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

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

[Francisco Ares]

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

[Grzegorz Borowiak]

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Every directory, which needs to be writable and persistent, needs to be
mounted as unionfs or AUFS, with one branch in read-only partition, and the
second one somewhere in /var. It's good to mount /etc that way and place
the factory defaults in the read-only branch of this. An alternative is to
allow only several files in /etc to be writable and move them to someplace
in /var (e.g. /var/etc) and leave symlinks in /etc (e.g. /etc/resolv.conf
-> /var/etc/resolv.conf).


On Wed, Oct 16, 2013 at 2:48 PM, Francisco Ares <frares@gmail.com> wrote:

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

[Gareth McClean]

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

[Francisco Ares]

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

[Gareth McClean]

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

[Francisco Ares]

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

[Francisco Ares]

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

[Rob Landley]

On 10/18/2013 12:15:35 PM, Francisco Ares wrote:
> 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.

You can have initramfs be tmpfs instead of ramfs now. New in the 3.12  
kernel. (Basically if CONFIG_TMPFS=y you get it for free unless you say  
rootfstype=ramfs or specify a root= to switch to, those enable the old  
legacy rootfs=ramfs behavior.)

If you're keeping initramfs around, it's generally a good thing. Means  
that df tells you how much space you have (and things like rpm that  
care actually get a nonzero size), and if you cat /dev/zero > /blah.txt  
as root the filesystem fills up and _stops_ rather than panicing the  
kernel.

Rob