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Topic: understanding OpenWrt

The content of this topic has been archived on 13 Apr 2018. There are no obvious gaps in this topic, but there may still be some posts missing at the end.

I'm trying to understand to some level the inner workings of OpenWrt. As I own Zyxel P2812HNU-F1 I will be reffering to wiki for this router.

On my desktop Linux I can see that grub config has two entries: one specifying kernel file and another specifying initramfs file:

root (hd0,0)
kernel /boot/vmlinuz-2.6.32-504.16.2.el6.x86_64 ...
initrd /boot/initramfs-2.6.32-504.16.2.el6.x86_64.img

Wiki for P2812HNU-F1 says that during flashing process kernel file is uploaded into RAM memory:

tftp 0x80800000 openwrt-lantiq-xrx200-P2812HNUF1-uImage

then it is written to NAND:

nand write 0x80800000 0x60000 0x200000

then a separate file openwrt-lantiq-xrx200-P2812HNUF1-uImage-initramfs is loaded into RAM and run:

tftpboot 0x80800000 openwrt-lantiq-xrx200-P2812HNUF1-uImage-initramfs
bootm 0x80800000

1) my understanding is that this second file is -- by analogy with my linux desktop -- actual kernel + initramfs file, like two-in-one. is this correct?

2) only kernel file is written into NAND (openwrt-lantiq-xrx200-P2812HNUF1-uImage). so when next time the system boots up it is missing initramfs file (if my understanding is correct of course). is this so? does the kernel file (openwrt-lantiq-xrx200-P2812HNUF1-uImage) have everything it needs (compiled inside openwrt-lantiq-xrx200-P2812HNUF1-uImage) and doesn't require separate initramfs file?

I would appreciate your answer.

thank you,
geos

(Last edited by geos on 30 Jul 2015, 17:59)

No, yhe initramfs means "a file for start from ram" in desktop with no space limit is the standard way, in tyny devices no. in this case "uimage" is a special file format to be started by uboot, and the initramfs is for start from ram, not from flash. useful if you want to delete, write ... flash.

and yes, the flashed kernel dont use initramfs,.

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