I am running Ubuntu 14.04 in a RAID 1 configuration. How do I expand one of my LVM partitions as my /var partition is 100% filled up? I have tried to boot in rescue mode but gparted is not available in this mode.
If your Ubuntu installation is using Logical Volume Manager (LVM) then most likely your /var is actually a Logical Volume (LV) as compared with a traditional partition. The command to grow or shrink an LV is lvresize. You will also require empty space in the Physical Volume (PV) if you wish to grow the /var LV.
KDE Partition Manager might be able to resize it. It doesn't detect RAID yet, but latest unreleased version (will be released as 3.0 later) should be able to resize LVM logical volumes. Hopefully, no RAID support wouldn't interfere, but you don't need to resize LVM physical volumes.
Download Neon Developer Edition (Developer Git-Stable should be fine) from https://neon.kde.org/download Then run "apt install partitionmanager" start KDE Partition Manager and it should detect your LVM devices.