# Customize the TERR Environment at Startup

A user or an administrator can specify a variety of files, environment variables, and functions to customize a TERR session. These options are processed when the session starts. Changing them does not affect the current session of TERR.

Startup options are run in order and include the following.

1. TERRenviron files
2. TERRprofile files
3. .TERRData files
4. `.First` function

For both `TERRenviron` and `TERRprofile`, you can specify site-specific and user-specific files, which are processed in that order. Optionally, you can specify them as environment variables rather than files.

You can bypass running individual or all startup options by passing flags.

Optional startup flags | Description
--- | ---
`--vanilla` | All startup options ignored.
`--no-environ` | All `TERRenviron` files and environment variables are ignored.
`--no-site-file` | All site-specific profile files and environment variables are ignored.
`--no-init-file` | All user-specific profile files and environment variables are ignored.

This flowchart shows you how these options are processed at startup.