help understanding the livecd-creator tool - i need to make some customizations

[Bond Masuda]

hello,

i need to create a liveOS DVD with some unique requirements:

1) the root file system will be mounted directly off the DVD in read-only mode
2) i want to use in-memory disk for only /etc and /var for temporary non-persistent read-write

i have practiced using the livecd-creator tool to build a fedora-live-workstation and centos-7-livecd as a way to get familiar with the tool. it seems to me that the type of changes I want to make above, are not done in the kickstart %post section, so I assume it is done as part of the livecd-creator tool. I've read the README files, but I don't see a detailed description of how the root file system is configured to mount for the LiveOS. Looking over the steps described in the README, I *think* I need to better understand the following steps:
> Creates a live CD specific initramfs that matches the installed kernel
> Configures the boot loader

Is this the right direction to figure how to accomplish my above stated goals? If not, please help redirect me. If so, please help me understand those steps in more detail and how I can modify them to suite my needs.

thanks in advance...

[John Florian]

Not sure I follow exactly what you're trying to achieve.  Images produced by livecd-tools already provide an overlay backed by tmpfs so that /etc, /var and more functionally are writable.  However, those changes are not persistent -- if you reboot you're back to the original image.

If you truly want the root fs to be read-only, you might be able to use "mount -o remount,ro" somehow but lots more will likely be broken.  You may want to look into the dracut modules that do all the mounting work.  In particular, /usr/lib/dracut/modules.d/90dmsquash-live/dmsquash-live-root.sh may be informative.  Also worthy of note, dracut is really flexible at letting you wedge things in.  I've done this, but developing/testing is a chore considering you need to respin your image to test your new boot hooks.

--
John Florian
> -----Original Message-----
> From: B. Masuda [mailto:[e-mail]]
> Sent: Tuesday, June 14, 2016 14:10
> To: [e-mail]
> Subject: [Fedora-livecd-list] help understanding the livecd-creator tool -
> i need to make some customizations
>
> hello,
>
> i need to create a liveOS DVD with some unique requirements:
> the root file system will be mounted directly off the DVD in read-only
>
> mode
> 2) i want to use in-memory disk for only /etc and /var for temporary non-
> persistent read-write
>
> i have practiced using the livecd-creator tool to build a fedora-live-
> workstation and centos-7-livecd as a way to get familiar with the tool. it
> seems to me that the type of changes I want to make above, are not done in
> the kickstart %post section, so I assume it is done as part of the livecd-
> creator tool. I've read the README files, but I don't see a detailed
> description of how the root file system is configured to mount for the
> LiveOS. Looking over the steps described in the README, I *think* I need
> to better understand the following steps:
> > Creates a live CD specific initramfs that matches the installed kernel
> > Configures the boot loader
>
> Is this the right direction to figure how to accomplish my above stated
> goals? If not, please help redirect me. If so, please help me understand
> those steps in more detail and how I can modify them to suite my needs.
> thanks in advance...
>
> livecd mailing list
> [e-mail]
> https://lists.fedoraproject.org/admin/lists/[e-mail]

[Bond Masuda]

Thanks for the reply John.

On 06/14/2016 11:38 AM, John Florian wrote:
> Not sure I follow exactly what you're trying to achieve.  Images produced by livecd-tools already provide an overlay backed by tmpfs so that /etc, /var and more functionally are writable.  However, those changes are not persistent -- if you reboot you're back to the original image.

Can you tell me more where this tmpfs overlay happens? What step in the 
livecd-creator process does this get configured and where does it happen 
during the boot of the LiveOS?

I'm ok with the non-persistent changes; in fact, that's exactly what I'm 
looking for. What I'm looking for is that the rest of the filesystem 
(where possible without breaking function) is read-only. I assume this 
shouldn't be difficult since squashfs was designed for read-only. Is the 
overlay to allow writing done via unionfs or something like it?
> If you truly want the root fs to be read-only, you might be able to use "mount -o remount,ro" somehow but lots more will likely be broken.  You may want to look into the dracut modules that do all the mounting work.  In particular, /usr/lib/dracut/modules.d/90dmsquash-live/dmsquash-live-root.sh may be informative.  Also worthy of note, dracut is really flexible at letting you wedge things in.  I've done this, but developing/testing is a chore considering you need to respin your image to test your new boot hooks.

Where in the livecd-creator process does it call dracut? I assume this 
is what is used to create the initramfs?
> --
> John Florian
> > -----Original Message-----
> > From: B. Masuda [mailto:[e-mail]]
> > Sent: Tuesday, June 14, 2016 14:10
> > To: [e-mail]
> > Subject: [Fedora-livecd-list] help understanding the livecd-creator tool -
> > i need to make some customizations
> >
> > hello,
> >
> > i need to create a liveOS DVD with some unique requirements:
> > the root file system will be mounted directly off the DVD in read-only
> >
> > mode
> > 2) i want to use in-memory disk for only /etc and /var for temporary non-
> > persistent read-write
> >
> > i have practiced using the livecd-creator tool to build a fedora-live-
> > workstation and centos-7-livecd as a way to get familiar with the tool. it
> > seems to me that the type of changes I want to make above, are not done in
> > the kickstart %post section, so I assume it is done as part of the livecd-
> > creator tool. I've read the README files, but I don't see a detailed
> > description of how the root file system is configured to mount for the
> > LiveOS. Looking over the steps described in the README, I *think* I need
> > to better understand the following steps:
> > > Creates a live CD specific initramfs that matches the installed kernel
> > > Configures the boot loader
> >
> > Is this the right direction to figure how to accomplish my above stated
> > goals? If not, please help redirect me. If so, please help me understand
> > those steps in more detail and how I can modify them to suite my needs.
> > thanks in advance...
> >
> > livecd mailing list
> > [e-mail]
> > https://lists.fedoraproject.org/admin/lists/[e-mail]
>
> --
> livecd mailing list
> [e-mail]
> https://lists.fedoraproject.org/admin/lists/[e-mail]