[Buildroot] Newbie boot and fs mount question

[Buildroot] Newbie boot and fs mount question

[Mathew Benson]

How do I mount / from sda1 rather than RAM disk?

Sorry for the simple question and let me know if there is a better forum
for this.  I'm new to buildroot and busybox and haven't compiled a custom
kernel in at least 15 years.  I'm using the latest version of buildroot as
of this weekend, used the predefined i386 config, and built with kernel
version 3.8.17.  It seems to boot just fine but it appears the file system
is mounted from the initial RAM disk.  Any change I make to the file system
is volatile.  What do I need to do to make it mount / from sda1 instead of
the RAM disk?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.busybox.net/pipermail/buildroot/attachments/20151222/2cc00e13/attachment.html>

[Buildroot] Newbie boot and fs mount question

[Thomas Petazzoni]

Dear Mathew Benson,

On Tue, 22 Dec 2015 10:07:35 -0600, Mathew Benson wrote:
> How do I mount / from sda1 rather than RAM disk?

Pass root=/dev/sda1 on your kernel command line.

> Sorry for the simple question and let me know if there is a better forum
> for this.  I'm new to buildroot and busybox and haven't compiled a custom
> kernel in at least 15 years.  I'm using the latest version of buildroot as
> of this weekend, used the predefined i386 config, and built with kernel
> version 3.8.17.  It seems to boot just fine but it appears the file system
> is mounted from the initial RAM disk.  Any change I make to the file system
> is volatile.  What do I need to do to make it mount / from sda1 instead of
> the RAM disk?

We don't have anything like a "predefined i386 config".

However, you can see how to use a root filesystem from storage by
looking/building our Qemu x86-64 configuration:

	make qemu_x86_64_defconfig
	make

And then read board/qemu/x86_64/readme.txt for the details on how to
start this configuration under Qemu. You can see in this readme file
that we're booting the kernel with root=/dev/sda, since the first hard
drive is emulated using the contents of output/images/rootfs.ext2.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

[Buildroot] Newbie boot and fs mount question

[Mathew Benson]

I have root=/dev/sda1 on my kernel command line.

Yes, I ran make qemu_x86_64_defconfig followed by make.  I'm eventually going to load this build on a small PC, but for now, temporarily, I'm using virtual box.  I added a shared drive to both my development VM and my simulated PC VM.  I setup the first partition as bootable with grub.  I also enabled the creation of a rootfs.tar file.  After I run make, I mount the shared drive, and untar the rootfs.tar over the mounted drive, and copy the bzImage over.  The file system is still read only.

I have a possible dumb question.  I enabled initrd to be linked into the kernel, thinking boot time might be faster.  I enabled the "remount filesystem" option, thinking that would remount it from the hard drive rather than the linked in rootfs.  Is that an incorrect assumption?

Sent from my iPad

> On Dec 22, 2015, at 2:09 PM, Thomas Petazzoni <thomas.petazzoni@free-electrons.com> wrote:
> 
> Dear Mathew Benson,
> 
>> On Tue, 22 Dec 2015 10:07:35 -0600, Mathew Benson wrote:
>> How do I mount / from sda1 rather than RAM disk?
> 
> Pass root=/dev/sda1 on your kernel command line.
> 
>> Sorry for the simple question and let me know if there is a better forum
>> for this.  I'm new to buildroot and busybox and haven't compiled a custom
>> kernel in at least 15 years.  I'm using the latest version of buildroot as
>> of this weekend, used the predefined i386 config, and built with kernel
>> version 3.8.17.  It seems to boot just fine but it appears the file system
>> is mounted from the initial RAM disk.  Any change I make to the file system
>> is volatile.  What do I need to do to make it mount / from sda1 instead of
>> the RAM disk?
> 
> We don't have anything like a "predefined i386 config".
> 
> However, you can see how to use a root filesystem from storage by
> looking/building our Qemu x86-64 configuration:
> 
>    make qemu_x86_64_defconfig
>    make
> 
> And then read board/qemu/x86_64/readme.txt for the details on how to
> start this configuration under Qemu. You can see in this readme file
> that we're booting the kernel with root=/dev/sda, since the first hard
> drive is emulated using the contents of output/images/rootfs.ext2.
> 
> Best regards,
> 
> Thomas
> -- 
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com

[Buildroot] Newbie boot and fs mount question

[Thomas Petazzoni]

Dear Mathew Benson,

On Wed, 23 Dec 2015 19:04:05 -0600, Mathew Benson wrote:

> I have a possible dumb question.  I enabled initrd to be linked into
> the kernel, thinking boot time might be faster.  I enabled the
> "remount filesystem" option, thinking that would remount it from the
> hard drive rather than the linked in rootfs.  Is that an incorrect
> assumption?

Yes, it is an incorrect assumption. In Buildroot, if you enable
"initial RAM filesystem linked into linux kernel", then the entire
root filesystem lives in RAM, and we never switch to another on-storage
filesystem.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

[Buildroot] Newbie boot and fs mount question

[mathew.benson]

Got it working. ?Thanks.


Sent via the Samsung Galaxy S? 6, an AT&T 4G LTE smartphone-------- Original message --------From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Date: 12/24/2015  1:30 AM  (GMT-06:00) To: Mathew Benson <mathew.benson@gmail.com> Cc: buildroot at busybox.net Subject: Re: [Buildroot] Newbie boot and fs mount question 
Dear Mathew Benson,

On Wed, 23 Dec 2015 19:04:05 -0600, Mathew Benson wrote:

> I have a possible dumb question.? I enabled initrd to be linked into
> the kernel, thinking boot time might be faster.? I enabled the
> "remount filesystem" option, thinking that would remount it from the
> hard drive rather than the linked in rootfs.? Is that an incorrect
> assumption?

Yes, it is an incorrect assumption. In Buildroot, if you enable
"initial RAM filesystem linked into linux kernel", then the entire
root filesystem lives in RAM, and we never switch to another on-storage
filesystem.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.busybox.net/pipermail/buildroot/attachments/20151224/62d7089c/attachment.html>