[U-Boot-Users] where is the process counter when the linux system shutdown

I want to update the system which included kernel and filesystem via internet. Now ,tow question will be solved.

the first: how to get the kernel or filesystem from long-distance host(not in LAN ) . I want to migrate a ftp tool into U-boot at one time.but it seems so hard and I' m not good at program in U-boot.

maybe.I can get the kernel or filesystem before boot the system.and write the data into RAM.

the second:

how do I copy the RAM data to ROM(nand flash).can I write the data in linux system if can not do this . I need shutdown the OS and run a nand flash write program. well ,where is the process counter when the linux system shutdown. and how to call the nand flash writer.

any advice will be appreciate.