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

[Francisco Ares <frares@gmail.com>]

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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@hotmail.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@gmail.com]
> *Sent:* 18 October 2013 18:16
> *To:* gentoo-embedded@lists.gentoo.org
> *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@hotmail.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@gmail.com]
> *Sent:* 16 October 2013 13:49
> *To:* gentoo-embedded@lists.gentoo.org
> *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****
>
> ** **
>

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