I've got a bit confused about the behavior of the system so I restarted
the process to check what's happening. Here the steps I performed:
1. Install clean image on SD card.
2. Block internet access of the RPI, so no updates to be installed on first
boot.
3. Reboot
4. Remove 50-cloud-init.yaml from /etc/netplan
5. Create eth0-dhcp.yaml in /etc/netplan with the following content:
network:
version: 2
ethernets:
eth0:
dhcp4: true
dhcp6: false
optional: true
6. Create wlan0-dhcp.yaml in /etc/netplan with the following content:
network:
version: 2
wifis:
wlan0:
optional: true
access-points:
"SSID":
password: "PASS"
dhcp4: true
dhcp6: false
7. Execute "netplan try" and "netplan apply"
8. Reboot
9. At that point the kernel is "linux-image-5.3.0-1007-raspi2" and both
adapters are connected, have their IPs and SSH is possible to both.
10. Remove ethernet cable from RPI.
11. SSH over wlan0 IP is possible.
12. Reboot
13. Check SSH over wlan0 IP - still possible.
14. Unblock internet access of the RPI and run "sudo apt-get update"
15. Install newest kernel "linux-image-5.3.0-1012-raspi2": sudo apt install
linux-image-5.3.0-1012-raspi2
16. Reboot
17. SSH over wlan0 IP - NOT possible (connection time out)
18. Connect ethernet cable.
19. Check again SSH over wlan0 IP - NOT possible (connection time out)
20. Check SSH over eth0 IP - connection possible, but after 5-10 minutes of
waiting.
21. Install net tools: "sudo apt install net-tools"
22. ifconfig show that only eth0 is connected. wlan0 is up, but don't have IP.
23. Reboot
24. SSH possible over eth0 and wlan0. ifconfig confirm that both adapters have
their IPs.
25. Remove ethernet cable from RPI.
26. SSH not possible to wlan0.
27. Connect ethernet cable - SSH still not possible to either eth0, nor wlan0.
28. Hard reset of the RPI to reboot it - remove power supply.
29. SSH over eth0 possible. ifconfig show that wlan0 is up, but don't have IP.
I performed the same steps with "linux-image-5.3.0-1013-raspi2" and the results
are the same.
As a summaryI would say that "linux-image-5.3.0-1007-raspi2" have no
issues with plug-in, pulg-out of the ethernet cable. wlan0 and eth0
seem to work independently and together without issues.
With kernels above the before mentioned, plug-in/pulg-out of the
ethernet cable disrupt wlan0 and without the cable, SSH (or ping) is not
possible to wlan0.
Tried to revert the kernel to 1007 (on another clean image) as you
suggested, but after reboot I no longer can establish SSH to RPI. And as
I'm running headless, I don't know if the RPI actually booted or it's a
connection issue.
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https://bugs.launchpad.net/bugs/1853030
Title:
No connection through SSH over WIfi after kernel update
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux-raspi2/+bug/1853030/+subscriptions
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