Out of Disk Space - MAC

First, make sure you are emptying the trash, not just putting things in the trash.  One way to do this is to select Empty Trash from the Finder menu.

Second, create a smart folder that sorts everything on your harddrive by size.
 - Go to the Finder and from the File menu select New Smart Folder
 - Delete one of the two conditions by clicking on its minus button.
 - Change the remaining condition to Size and Greater Than.  Put in a large quantity like 1 MB to limit the search results.
 - Once you get the results, change to list view and then sort on size so you can see the largest files on the drive.

Ooops.  Disregard the second part.  Smart folder's weren't introduced until 10.4.  Step 1.5 - Install Tiger.  Of course, you can't because there isn't enough room.

In your search for large culprits, make sure you have folder size being shown:
 - Open a Finder window
 - Select List View
 - From the View menu, select Show View Options
 - Check Calculate all sizes

Now, sort by size and drill down to find your large files.

There is a nice visual FREE tool called Disk Inventory X - http://www.derlien.com which will show you all the files on the Mac, colour-coded and organised by size.
The other great utility is called WhatSize - http://www.id-design.com/software/whatsize/index.php

This web page has some other tips about saving space ... http://www.thexlab.com/faqs/freeingspace.html

I used to run into an issue with Jaguar (10.2) where temp files were being created in the invisible directories when a program would crash. These files should be deleted after a reboot, but that didn't always happen. The nature of the work I did on the computer meant that I regularly had large files (~1GB) open which created at least that large of a temp file that wouldn't delete. Over time, these obviously piled up and filled the machine. I eventually realized this by doing a search through the invisible directories. You can possibly find them by going to the Menu and selecting File | Find and change the options to show invisible items.

Another possibility is that the drive is just completely full. I have taken care of a computer lab where video was constantly being stored and edited on the computers. It's amazing how much storage can be taken up by raw video. An hour and a half movie can be 50GB uncompressed.

What is the function of the Mac? Large graphics file editing, video editing, anything like that?

all great options have been mentioned.

however, you didn't specify what program or what you were doing when you get the disk full error. just to cover another base, if you are getting the disk full error from ms word you might try this workaround:
http://word.mvps.org/Mac/DiskFullError.html

i've been trying to squash the disk full error from word for a while, so thought i'd add my 2¢

The disk is full - there is only 200 MB of free space on a 149 GB hard drive.  The user is a designer - we have removed all her files to an external drive.  Are there any hidden tmp files or such that could be causing the problem.  About 3 weeks ago she had 30 gig free.

Download and run MacJanitor:  http://www.versiontracker.com/dyn/moreinfo/macosx/10491 which will clean out old log files.

Then run Onyx: http://www.titanium.free.fr/pgs2/english/onyx.html to clear caches.

Both products are freeware.

Also see this link:  http://www.macfixit.com/article.php?story=20061226062915725&query=full+disk

Apple made a change where /var/tmp used to be removed and
 recreated on reboot by /etc/rc. Now only "/var/tmp/folders.*" is
deleted.

You can goto the Main menu and select "Go | Goto Folder" and then type /var/tmp

This will take you into the /var/tmp directory and you can delete anything in there that is wasted space. You may want to use the command line to do this if you are comfortable enough at it.

In terminal:
login as sudo
cd /private/var/tmp
rm *.*

Reboot.

I deleted the contents of /var/tmp.  At the time the user was down to 50MB of free space.  This got her to about 350MB.  I just checked in with her - she is down to 290.  
What could the problem be?  I need to upgrade her to Tiger but can't with this problem.

There are clearly large or many files on the Mac that are using the space.  If you cleared the TMP folder and rebooted all the likely cache and temp files have been removed.  There is not much more you can do to remove temporary files so it looks like these are files that the user created intentionally.
Have you run all the maintenance scripts which remove and clean log files etc?

1. Launch Terminal, in the Macintosh HD > Applications > Utilities folder.
2. At the Terminal prompt, type the following, exactly as written:
sudo periodic daily weekly monthly
3. Press Return.
4. Type your Admin password when prompted, then press Return.

Were they using iDVD or iMovie?? These can rapidly create GBs of data imporing movie files.

Did you use Disk Inventory X and What Size to sort the whole Hard Disk by File Size and see what the biggest files are?
For example see how big the Users Home Folder is .. i.e. /users/XXX (where XXX is their username)
Then look inside the Documents/Pictures/Movies folders .. to see how big they are. If one is taking up 10s of GBs ... drill down to see where the culprits lie.

I have seen the situation where a laptop user accidentally dragged their system folder and dropped it onto their Documents folder thereby creating a FULL copy of their SYSTEM INSIDE their Documents folder .. instantly losing 5Gb of space.

Assuming that you have rebooted lately? I know, sounds like a trivial question, but I have some across people that don't reboot, but once a month or two and the paging file becomes majorly bloated.

Another trick to try:
Assuming you have a single, large file taking up space somewhere (which may or may not be the issue), goto the main Finder menu, Select File | Find. Then choose size greater than 500MB or whatever size files you want to search for. You might find a surprise somewhere in the hard drive. Unfortunately, this won't find files in the invisible folders. I think you can do it using command line (in terminal, type man find for instructions).

The user shuts down the MAC everynight.  
Within a month the disk space went from 30GB to 300MB.  
The user is out on Monday.  My plan is to install Tiger - I have a "clean" MAC that I will use for the Migration Assistant so that I can bring over her files and applications.  Any chance the "problem" will remain?

You could do a search for all files modified in the past day, however, again this search would not find files located in the private (invisible) directories.

How do I find the files in the "invisible" directories.  Based on the size of the visible files, that is where the problem is.

This free utility will toggle visibility off and on:

http://www.versiontracker.com/dyn/moreinfo/macosx/14722

ok, here we go....

I'm sure it can be done through terminal (command line) but I haven't done it in awhile and don't feel like reading a reaaaaaaally long man page.

I'd enable root if you haven't already. This can be done in Netinfo manager under security. Then login as root with the password you gave it.

Then, goto the Finder menu, select Go | Go to Folder and type in /private
In the window that opens, are some (not all of the) invisible folders. You can also type in /usr or /bin or /dev for others, but BE WARNED!!!! You are monkeying with the Operating system and can do MAJOR DAMAGE. I would not delete anything other than possibly items in a tmp folder. You should make sure you have a backup of anything important before you even begin this.

You can then select folders and do a 'get info' to determine which are larger and try to narrow down where your 800 lb. gorilla lives.

The main reason for doing the steps above are to try and find what large files you may have. Again, I would NOT DELETE anything just hoping and guessing it might be the issue.

Good Luck.

The WhatSize tool shows ALL files including "invisible system files" .. there's no need to go switching invisibility on or off.

Starting at the root level / view folders by size .. see which are the biggest and then drill down.

If you find large files, send us the names and sizes if you are unsure about deleting them.

If you are comfortable in Terminal, the following command will find all files greater that 100 MB (alter number to control size of search).

mdfind 'kMDItemFSSize > 100000000'

Thank you all for the suggestions.
Yesterday morning she was down to 8MB of free space
I migrated her settings, applications, etc  to another MAC.  Installed Tiger (formatted drive) on her MAC.  I then migrated her settings, applications back.  The user now has 122GB of free space - I still wish I knew what the issue was.  Based on this, this question can be closed.