Re: [gentoo-embedded] planning a flash DOM x86 embedded system

[Francisco Ares]

Found it and gonna try:

https://grangerx.wordpress.com/2010/12/31/using-fuse-unionfs-with-centos-5-5-i686/


2013/10/22 Francisco Ares <frares@×××××.com>

> Thanks for the tip, Gareth;
>
> As a matter of fact, the unionfs in "/var" is not being mounted - as long
> as "/etc" also.
>
> Finally I got a verbose boot, and it is possible to read, as an error
> message:
>
> !! unable to mount none for /var
>
> in my "/etc/fstab", these are the related entries:
>
>
>
> /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
>
> Now I'm trying to find out on the manuals how to better tell the mount
> program there is no device to be mounted for "/var" .
>
> Thanks
> Francisco
>
>
>
> 2013/10/20 Gareth McClean <disneysw@×××××××.com>
>
>> ** **
>>
>> 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:frares@×××××.com]
>> *Sent:* 18 October 2013 18:16
>> *To:* gentoo-embedded@l.g.o
>> *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 <disneysw@×××××××.com>****
>>
>>  ****
>>
>> 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:frares@×××××.com]
>> *Sent:* 16 October 2013 13:49
>> *To:* gentoo-embedded@l.g.o
>> *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****
>>
>> ** **
>>
>
>