Ubuntu establece la variable de entorno de forma permanente
#open terminal and type:
$ nano .bashrc
#scroll to the bottom of the script and type:
export <place variable name in here> = '<place variable value here>'
#e.g
export ANDROID_SDK_ROOT='/home/<$USER>/Android/Sdk'
#once you,re finished typing in your variable hit Ctrl+X then press enter
Faithful Frog