As of october 2018, disk quota are enforced on the Home Directory Servers. That means you cannot write more data to $HOME than the allotted quotum. The server will act as if your disk is full. To reduce the chance this causes problems, there is a grace period of 7 days where you can exceed the quotum up to 10 Gb.
Quota info at login
Every time you log in, a notification message will show your current data usage and quota like this:
A message like this will appear at login and every 30 minutes when your home directory usage has exceeded quota by less than 10 Gb for less than 7 days:
(note that it shows when the grace period of 10 Gb extra space will end.)
When your home directory usage exceeds quota by more than 10Gb, or by less than 10 Gb but longer than 7 days, you cannot write to your home directory anymore. Among (probably) other error dialogs from other program complaining they can not write files anymore, messages like this will appear every 30 minutes:
Q: How much quotum do I have?
A: As of Octobre 2018 quota will initially be set to 10 Gb more than your data usage, with a minimum of 50 Gb.
Q: What if I exceed my quotum?
A: A warning dialog will show every 30 minutes, showing the quota information. You will still be able to write to your home directory, as there is a fall-back of 10 Gb extra.
However when you exceed this fall-back limit (also called "hard limit") your programs won't be able to write anymore and will be in "disk full" condition.
The fall-back of 10 Gb extra also will expire in 7 days after first exceeding the limit. When it expires, "disk full" condition will apply as if the (hard) limit was reached.
Q: I need more space. What do I do?
A: Either delete some file you do not need anymore, or ask for more space (quotum). Generally your quotum will be increased by return, if server disk space allows. However, if you need considerably more than, say 100 Gb, we will ask you request a "project directory" and store the bulk of your files there. See: Project Directories.
Q: I exceeded my quota. All my programs started complaining, and I can't work any more. I can't even log in any more.
A: That's a pity. In the worst case, press <CTR><F2> to get to a text-mode prompt. Log in, and delete some stuff until there is free space. After you logged out, <CTRL><F7> to get back to a graphics mode screen, and perhaps reboot. You should be able to work again.
Q: Quota are a nuisance! Why do we have to have them!?!
A: If large file systems break, fixing them takes weeks. So we want small filesystems. But if one single user writes too much data, all your lwps stop working. And on a small filesystem, the risk is considerable.
Q: Why this artificial split between $HOME and /project?
A: All your programs (shells, editors, browsers, mail, Matlab, etc. etc.) write to $HOME by default. If $HOME is full, all of those break, and some corrupt their data - silently, if you have bad luck. We don't want this for any significant number of users. If /project (or part of it) overflows, only the programs break that were specifically directed to it. That's still bad, but not at all as bad as all your programs failing.