No Way Know How

I managed this more or less by myself. sudo pacman -S linux-lts linux-headers-lts Installing the lts kernel will prompt for the headers, so you might as well do them together. Then go to /boot and find the conf file, under loader or wherever. copy the file and append -lts to the linux img lines and vmlinuz-linux. then sudo bootctl update, reboot, and you should have the new entry in the UEFI boot menu.

The latitude is affected by this kernel bug: https://bugs.archlinux.org/task/46894 I should make a UEFI entry for booting to the LTS kernel, but I haven't got around to this yet. So in the meantime I think I'll do what's advised in this page: https://www.digitalocean.com/community/tutorials/pacman-syu-kernel-update-solved-how-to-ignore-arch-kernel-upgrades and add IgnorePkg = Linux to /etc/pacman.conf so the kernel isn't touched until the mainline resolves the bug. [edit: did this and updated. The next time I booted I had the same problem as before. downgraded the kernel and it worked again. Need to look at moving to LTS kernel, I think]