Unit status

A unit can report its status as one of the following:

Status Colour in GUI Meaning
blocked blue This unit needs manual intervention because of a problem associated directly with the unit itself. This may be due to bad or inconsistent configuration of the application, disk space being unavailable for the unit, or missing relations which are essential to the application's operations. The message should tell a human administrator what is required to unblock the application.
For example: "Please provide an object store. Please configure the minimum speed required by users of this application. Please link this application to a database.".
Note that this status may also be transitory in the sense that processes underway have not yet completed.
maintenance yellow The unit is not yet providing services, but is actively doing stuff in preparation for providing those services. This is a “spinning” state, not an error state. It reflects activity on the unit itself, not on peers or related units. The Juju agent will set the unit to maintenance when it begins the process of installing the charm - downloading it, unpacking it and calling the install hook.
The unit may transition to the maintenance state at any time, in any hook. The maintenance state implies that the unit has no reason to think that it will not provide service soon. For example, the software might be formatting block devices, or replicating data from peer units, or handling an action which for whatever reason means that it is not active, but it is not aware of anything on its own config or in related unit config that will prevent it from bringing up its application.
Counterparts to this unit should expect that calls to this unit will fail during the period it is in the maintenance state, but unless they have an urgent need to move to another counterpart, they should just wait for this unit to finish churning.
Being in maintenance does not require human intervention.
waiting yellow The unit is unable to progress to an active state because an application to which it is related is not running. That application might be in error, blocked, waiting or maintenance. This unit expects it will be able to proceed towards active as soon as the things it is concerned about are resolved there - it needs no human attention (otherwise its status would be blocked).
active green This unit believes it is correctly offering all the services it is primarily installed to provide. An application can be active even if additional relations are being configured and set up. For example, a Ceph OSD application that is connected to its monitors is active, even if you then relate it to Nagios; setting up a subordinate does not impinge on the OSD functionality which is its primary purpose for existing.

Additional values may be seen for a unit which have been set by Juju rather than the charm, under the circumstances explained below:

Status Colour in GUI Meaning
error red A charm hook for this unit has exited with a non-zero exit code (crashed). No further hooks will be called or messages delivered until this is resolved; manually resolving or manually asking for the hook to be run, successfully, addresses the issue and resets the state to "unknown" with a message of "Error resolved with no further status from charm".
unknown yellow A unit-agent has finished calling install, config-changed, and start, but the charm has not called status-set yet. Rather than guess as to whether the application is working, Juju will set its status to "unknown". A unit is also marked as “unknown” when the unit agent fails for some reason eg loss of connectivity.
terminated none, CLI-only This unit used to exist, we have a record of it (perhaps because of storage allocated for it that was flagged to survive it). Nonetheless, it is now gone.

Note: The Colour in GUI is included for information at this point, until this feature is fully supported in the Juju GUI.