Is it possible to mount overlay on initramfs?

[Psychesnet]

Hi all,

At OpenWrt 22.03.x, is it possible to mount overlay on initramfs?
I asked the question with chatGPT, I try the script and it is not working.
I try to use procd to auto mount overlay, but the log show

[   12.249624] block: attempting to load /tmp/ubifs_cfg/upper/etc/config/fstab
[   12.256895] block: unable to load configuration (fstab: Entry not found)
[   12.263911] block: attempting to load /tmp/ubifs_cfg/etc/config/fstab
[   12.270756] block: unable to load configuration (fstab: Entry not found)
[   12.277655] block: attempting to load /etc/config/fstab
[   12.283856] block: extroot: not configured
[   12.290334] mount_root: switching to ubifs overlay
[   12.301604] mount_root: pivot_root failed /mnt /mnt/rom: Invalid argument
[   12.308738] mount_root: switching to ubifs failed - fallback to ramoverlay
[   12.316213] mount_root: opening /proc/filesystems failed: No such file or directory
[   12.324139] mount_root: BUG: no suitable fs found

Anyone can help? Thanks.

[slh]

A note about using ChatGPT for OpenWrt Answers

I want to make it clear: ChatGPT is not an authoritative source for information about OpenWrt or networking in general (among many other topics). The AI systems currently create human-sounding answers, and they pull from various sources on the internet. The problem is that they do not have any mechanisms to ensure the accuracy of the responses, nor do they provide context as to how they arrived at the answer. Please do not post the ChatGPT ‘conversations’ or ‘solutions’ here, as they are more …

[Psychesnet]

Something from Google, still not working.

mount -n -t ubifs ubi0_0 /overlay 
mount -n -t overlay overlayfs:/overlay -o rw,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work /mnt 
mount -n /proc -o noatime,--move /mnt/proc 
pivot_root /mnt /mnt/rom  
mount -n /rom/dev -o noatime,--move /dev 
mount -n /rom/tmp -o noatime,--move /tmp 
mount -n /rom/sys -o noatime,--move /sys 
mount -n /rom/overlay -o noatime,--move /overlay 

The error is

root@53a6:~# pivot_root /mnt /mnt/rom  
pivot_root: (null): Invalid argument

[Mijzelf]

From man pivot_root:

The rootfs (initial ramfs) cannot be pivot_root()ed. The recommended method of changing the root filesystem in this case is to delete everything in rootfs, overmount rootfs with the new root, attach stdin/stdout/stderr to the new /dev/console, and exec the new init(1). Helper programs for this process exist; see switch_root(8).

So AFAICS your only option is to copy the content of the initramfs to a newly mounted tmpfs, and use that to create a layered filesystem. Then you can pivot_root or chroot into it. But the old initramfs keeps in memory. The alternative is to do from init, in process 1, then you can switch_root to the new filesystem, destroying the old one.

[Psychesnet]

Thanks @Mijzelf , looks like I need to change my way to create rootfs.