I want to set home directory limit of 10GB for all users in Ubuntu. Can anyone tell me how could I do that?
For clarification, do you want your home directory in total to have a 10GB limit? Or do you require each user individually to have a 10G limit for their respective home directories?
Some how-to's which should help you with both scenarios:
Debian, quick rundown: http://www.howtoforge.com/how-to-set-up-journaled-quota-on-debian-lenny
Centos based, but thorough clear and easy to follow http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-disk-quotas.html