20.5. Run Levels

The following run levels are specified for use by the Default-Start and Default-Stop actions defined in Comment Conventions for Init Scripts as hints to the install_initd command. Conforming implementations are not required to provide these exact run levels or give them the meanings described here, and may map any level described here to a different level which provides the equivalent functionality. Applications may not depend on specific run-level numbers.

1single user mode
2multiuser with no network services exported
3normal/full multiuser
4reserved for local use, default is normal/full multiuser
5multiuser with a display manager or equivalent

Note: These run levels were chosen as reflecting the most frequent existing practice, and in the absence of other considerations, implementors are strongly encouraged to follow this convention to provide consistency for system administrators who need to work with multiple distributions.