@second.exodous You’ll have to tell Minecraft the correct java path instead of /bin/java.
Whether you’re using the Vanilla Launcher, FTB Launcher, or my favorite MultiMC, there is an options page that lets you tell it which java to specify. It should say Java Runtime or Java Path, and it may be blank (to use system pathing) or have a variable in it.
As an example of what to paste in the box instead, my java8 is:
which I found with
find /usr/ -name java
If your intent is to change the system default java from 7 to 8, you can do that by rewriting the symlinks in /usr/lib/jvm, which look like this on a system where the default is java 8:
lrwxrwxrwx 1 root root 14 Dec 11 12:06 default -> java-8-openjdk
lrwxrwxrwx 1 root root 18 Dec 11 12:06 default-runtime -> java-8-openjdk/jre
drwxr-xr-x 6 root root 4096 Dec 11 12:06 java-8-openjdk