How do you jailbreak ipod touch 4.2.1?

Limera1n or the revolutionary permanent jailbreak Greenp0ison, it depends on what model iPod you have for example; you cannot jailbreak a 2nd generation MC model until a further update is released. Limera1n is buggy and is not recommended but if greenp0ison doesn't work, it is your only alternative. Beware of imitations that contain viruses. A permanent jailbreak is a jailbreak that won't break if you update your ipod's software. Both jailbreaks are tethered meaning that your ipod has to be connected to a computer. google limera1n and greenp0sion and make sure you have the right links. They are both case-sensitive and i would recommend greenp0sion. Hope this information helps.