Here is the full list of all 18 Tech Support: Error Unknown achievements.
Unlock the achievement through the terminal
Finish a day with 12 tickets completed, under 45 seconds per completion and 5 stars.
Finish the game with no upgrades
Complete the game on professional
Buy every upgrade
Become a Lead Tech Support Specialist
Join the revolution against the corporate overlords
Rise the corporate ladder to success
Buy a residence away from it all
Help the law take down the culprits
Help your family in their time of need
Do your 8 to 5, no more, no less
Successfully complete 20 tickets in a day
Complete over 300 tickets total during the game
Help Jayesh with his sister
Get the 9.5 million dollars
Encounter the game's developer
Unlocked through the BIOS