtbo
adau1977-adc.dtbo
akkordion-iqdacplus.dtbo
ads1015.dtbo
ads1115.dtbo
ads7846.dtbo
adv7282m.dtbo
adv728x-m.dtbo
audioinjector-addons.dtbo
anyspi.dtbo
allo-boss-dac-pcm512x-audio.dtbo
allo-digione.dtbo
allo-katana-dac-audio.dtbo
allo-piano-dac-pcm512x-audio.dtbo
allo-piano-dac-plus-pcm512x-audio.dtbo
apds9960.dtbo
applepi-dac.dtbo
at86rf233.dtbo
dionaudio-loco-v2.dtbo
audremap.dtbo
audioinjector-isolated-soundcard.dtbo
audioinjector-ultra.dtbo
audioinjector-wm8731-audio.dtbo
audiosense-pi.dtbo
balena-fin.dtbo
cma.dtbo
dht11.dtbo
dionaudio-loco.dtbo
disable-bt.dtbo
disable-wifi.dtbo
dpi18.dtbo
dpi24.dtbo
draws.dtbo
dwc-otg.dtbo
dwc2.dtbo
enc28j60-spi2.dtbo
enc28j60.dtbo
exc3000.dtbo
fe-pi-audio.dtbo
goodix.dtbo
googlevoicehat-soundcard.dtbo
gpio-fan.dtbo
gpio-ir-tx.dtbo
gpio-ir.dtbo
gpio-key.dtbo
gpio-no-bank0-irq.dtbo
gpio-no-irq.dtbo
gpio-poweroff.dtbo
gpio-shutdown.dtbo
hd44780-lcd.dtbo
hdmi-backlight-hwhack-gpio.dtbo
hifiberry-amp.dtbo
hifiberry-dac.dtbo
hifiberry-dacplus.dtbo
hifiberry-dacplusadc.dtbo
hifiberry-dacplusadcpro.dtbo
hifiberry-dacplusdsp.dtbo
hifiberry-dacplushd.dtbo
hifiberry-digi-pro.dtbo
hifiberry-digi.dtbo
highperi.dtbo
hy28a.dtbo
hy28b-2017.dtbo
hy28b.dtbo
i-sabre-q2m.dtbo
i2c-bcm2708.dtbo
i2c-gpio.dtbo
i2c-mux.dtbo
i2c-pwm-pca9685a.dtbo
i2c-rtc-gpio.dtbo
i2c-rtc.dtbo
i2c-sensor.dtbo
i2c0.dtbo
i2c1.dtbo
i2c3.dtbo
i2c4.dtbo
i2c5.dtbo
i2c6.dtbo
i2s-gpio28-31.dtbo
ilitek251x.dtbo
imx219.dtbo
imx290.dtbo
imx477.dtbo
iqaudio-codec.dtbo
iqaudio-dac.dtbo
iqaudio-dacplus.dtbo
iqaudio-digi-wm8804-audio.dtbo
irs1125.dtbo
jedec-spi-nor.dtbo
justboom-both.dtbo
justboom-dac.dtbo
justboom-digi.dtbo
ltc294x.dtbo
max98357a.dtbo
maxtherm.dtbo
mbed-dac.dtbo
mcp23017.dtbo
mcp23s17.dtbo
mcp2515-can0.dtbo
mcp2515-can1.dtbo
mcp3008.dtbo
mcp3202.dtbo
mcp342x.dtbo
media-center.dtbo
merus-amp.dtbo
midi-uart0.dtbo
midi-uart1.dtbo
miniuart-bt.dtbo
mmc.dtbo
mpu6050.dtbo
mz61581.dtbo
ov5647.dtbo
ov7251.dtbo
ov9281.dtbo
overlay_map.dtb
papirus.dtbo
pca953x.dtbo
pibell.dtbo
pifacedigital.dtbo
piglow.dtbo
piscreen.dtbo
piscreen2r.dtbo
pisound.dtbo
pitft22.dtbo
pitft28-capacitive.dtbo
pitft28-resistive.dtbo
pitft35-resistive.dtbo
pps-gpio.dtbo
pwm-2chan.dtbo
pwm-ir-tx.dtbo
pwm.dtbo
qca7000.dtbo
rotary-encoder.dtbo
rpi-backlight.dtbo
rpi-cirrus-wm5102.dtbo
rpi-dac.dtbo
rpi-display.dtbo
rpi-ft5406.dtbo
rpi-poe.dtbo
rpi-proto.dtbo
rpi-sense.dtbo
rpi-tv.dtbo
rpivid-v4l2.dtbo
rra-digidac1-wm8741-audio.dtbo
sainsmart18.dtbo
sc16is750-i2c.dtbo
sc16is752-i2c.dtbo
sc16is752-spi0.dtbo
sc16is752-spi1.dtbo
sdhost.dtbo
sdio.dtbo
sdtweak.dtbo
sh1106-spi.dtbo
smi-dev.dtbo
smi-nand.dtbo
smi.dtbo
spi-gpio35-39.dtbo
spi-gpio40-45.dtbo
spi-rtc.dtbo
spi0-1cs.dtbo
spi0-2cs.dtbo
spi0-cs.dtbo
spi0-hw-cs.dtbo
spi1-1cs.dtbo
spi1-2cs.dtbo
spi1-3cs.dtbo
spi2-1cs.dtbo
spi2-2cs.dtbo
spi2-3cs.dtbo
spi3-1cs.dtbo
spi3-2cs.dtbo
spi4-1cs.dtbo
spi4-2cs.dtbo
spi5-1cs.dtbo
spi5-2cs.dtbo
spi6-1cs.dtbo
spi6-2cs.dtbo
ssd1306-spi.dtbo
ssd1306.dtbo
ssd1351-spi.dtbo
superaudioboard.dtbo
sx150x.dtbo
tc358743-audio.dtbo
tc358743.dtbo
tinylcd35.dtbo
tpm-slb9670.dtbo
uart0.dtbo
uart1.dtbo
uart2.dtbo
uart3.dtbo
uart4.dtbo
uart5.dtbo
udrc.dtbo
upstream-pi4.dtbo
upstream.dtbo
vc4-fkms-v3d.dtbo
vc4-kms-kippah-7inch.dtbo
vc4-kms-v3d-pi4.dtbo
vc4-kms-v3d.dtbo
vga666.dtbo
w1-gpio-pullup.dtbo
w1-gpio.dtbo
w5500.dtbo
wittypi.dtbo
我可以看到我的设备已连接到路由器，并且已分配给它一个 IP 地址，但是当我尝试 SSH 时连接被拒绝。
有什么线索吗？