How to find a file or files using maximum space on Unix Systems like Solaris , Linux, HP-UX or AIX?

Example For Finding out the file bigger than 100MB

find /var -xdev -size +100000000c -exec ls -lh {} \;

-xdev is being used so that you can find out the file in the filesystem where /var is located. Many times we have other filesystems as well part of /var like /var/crash(which is mounted from a another Filesystem) . 

So, my advice is to always xdev to ensure that you are searching in the right directory.