In Linux, which of the following files describes the processes that are started up during boot up?

/etc/passwd stores user account information such as usernames, UIDs, home directories, and default shells, and plays no role in defining boot-time processes.

/etc/profile is a shell script that configures system-wide environment variables and startup settings for interactive login shells, not the init daemon's process definitions.

/etc/inittab is read by the init daemon at startup and specifies the default runlevel along with which processes or services to start, stop, or respawn at each runlevel transition, making it the authoritative file for controlling boot-time process initialization in SysV-based Linux systems.

/etc/shadow stores encrypted user passwords and password aging policy, and has no involvement in the boot process or service initialization.