RadHat / CentOs

0 — Halt

1 — Single-user text mode

2 — Not used (user-definable)

3 — Full multi-user text mode

4 — Not used (user-definable)

5 — Full multi-user graphical mode (with an X-based login screen)

6 — Reboot

Debian / Ubuntu

0 — Halt

1 — Single-user text mode

2 — Full multi-user graphical mode (with an X-based login screen)

3 — Not used (user-definable)

4 — Not used (user-definable)

5 — Not used (user-definable)

6 — Reboot

Suse

0 — Halt

1 — Single-user text mode

2 — Local multiuser mode without remote network (e.g., NFS)

3 — Full multiuser mode with network

4 — Not used (user-definable)

5 — Full multi-user graphical mode (with an X-based login screen)

6 — Reboot