When playing tekkit classic, all mobs will have glitched textures, and some of their body parts will be missing. everything else works just fine.
If it matters, I have ubuntu 14.04 LTS, typing "java -version" in terminal gives
"java version "1.7.0_91" OpenJDK Runtime Environment (IcedTea 2.6.3) (7u91-2.6.3-0ubuntu0.14.04.1) OpenJDK 64-Bit Server VM (build 24.91-b01, mixed mode)"