I want all the apps to be installed in /home directory. Is it possible?
Yes. But you need to install software from SOURCE not from the software center. Before you start thinking about doing that please keep reading.
The free space available in usr/lib directory is around 12GB, which I don't feel is enough for me. Is it possible to change to /home directory?
Beside leaving the installation method Ubuntu uses by default... there are other options ...
If you do not use hibernate and have a largish amount of money you can free up space by deleting swap. You can also resize /home and "/" by moving a bit from /home/ to "/". You can make a separate partition of /usr/ or /var/ by splitting /home/ into 2 partitions and mounting that other directory in the empty one.
And the is not even mentioning the more simple option of adding a extra hard disk to a desktop.
The question you need to answer: if you have a 17Gb "/" and you now have still 12 Gb free ... What are you planning to install to fill up that 12Gb?! And if you can answer that: you believe you need ALL those 12Gb worth of software at the same time?
My personal partitoning:
rinzwind@schijfwereld:~$ df -H
Filesystem Size Used Avail Use% Mounted on
/dev/sda5 99G 7,2G 87G 8% /
/dev/sdb5 25G 2,2G 22G 10% /home
/dev/sdb6 365G 174G 173G 51% /discworld
I have 2 disks in my notebook (the 99G one is an SSD). And I have MySQL running on this machine (as with all personal data: the SQL database file is on /discworld/). I have never ever been over 10Gb Used the whole time using Ubuntu. And my /home/ never ever got over 3Gb Used.
No you'll be fine with your current setup. I would start to worry when your "/" is filled up 90+%. Not sooner.