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If you don't have a username/password, or your username/password is failing, ask one of the Online people to add one or update it for you. It is better if you don't masquerade as someone else, but acknowledged that it is sometimes unavoidable.
What to enter
During LAT I&T, we found that it is beneficial to make a log entry every time you start a run and another one every time a run completes. Note the run number in both cases and any peculiarities that may have shown up during the run. Also note any other activities like the trigger logic being changed in the NIM bins, that a computer rebooted, that you reset the VME crate, accesses to the cave, beam conditions, communications from (S)PS controls, unusual, or outside of your experience, behaviour (both hardware and software) of any part of the system, etc., etc. When in doubt, log it.