What is a good lag-free screen recorder for Linux?

I want to be able to record minecraft so I can get video evidence to ban hackers for a server (us.thedarkage.nl), but every time I've tried one my gameplay becomes choppy, which would make it difficult to catch a hacker or actually be able to see if they're hacking. Does anybody know of a good one compatible with linux? (OS is Ubuntu)

For a start, I would recommend you stop using Ubuntu, There are better faster Linux distributions available here are some of them. You should always ask questions at the linux your using forums then you'll get the right answers,
http://zorin-os.com/free8.html/
http://linuxmint.com/...xmint.com/
Zorin users forum website
http://www.zoringroup.com/forum/viewforum.php?f=3
Mint users forum website
http://forums.linuxmint.com/