Calendar Options for Linux Users
Since the shutdown of the "Corporate Time" (CTime) calendar tool some years ago, no DESY wide solution for a work calendar for Linux users has come up (although there is talk about a future solution, but it is unclear when this will appear).
The only official calendar is the one from Microsoft Exchange, which you can access from Linux either via the web frontend webmail.desy.de or using the Windows Terminal Server via Outlook. Since both options are not perfect (think of not-working reminder pop-ups), many Linux users use a private calendar, which has the disadvantage of not having the possibility to share events and it is not visible to other group members.
Setting up Lightning
Lightning is an add-on for the Thunderbird mail client. You can download it via the official file server.
Note: the version offered on the homepage does not work with the version 2 of Thunderboird which is preinstalled in Scientific Linux 5 versions at DESY.
The add-on is installed in Thunderbird as usual: goto Tools → Add-Ons → Install (at bottom of newly opened window) → choose the downloaded file and install it. The usage of Lightning should be pretty straight foward, some help can be found in the FAQ. Here you can easily create local (=private) calendars on your hard disk.
Tip: If you do not want to switch between the mail and the calendar view in Thunderbird: open one of your mail folders (right click → open) in a new window and choose in this window the calendar view. Unfortunately, Thunderbird doesn't remember this layout after a restart.
Tip: a file containing the dates german holidays from 2010-2015 can be found here; this you can import in Lightning.
Connecting to the Exchange server
For the setup that is currently used at DESY (Exchange Server 2003 and Thunderbird 2), there seems to be only one solution to connect the two. This is using DavMail as a local gateway server.
DavMail is a Java program that starts a local server which can read from the Exchange web front-end and offers a CalDav port to Lightning. You can download it here (under Linux (other)). The installation is described here. You can start the DavMail server by running davmail.sh. At the first start a setup menu should appear. How to set it up is described here. Since only the CalDav gateway is interesting in the DESY setup, all other should be un-ticked. For the OWA (Exchange) URL enter https://owa.desy.de/exchange/. After a successful start, a symbol should appear in your system tray.
Settings in Lightning
To connect to your exchange calendar, creat a new calendar in Lightning (right click in the list of your calendards in the calendar view). Choose "On the Network" and then "CalDaV". Location is of the form "http://localhost:firstname.lastname@example.org/calendar" (any addition like e.g. "/test" to this address would refer to a sub-calendar). The you can assign a nickname to this calendar . Login data would be "WIN/youusername" and your normal password.
Now everything should be working. Events entered in one over Lightning should appear under Outlook and vice versa. For detailed settings of your Exchange calendar, you might still have to use the Windows Terminal Server and do them using Outlook.