Sources: teradata-downloads, teradata-docs
Troubleshooting:
1. My system restarted while teradata was running. Unable to access/start teradata.
this happens due to unclean termination of teradata process. following commands helped:
/etc/init.d/tpa start # this indicated service cannot start properly as its already running.
/etc/init.d/tpareset -f force #this clears pid logs due to unclean termination.. now tpa start works.