Check your /etc/mtab on the failing system to see how the kernel believes the
root partition has been mounted.
I ended up including a fix-up in at the end of my init script to ensure
/etc/mtab correctly reflected my aufs root file system
# Insert our new root into the mtab
sed -i '1i none / aufs dirs=/rw=rw:/ro=ro' ${NEW_ROOT}/etc/mtab
this is performed just before performing the “switch_root” process.
Also are you sure "/etc/initramfs.mounts" is actually being processed?
If you are passing the “aufs” option into the init script using grub then the
code to process "/etc/initramfs.mounts" is never called.
It’s been a few years since I set this up but like you I use genkernel to
create the initramfs (yes I’m lazy). However I replace the default genkernel
init script with a slightly modified version using the ‘--linuxrc’ option. This
replacement script includes my additional aufs mounts and manages a few
additional functions such as performing software updates which for obvious
reasons can’t take place on a fully running system.
I use the ‘loop’, ‘looptype’, ‘ramdisk’ and ‘aufs’ init options which are
passed in via the grub boot manager. These options are normally used for live
CD builds to overlay a small ram disc on top of the CD using aufs. In essence
my change simply maps another physical partition over the top to allow for
permanent data storage.
Gareth.
From: Francisco Ares [mailto:[email protected]]
Sent: 18 October 2013 18:16
To: [email protected]
Subject: Re: [gentoo-embedded] planning a flash DOM x86 embedded system
Thanks, Gareth.
But it is very interesting that with no special customizations, I am almost
able to have a fully functional system.
That new thing about having to use a initramfs when the root filesystem and the
/usr directory are not present in the same physical partition, it turns out
that it helps on having the "genkernel" generated initramfs do the job of
mounting different arrangements for partitions, directories and unionfs mounts.
That is because of the file "/etc/initramfs.mounts" where the specified mount
entries, are extracted from the "/etc/fstab" and mounted before the initram
gives way to the real root environment.
For instance, in this system, for now, there is the directory structure bellow:
/.var.rw - here a r/w ext4 partition is to be mounted;
/.var.ro - here there are all files and directories expected to be on a usual
/var;
/var - here a unionfs mount is to join the ones above
The part from fstab for this is ("/.var.ro" is present on the squashfs root
file system):
/dev/sda2 / squashfs noatime,ro
0 1
/dev/sda3 /.var.rw ext4
noatime,defaults 0 2
none /var unionfs
nonempty,cow,umask=022,dirs=/.var.rw/=rw:/.var.ro/=ro 0 0
I said it is not yet fully functional because it seems there is something wrong
with permissions, because it ends up with a unknown user prompt from which I
could list the root directories (something similar is being made to "/etc"):
total 9,0K
drwxr-xr-x 23 root root 385 Out 18 14:18 ./
drwxr-xr-x 4 root root 4,0K Set 24 09:46 ../
drwxr-xr-x 47 root root 2,6K Out 17 16:03 .etc.ro/
drwxr-xr-x 2 root root 40 Out 18 15:09 .etc.rw/
drwxr-xr-x 11 root root 262 Out 17 16:03 .var.ro/
drwxr-xr-x 6 root root 4,0K Out 18 14:33 .var.rw/
drwxr-xr-x 2 root root 1,4K Out 7 14:46 bin/
drwxr-xr-x 4 root root 1,0K Out 18 14:15 boot/
d????????? 3 root root 2,3K Ago 1 00:17 dev/
drwxr-xr-x 1 root root 2,6K Out 17 16:03 etc/
drwxr-xr-x 3 root root 54 Ago 22 07:55 home/
lrwxrwxrwx 1 root root 5 Out 7 14:05 lib -> lib64/
drwxr-xr-x 12 root root 3,2K Out 17 08:51 lib64/
drwxr-xr-x 2 root root 28 Ago 1 00:16 media/
drwxr-xr-x 2 root root 28 Ago 1 00:16 opt/
drwxr-xr-x 2 root root 3 Jul 31 22:22 proc/
drwxr-xr-x 2 root root 136 Out 18 14:18 root/
drwxr-xr-x 5 root root 120 Ago 30 08:59 run/
drwxr-xr-x 2 root root 2,9K Out 17 08:51 sbin/
drwxr-xr-x 2 root root 28 Ago 1 00:16 sys/
drwxrwxrwt 2 root root 3 Out 18 14:18 tmp/
drwxr-xr-x 13 root root 267 Out 17 11:18 usr/
d????????? 1 root root 262 Out 17 16:03 var/
Any hints or suggestions? I will post this to the "gentoo-user" list, also, I
guess it is an interesting thing that might be called a cool side effect of the
recent issues.
Thanks
Francisco
2013/10/17 Gareth McClean <[email protected]>
I do this using a slightly modified init script, aufs3 and a squashfs.
Basically the system setups a tmpfs as a RW overlay on top of the squashfs.
Then for permanent storage there is a physical Ext4 partition overlaid again on
top of the /home directory.
Symbolic links are then used for any configuration files (such as network
configuration) that require persistent storage. These links obviously reference
locations within the /home directory that is stored on an Ext4 physical
partition.
My init script is slightly more complicated than this since it caters for both
live (squash plus aufs) and development (normal disc access) modes but
basically it boils down to:
mount -t aufs aufs "${NEW_ROOT}" -o dirs=/rw=rw:/ro=rr
# Mount RW_PERM
echo "Mounting RW"
mkdir -p /rw-perm
mount "UUID=${RW_PERM_UUID}" /rw-perm
mount -o bind /ro/home "${NEW_ROOT}/home"
mount -t aufs aufs "${NEW_ROOT}/home" -o dirs=/rw-perm=rw:/ro/home=rr
where
ro = squashfs
rw = tmpfs
rw-perm = physical Ext4 partition
Note you need the “mount -o bind" command to allow an overlay on top of an
overlay with aufs3 otherwise you will get an error message.
BTW, Unless you have a good reason for doing this I would not recommend doing
this since you have a physical hard drive. The reason I still do this is mainly
for backward compatibility. Of course it is nice to have the ability to run our
system from a liveUSB stick and it minimises software download size when doing
updates but debugging the init script is a very time consuming process……
From: Francisco Ares [mailto:[email protected]]
Sent: 16 October 2013 13:49
To: [email protected]
Subject: [gentoo-embedded] planning a flash DOM x86 embedded system
Hi.
I am planning to build a system to be deployed in a SATA flash disk, and most
of the file system will be read-only. There will be a tempfs on /temp and a
read-write partition for /var (perhaps a unionfs with the static part of /var
and that read-write partition)
Is there any resources on how to do this using Gentoo?
There is already a development system with everything working as expected on
the final system. But when I put it to a squashfs, the system boots with
several errors, like when trying to write to /etc and /var.
Looking on the new issue regarding /usr and / being on a different partitions,
I have found the file in /etc/initramfs.mounts. I have added the needed fstab
entries to be mounted before the system switches to the real-root, (as the
comments on top of this file claims) but there are still errors during boot.
Thanks
Francisco
