This isn't strictly Kubuntu, it's a new problem that's cropped up on one of my antiX systems (antiX is a very lightweight distro based on Debian, structurally and functionally similar to Lubuntu below the window manager level -- only lighter; antiX will run without special setup in less than 256 MiB RAM, reportedly as little as 128, and will run at command line in 64 MiB with a preconfigured swap partition). I'm hoping there's someone here who's seen a similar error and found a real fix for it.
After a recent dist-upgrade (Debian testing repos have frequent updates; I install them once a week), one of my antiX systems (Athlon XP 2000+ at 1.6 GHz, 1 GiB RAM, 40 GB HDD partitioned for Win98, root, swap, and home) started giving a message that "start job is running for dev-disk-by/x2duuid=<UUID>", with a 1:30 timer, for each of two devices, corresponding to the partitions for /home and swap -- but only when running an upgraded kernel version (that I've been running on that machine for many months); the system would start normally with the original 3.7.10-antix.2-486-smp kernel that installed with antiX 13.2, but kernel 3.12.6-antix.5-486-smp gave the "start job". Research suggested this error was most likely to appear when UUID was mismatched (it's apparently merely uncommon to have a swap partition quit working this way; the system will continue booting in that instance, but when /home is unmountable, you get command-line "emergency mode").
Very careful checking, even copy/paste of the UUID reported by lsblk -l or blkid -c /dev/null -o list into the appropriate fstab entries changed nothing; after researching fstab formats, labeling the three antiX partitions and changing fstab from UUID= format to LABEL= format also changed nothing. Examination of mtab when booted with the 3.7.10 kernel shows the /home partition still mounts as /sda4 even though / is mounted as "LABEL=" or "UUID=" -- and, naturally enough, when in emergency mode because those partitions fail to mount, they don't show in mtab at all.
The only suggestions I've had on the antiX forum were to remove a spurious entry found in the device.map (for Legacy GRUB, which installs with antiX) -- which did nothing -- and to run update-grub, which also did nothing (other than fill up menu.lst with the big block of "automagic" entries and add entries at the end for every combination of boot options for each kernel found). Does anyone know why a 3.12 series kernel would suddenly quit recognizing partitions mounted by UUID or label, while an older kernel would apparently ignore the fstab entries to mount those partitions by designator rather than specified identifier?