What is the command used by sysadmin to see the disk used by the users in descending order of their disk usage?

You could use a du on all the /home subdirectories (or where their home directories are located):

cd /home
du -k -s * | sort -k1 -g -r

On Soalris, the above command gives error. Can u let me know where the problem is. Thanks

What error does it give you?

It gives error with -g option. It says illegal option -g. when i tried without -g option it worked. but it was not in asending order of use.

The -g option stands for a numeric sort. It works in Linux, possibly the Solaris 'sort' has different options. Check with man sort which option matches a numeric sort in Solaris and use that.

The -r option is for reverse order. Again this might be different in Solaris.

with a little help from the sort man page

OS: solaris
Ver: 7
Hardware: ultra 5

for i in `awk -F":" '{ print $1 }' /etc/passwd`;do
du -s `find . -user $i`|sort -nr
done