how to revert changes on /etc/environment, which prevent a login

environment-variables

Restart your system, when starting press ESC to reach the grub bootmenu.

Start the recovery mode, open a root shell and revert the changes.

Related

How to add entry to /etc/hosts with a built-in command line
Log in loop following environment change
wget fails by a certificate problem
How do you purge a removed app? or delete snapshot after app removal
How to install package xorg-server
How do I deal with early Reapers as Zerg?
How can I make a lot of gil?
Banding question for Magic The Gathering (Duels of the Planeswalkers)
How does one's fishing level relate to what one catches and when one catches it?
Expedition planning in Die2Nite
How do you win the zombies mode in Call of Duty Black ops
How exactly do the tracer pistols work?