Is there a way to filter site categories for Ubuntu 11.04 just like SelfControl so that I won't be able to pass them i.e, gain access to them by turning something off (for unlimited time)?
You can search your browser for parental control plugins.
This link will take you to the list of parental control plugins for Firefox
This link will take you to the list of parental control apps/extensions for Chrome at the ChromeWebStore
The easiest way to "turn something off" would be to add a domain name to /etc/hosts and point it to a wrong IP address (127.0.0.1 would do)
Coincidentally, you need sudo access to edit that file, so if you edit it and then ask another admin user on the same machine to revoke your sudo rights - you will be unable to access those domains.
This solution, of course, is very basic. If you want something more complex you can install DansGuardian or other filtering software.
Anyway, the key aspect is to relegate your root access - with root access there's nothing you can't disable on the machine (unless, of course, if you can set up your local network so all traffic goes through another locked-down machine which runs filtering software in transparent proxy mode).
UPDATE: It dawned on me that "self control" in the question title means "SelfControl application for MacOSX", not an act of somebody controlling themselves :) Well, I'm finding their claim that it can't be turned off implausible, provided the person has root access to the system.
However, there seem to be a Linux port of the application: SelfControl -- The Linux port - though, again, it doesn't (and can't) prevent somebody knowledgeable with root access from disabling/reverting the block.
UPDATE2: Actually, if you have a look at SelfControl's source code, you'll find that it blocks sites by adding an entry to
/etc/hosts, just as I suggested in the beginning :) My understanding is that Linix version uses iptables for that, which is kinda a bit more sophisticated but still is far from "impossible to turn off"
There appears to be a SelfControl port to Linux here: http://svn.jklmnop.net/projects/SelfControl.html