[gentoo-user] HACK: Boot without an initramfs / initrd while maintaining a separate /usr file system.

[Grant Taylor]

On 8/4/19 7:26 PM, Grant Taylor wrote:
> I am also using a bit of a hack that I think could be (re)used to allow
> /usr being a separate file system without /requiring/ an initramfs /
> initrd.  (I'll reply in another email with details to avoid polluting
> this thread.)

I think that a variation of a technique I'm using for LUKS encrypted 
/home on a VPS could be used to allow booting without an initramfs / 
initrd while maintaining a separate /usr file system.

The problem is that /bin & /sbin would be symbolic links to /usr/bin & 
/usr/sbin.  So, any commands that would be needed to mount the /usr file 
system would need to be directly accessible in /bin & /sbin paths, or 
indirectly accessible in /usr/bin & /usr/sbin.

IMHO this is a whopper of a hack.

Create the bin and sbin directories inside of the /usr directory that is 
the mount point so that they are on the underlying file system that /usr 
is mounted over top of.  Then copy the needed binaries to the /usr/bin & 
/usr/sbin directories on the underlying file system.  That way, 
/sbin/fsck -> /usr/sbin/fsck still exists even before the real /usr is 
mounted.

I did say this is a whopper of a hack.

It's trivial to access these directories even when the normal / full 
/usr is mounted.

1)  mkdir /mnt/root-underlay
2)  mount -o bind / /mnt/root-underlay
3)  ls /mnt/root-underlay/bin /mnt/root-underlay/sbin

This "technique" / "trick" / "hack" works because the /bin & /sbin 
""directories are sym-links to the /usr/bin & /usr/sbin directories. 
There is nothing that means that the contents of (/usr)/(s)bin can't 
change from one command invocation to another.  The /(s)bin sym-links 
just need to point to a valid directory.  They can easily be on the 
root-underlay file system that /usr gets mounted on top of.



-- 
Grant. . . .
unix || die