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We didn't exactly expect it to take long, but the Nexus S that went on sale today has now been rooted by Koush, the creator of ClockworkMod recovery and ROM Manager. ROM Manager support is coming very soon, but in the meantime, you can get your Nexus S rooted and ClockworkMod installed by following these easy instructions, courtesy of Koush:

Step 1

First, reboot into your bootloader/fastboot mode. (Volume + Power Up, or adb reboot bootloader)

fastboot oem unlock

Step 2

Then, install ClockworkMod recovery, crafted specifically for the Nexus S:

fastboot flash recovery recovery-clockwork-herring.img

Step 3

Boot into Clockwork recovery and install the Superuser zip file (adb reboot recovery, or from fastboot choose recovery).

There you go, now you are rooted - these dev-friendly, easily unlockable phones simply rock, don't they?

Source: Koush @ xda