Actors: any user.
Outline: the user logs into the DAS computer, and selects a software
version. The system makes the server software
and the engineering interface available.
Typical course of events:
| User action | System response | |
| 1. | Logs in to DAS computer using a standard account. | Makes the obssys command available. |
| 2. | Runs obssys and chooses a version of software. | Defines the commands startobssys, shutdownobssys, dasreset, daseng to refer to the chosen version. Checks the version of software currently running; offers to shut down the sub-system if it is not the chosen version. |
| 3. | Opts to shut down running software of an unwanted version. | Shuts down all cameras, moving them to the "unclaimed" state. |
There should be one account for observing and routine maintenance. The password needs to be known to observers, change-crew members and duty engineers. The account is probably one of intobs, jktobs and whtobs, as in system s6. The obssys command for the DAS computer is not the same as the one for the system computer. The latter allows choices of system version, instrument and detector. The DAS command only allows a choice of system version, as the instrument name is passed to the DAS by the CIA and the sub-system works out the set of mounted detectors by itself. The defined commands are as follows: startobssys activate all cameras; put them in the on-line state. shutdownobssys deactivate all cameras; put them in the unclaimed state. udasreset shut down all cameras then start them up afresh; leave them in the on-line state. udaseng start the engineering interface. Opting not to shut down wrong-version software is an escape if the user has selected the wrong version in obssys and intends to re-run obssys. Otherwise, it's a silly thing to do.