Nexus S : Root Ice Cream Sandwich after upgrade from Gingerbread

Assumptions being made here:

1. You have ClockworkMod's ROM Manager installed.
2. You installed ICS 4 .
3. You have Android SDK installed.
4. You have a fastboot program and have set up the USB rules on Ubuntu (see earlier posts).
5. You have a custom recovery image such as ClockworkMod.
6. You have a copy of the superuser program in ZIP format installed on the root of your SDCard.

Procedure:

1. Put the phone into the bootloader - power off, power on whilst pressing volume up. Or use adb:
   
   adb boot bootloader
   
   Either way when it is in the bootloader, confirm your connected properly:
   
   fastboot devices
   
   Which *should* list your device else review the settings in the earlier post.
2. Run fastboot to boot the recovery image:
   
   fastboot boot path to recovery image
3. Phone will boot to the recovery image.
4. Use the recovery image tool to locate the superuser zip and install it.
5. Boot phone and enter ClockworkMod ROM Manager to re-flash the recovery image to make it permanent. If you do not have ROM Manager, refer to the earlier post on making the recovery image permanent.