It looks like DB2 wants to install to /opt by default. According to your df output, /opt should be located on /dev/hda5, which does not have enough space (190MB where you need at least ~540, plus space for your data).
I would recommend installing to /usr, as this is located on a different partition (which has 17 Gigs available). As I don't know DB2 specifically, you will need to check the documentation for how to change the install directory.
Alternatively, you could try using symbolic links from /opt to /usr, but I think that will get a bit messier.
Hope this helps!
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