Which run levels should never be declared as the default run level when using SysV init? (Choose TWO correct answers.)

Run level 0 is the system halt state; setting it as default would cause the system to power off immediately after init starts. Run level 6 is the reboot state; setting it as default would cause the system to continuously reboot in an infinite loop, making it completely unusable.

Run level 1 is single-user/maintenance mode; while uncommon as a default it is technically functional and sometimes used in restricted environments.

Run level 3 is a valid default - it is the standard full multiuser mode with networking but without a graphical display manager.

Run level 5 is a valid and common default - it is full multiuser mode with networking and a graphical display manager.

Run level 6 is the reboot state; setting it as default would cause the system to continuously reboot in an infinite loop, making it completely unusable.