In releases after (but not including) OpenSlug 1.12 OpenSlug changes the Ready/Status light to indicate boot progress. The light supports three colours - red, green and amber - and off.
The colour indicates the run level as follows:
- Kernel boot - when there are no running user space programs.
red may also be used to indicate an error condition.
- User space startup or shutdown, single user mode, RedBoot. Startup and shutdown are temporary states, the light should only be solid amber for a brief time. These states correspond to UNIX run levels
0 (halt) and
6 (reboot). Single user mode (
1) and Redboot permit user action and the light will be a steady amber.
- User mode - one of the five multi-user runlevels
5. Normal user interaction with the system should be possible when the light is solid green.
- Indicates either a powered down system (the LED inside the power button will be off) or a hung system (the LED inside the power button will be on, but the power button will not work.)
When the system transitions between two UNIX run levels the ready/status LED will alternate between the colours of the two levels. If the two levels use the same colour - for example transitions between user runlevels - the light will simply flash on/off.
During initial boot the light colour is controlled by RedBoot as follows:
- Within RedBoot or initial kernel bootstrap.
- Solid, set as soon as the LED code is initialised and maintained until user-space bootstrap starts (when the light should start flashing amber.)
RedBoot also uses an alternate red/green flash while in
upgrade mode waiting for a download to start. During the download the flashing continues but is intermittent - it only happens while the NSLU2 is waiting for data from the upload host.