What is the maximum niceness value that a regular user can assign to a process with the nice command when executing a new process?

While 9 is a valid niceness value that a regular user can set, it is not the maximum possible value they can assign to decrease a process's priority.

The niceness value ranges from -20 (highest priority) to 19 (lowest priority). A regular user can only assign non-negative niceness values and can only increase the niceness (decrease priority), with 19 being the maximum value they can set.

49 is outside the standard niceness range, which typically extends only up to 19.

99 is outside the standard niceness range, which typically extends only up to 19.