I'm using Ubuntu 16.04. My wifi worked just as normal two days ago, but today it was suddently broken. Normally, there should be an "enable wifi" option on the top panel bar, but I couldn't see it today.
but I couldn't see any device that's related to wifi.
DEVICE TYPE STATE enp5s0 ethernet unavailable lo loopback unmanaged
Therefore, I spent 3 hours searching for lots of forums, but still couldn't solve the problem. This is all the websites I had viewed during that 3 hours:
http://www.wallcopper.com/linux/2596.html https://unix.stackexchange.com/questions/234452/nmcli-device-eth1-unavailable https://www.linuxquestions.org/questions/linux-networking-3/nmcli-device-eth1-unavailable-4175555503/ https://bbs.archlinux.org/viewtopic.php?id=231991 https://wiki.archlinux.org/index.php/Network_configuration#Device_names https://stackoverflow.com/questions/45691434/nmcli-device-unavailable https://askubuntu.com/questions/855240/ubuntu-16-04-how-to-re-enable-wifi https://askubuntu.com/questions/946235/unable-to-activate-enable-wireless https://askubuntu.com/questions/71159/network-manager-says-device-not-managed https://nullr0ute.com/2016/09/connect-to-a-wireless-network-using-command-line-nmcli/ https://askubuntu.com/questions/900568/connection-could-not-be-found https://fedoraproject.org/wiki/Networking/CLI https://unix.stackexchange.com/questions/236514/how-do-i-attach-devices-to-connections-using-nmcli https://unix.stackexchange.com/questions/158328/network-manager-not-listing-wifi https://askubuntu.com/questions/715345/network-manager-is-not-detecting-wifi-networks/921392#921392 https://ask.fedoraproject.org/en/question/64217/how-to-connect-to-wifi-using-nmcli/ https://ubuntuforums.org/showthread.php?t=2354066&page=5 https://ubuntuforums.org/showthread.php?t=2214911 https://ubuntuforums.org/showthread.php?t=1195312 https://ubuntuforums.org/showthread.php?t=1314693 https://ubuntuforums.org/showthread.php?t=2381037 https://askubuntu.com/questions/858546/wifi-not-working-intel-on-hp-spectre-x360-13/859263#859263 https://ubuntuforums.org/showthread.php?t=2356217 https://askubuntu.com/questions/996178/network-unclaimed-ubuntu-16-04?rq=1 https://superuser.com/questions/1288879/ubuntu-16-04-cannot-detect-wifi https://medium.com/@lgobinath/no-ethernet-connection-in-ubuntu-16-04-linux-mint-18-with-realtek-rtl8111-8168-8411-7ae2779dc9b8 https://unix.stackexchange.com/questions/417262/network-unclaimed-ubuntu-16-04 https://answers.launchpad.net/ubuntu/+source/gnome-nettool/+question/657341
I was exhausted and frustrated, because I couldn't do what I had planned to do tonight and I also couldn't fix my wifi. Fortunately, I read a line in the last link above, that I could reboot and choose a previous kernel version. I remember that I was in 4.15.0-33 a few days ago, but now I was in 4.15.0-34 instead. After I changed to the previous version, my wifi just started working.....
WTF IS KERNEL 4.15.0-34 DOING?? I've spent 3 hours worthlessly just dealing with that stupid update! I mean, this is such a meaningless thing to do, for one spending lots of time just to figure out there's a kernel update that's not compatible with a particular driver. Shouldn't this be the responsibility of the dev?
This lesson teaches us: When there's a weird problem on Linux, always try to roll back to a previous kernel version.