Which file contains systemwide environment and startup programs used by all users?

The file that contains systemwide environment and startup programs used by all users is /etc/profile. This file is executed whenever a user logs into the system, establishing environment settings and running initialization scripts. It typically includes paths, environment variables, and other configurations that should apply to all users on the machine.

In addition to /etc/profile, individual users can also have their own personal configuration files, such as .bashrc and .profile located in their home directories, but these affect only the individual user's environment. The key distinction is that /etc/profile is meant for all users, whereas the other files are user-specific. /etc/bash_profile is typically used for login shells and could be user-specific, while /.bashrc is commonly used for non-login shells.