So I upgraded my Dell m3800 to Kubuntu 15.10, after which I'm only able to connect to my home wifi network. Every other network I try using doesn't work, including many that worked prior to upgrading. Points of potential interest:

  • In this instance "doesn't work" means: it connects to the other networks, but it looks like no data is ever received (the network-manager icon says X KiB/s sent/received, and the sent will frequently show non-zero values but received seems never to show a non-zero value).
  • I've tried the proposed solutions at Wifi losing connection, weak signal, Intel 7260 adapter (various iwlwifi module options) and http://ubuntuforums.org/showthread.php?t=2300362 (latest iwlwifi microcode).
  • I've tried purging and reinstalling the network-manager package.
  • I've tried connecting an external USB wifi adapter (with a Broadcom chip, not Intel like the internal wifi chip) and got exactly the same result. This is when I realised something very strange is going on.
  • I've googled around and found various other "wifi not working after upgrade issues" but they all seemed specific to Broadcom chips.

Here's the output of the wireless-info script when connected to a wifi network that my laptop used to work with but now doesn't: https://www.dropbox.com/s/sz858edudvpzgjj/wireless-info.txt?dl=0

And for comparison here's the output of the script when connected to (the one and only) wifi network that my laptop still works with: https://www.dropbox.com/s/s8jfxut810c1r2d/wireless-info.working.txt?dl=0

Inadvertently figured it out. After several months. Gah. The problem lay with the name resolution configuration (DNS settings). The settings I had worked with my home wifi but were incompatible with every other wifi network I tried. I only found out because I noticed that a service accessing a personal server of mine was working when my laptop was connected to some other wifi network, and the IP address for that server is set in /etc/hosts so no name resolution was required for it. After some digging around it turns out I needed to change the IP address for the name resolution service used by network-manager, defined in /etc/resolv.conf, from 192.168.1.1 to 127.0.1.1 (and then "sudo service network-manager restart").

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