If you type #df –k and notice that %Used is fairly high (88% and above), here are some commands to use to look for the largest culprits.
#df –kFilesystem 1024-blocks Free %Used Iused %Iused Mounted on
/dev/hd4 327680 87472 74% 2493 2% /
/dev/hd2 1900544 131008 94% 46971 10% /usr
/dev/hd9var 131072 98292 26% 1003 4% /var
/dev/hd3 6881285 13644 26% 2781 2% /tmp
/dev/hd1 163840 33740 80% 3022 8% /home
/dev/udthome 720896 75336 90% 21385 12% /usr/udthome
/dev/ud 6553600 2068464 69% 7694 6% /ud
Notice that /usr is 94%. First check for the largest directories in that path.

# cd /usr
# du –sk * sort –n The output is in reverse order and shows the directories in /usr that contain the largest amount of data.
254636 lpp
308420 lib
375648 vsifax3
613296 udthome
We ignore udthome; it is its own filesystem as shown in the df –k output, /usr/vsifax is the next highest.

# cd /ud/vsifax3
# du –sk *
You do this for each sub-directory until you get to the one with the largest amount of data.

Now you want to check for the largest files in that directory….

# cd /usr/vsifax3/lib>
#/usr/vsifax3/lib>ls -la sort +4rn | head
This shows, by default, the 10 largest files, add –15 after head to get more.

-rw-r--r-- 1 vsifax vsifax 230102 Apr 12 4 vtermcap.old In this case vtermcap.old is an old big file that can probably be removed.
-rw-r--r-- 1 vsifax vsifax 30102 Oct 31 13:34 vtermcap
-rw-r--r-- 1 vsifax vsifax 10731 Oct 31 13:34 license.txt
-rw-r--r-- 1 vsifax vsifax 9756 Oct 31 13:34 c2modems.new
-rw-rw-r-- 1 vsifax vsifax 9756 Jun 20 10:02 c2modems.ini
-rw-rw-r-- 1 vsifax vsifax 7281 Jul 12 13:26 dialcode.lst
-rw-r--r-- 1 vsifax vsifax 7261 Oct 31 13:34 dialcode.new
-rw-r--r-- 1 vsifax vsifax 4402 Oct 31 13:34 vsi.res
-rw-r--r-- 1 vsifax vsifax 2594 Oct 31 13:34 crontab.new
drwxr-xr-x 2 vsifax vsifax 2048 Oct 3 10:50 fxpcl

Another way is to check for files over a certain amount…

# /usr/vsifax3/lib>find . –size +10000 –print –exec ls –la {} \; > /tmp/big.files

This places a list of files over 10M in /tmp/big.files
To narrow down the list, alter the 10000 to be lower or higher.
# more /tmp/big.files
-rwxr-xr-x 1 vsifax vsifax 11402864 Oct 31 13:34
./ghostscript/bin/gs./xmlf/api/docs/xmlf-api.doc
-rw-r--r-- 1 vsifax vsifax 13152704 Oct 24 09:56
./xmlf/api/docs/xmlf-api.doc./xmlf/api/java/swingall.jar
-rw-r--r-- 1 vsifax vsifax 21396234 Oct 24 09:56 ./xmlf/api/java/swingall.jar