Quotas on the CS Linux Machines: FAQ

Questions that are frequently asked, or maybe should be, about quotas as implemented on the CS classroom/lab Linux machines.

  1. What are quotas anyway?

    They're a mechanism provided by Linux (and other UNIX-like) filesystems for limiting total size of each user's files. (Why bother? See below.) Every time you create a new file, or make an existing file bigger, the system is supposed to check to make sure total space doesn't exceed whatever limit was set for your account. If it does, you're ``over quota'', and you have a grace period of about a week to do something about it -- either delete some files or ask for a larger quota.

  2. I keep getting this e-mail message about disk space usage on my account exceeding my quota. What does it mean and how do I make it stop?

    It means what it says -- you're over quota -- and you make it stop by doing something about the situation (either removing some files or asking for a larger quota).

    In a bit more detail: We have things set up so that once a week the system checks all user quotas and sends warning messages to users who are over quota. Our thinking is that users who go over quota will therefore find out about it before the end of grace period and be able to take appropriate action before the system's enforcement mechanism kicks in. Copies of the messages also go to one of the sysadmins, who has been known to take action and/or send follow-up messages. The messages' ``reply-to'' address is set to send to her as well.

  3. What happens if I go over quota and do nothing?

    Maybe nothing; if nothing you do with your account runs up against the system's quota enforcement mechanism, everything may seem fine (except of course that those warning messages keep going out). But if you do anything that does run up against the enforcement mechanism, odds are you'll notice: Ill effects can range from sluggish logins/logouts to losing work when you open a file in a text editor and try to save it. (``The computer ate my homework!'') ``Are you over quota?'' is one of first questions in troubleshooting otherwise mysterious problems with students' accounts.

  4. How can I be over quota? All I have is a few files for my classes!

    You might be surprised how much space some applications use for hidden files (ones whose path names start with a ``.''). Browsers cache previously-fetched pages, GUI applications store configuration and history information, etc., etc.

  5. How do I find out what's taking up so much space?

    Some command-line tools that may be helpful:

    Some typical space hogs:

  6. Okay, I know what's taking up space. Now what?

    If it's a hidden directory associated with a GUI application, it's probably safest to remove files using the application itself:

    Otherwise you can use either the graphical file manager or command-line tools to remove unneeded files:

    If you do the above and are still over quota, talk to someone in the department (course instructor, research supervisor, one of the admins) about an increase in quota. Reasonable requests for a larger quota are usually honored.

  7. Why do you impose quotas anyway? Disk space is cheap!

    Yes, it is, and ITS has been generous in providing us with a lot of it. But it's a shared resource, and you've probably all noticed that today's ``more than anyone could ever use!'' is tomorrow's ``barely enough'', and if we take no steps to limit anyone's use of this shared resource, the result is that it fills up and no one can get much done.

Complete text of the sorted-disk-usage script:

# show disk usage of directory and all files/subdirectories, sorted 
# by size in ascending order.  
# usage:  sorted-disk-usage directory
if [ -z "$1" ]
	echo usage is `basename $0` directory
	exit 1

find "$1" -mindepth 1 -maxdepth 1 -exec du -sk {} \; | sort -n

echo ""
echo "total:"
du -sk "$1"

Berna Massingill