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:

red

Kernel boot - when there are no running user space programs. red may also be used to indicate an error condition.

amber

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 S (startup), 0 (halt) and 6 (reboot). Single user mode (1) and Redboot permit user action and the light will be a steady amber.

green

User mode - one of the five multi-user runlevels 2-5. Normal user interaction with the system should be possible when the light is solid green.

off

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:

amber

Within RedBoot or initial kernel bootstrap.

red

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.