Disk Quotas for UNIX & mail inbox files

LAST EDIT: 28 Cheshvan 5759, 17 Nov 1998, by Haim Roman.

CONTENTS:

WHAT ARE QUOTAS, AND WHAT ARE THE POLICIES?
CHECKING YOUR USAGE AND QUOTA
CLEANING YOUR FILES
MORE INFORMATION

1. WHAT ARE QUOTAS, AND WHAT ARE THE POLICIES?

1.1. Introduction

A disk quota is simply a limit on how much disk space you can use. Without quotas, some users would use so much disk space that they would fill up the disk. When this happens other users cannot work.

In UNIX, there are actually 2 types of quotas:

quota, or soft limit: This is the amount of disk space that you are allowed to use. However, you are allowed to use more than this for a short period of time. This allows you more flexibility when you need to use a lot of disk space in temporary files.
limit, or hard limit: You are not allowed to use more than this, even for a second.

1.2. Our Policy

The current policy is to grant each user a quota of 16 megabytes (MB). In addition, the user is allowed up to 5 megabytes for his/her mail inbox file. If you feel that you need more, please send mail to 'problems' (see below for more information on this address). Please state how much you think you need, and why. If you are a student, your instructor or project advisor should also send us a note authorizing your request.

2. CHECKING YOUR USAGE AND QUOTA

To see if you are over your quota, simply type the command quota. To get more information, type quota -v. The "-v" option means verbose; that is, it gives more information. Here is a sample of its output:

Filesystem     usage  quota  limit    timeleft  files  quota  limit    timeleft
/var/spool/mail   62   8000  18000                 21      0      0            
/usr/u             0     10   1000                  0      0      0            
/usr/u2            0     10   1000                  0      0      0            
/usr/u1            0     10   1000                  0      0      0            
/remote/makot/opt  0     10   1000                  0      0      0            
/usr/local/etc     0     10   1000                  0      0      0

Here are the meanings of the columns:

Filesystem: A section of a disk. If the filesystem containing your home directory fills up, then you cannot write any files. It does not help if other filesystems on the same disk have room.
usage: How much disk space your are using. The number is in units of kilobytes (1 kilobyte = 1024 bytes). Divde this number by 1000 to get the approximate number of megabytes.
quota: I.e, the soft limit. This column is also in kilobytes. 0 means no quota.
limit: I.e., the hard limit. This column is also in kilobytes. 0 means no quota.
timeleft: if you are over your quota, this is the amount of time the system gives you to delete files so that you are under your quota. If you remain over your quota after this time, you will not be able to write any more files.
files: Besides quotas on the amount of disk space, we can also set quotas on the number of files you are allowed to have. This column shows how many files you have.
quota, limit, & timeleft: Similar to above, but relevant to number of files.

Unfortunately, the output of quota -v can be confusing, because it gives you a lot of irrelevant information. You can ignore the following data:

Any row that has a very small quota. That means that you probably do not files in that filesystem.
The 'files' column and all columns to the right of it.

3. CLEANING YOUR FILES

3.1. Deleting

One way to clean up your home directory is to delete files. Use the rm -i command to delete. 'rm' stands for 'remove'. '-i' stands for interactive; before deleting each file, the system asks you if you really want to delete it.

To delete an entire subdirectory, you can use rm -ri. The additional 'r' means 'recursive'; it deletes all files under a given directory.

You probably want to delete any files whose names end with '~' or whose name is 'core'. The emacs saves backups of files it edits; the name of the backup is the name of the file with the '~' appended to the end. Thus, if you editing a file named 'foo', emacs will create a file called 'foo~'. If a program crashes, the state of the program is saved in a file named 'core' (that is why this is called dumping core). You only need the core file for debugging. In fact, you can prevent the core file from being created in the first place by running the command limit coredumpsize 0. Put this command in the '.cshrc. file in your home directory.

WARNING: if you accidentally erase files that you really want to save, we might not be able to restore them soon. Be careful!

3.2. Compressing

For files that you want to save, but do not use much now, you should compress them. For this, use the command gzip. To compress all files within a directory (say the directory is called 'foo'), run gzip -r foo. As with the rm command, '-r' means 'recursive'.

You can uncompress files with the gunzip command. As with gzip, it also takes the '-r' option.

3.3. Mail Inbox

You should not leave old messages in your mail inbox. That could cause the mail inbox to grow quite large. You should either delete a message after you read it, or save it in a different folder.

4. MORE INFORMATION

You can get more information about the above commands via the man command. You can access a web-interface to the man command, as well as other information from the Computer Center home page.

You can also send mail to problems. A copy of this mail gets sent to almost all members of the Computer Center, and is thus usually better than sending mail to specific staff members.