Can initramfs be mounted read-only?

Can initramfs be mounted read-only?

[David Wuertele]

I've been trying to create a system with a read-only rootfs using initramfs,
but I'm not having any luck.  I've included "ro" on my command line and when
I cat /proc/cmdline it reports "ro" like I expect.  But when I type "mount",
I see this:

  rootfs on / type rootfs (rw)

And I can create new files and write to them just fine.  Is it possible to
mount an initramfs read-only?

The documentation for early userspace and initramfs does not talk about
read/write permissions.

Thanks,
Dave

Re: Can initramfs be mounted read-only?

[Alan Jenkins]

On 8/12/09, David Wuertele <dave+gmane@wuertele.com> wrote:
> I've been trying to create a system with a read-only rootfs using initramfs,
> but I'm not having any luck.  I've included "ro" on my command line and when
> I cat /proc/cmdline it reports "ro" like I expect.  But when I type "mount",
> I see this:
>
>   rootfs on / type rootfs (rw)

Changing this could potentially break a lot of systems.  At least
Debian has "ro" as a default boot option, and it uses an initramfs by
default.

> And I can create new files and write to them just fine.  Is it possible to
> mount an initramfs read-only?
>
> The documentation for early userspace and initramfs does not talk about
> read/write permissions.

Have you tried running "mount / -oremount,ro" in an init script?

Regards
Alan

Re: Can initramfs be mounted read-only?

[David Wuertele]

Alan Jenkins <sourcejedi.lkml <at> googlemail.com> writes:

>> I've been trying to create a system with a read-only rootfs using initramfs,
> 
> Changing this could potentially break a lot of systems.  At least
> Debian has "ro" as a default boot option, and it uses an initramfs by
> default.

I don't want to change it for everybody, just my own system.  Since I'm not
using Debian, or any other distribution, I can handle the consequences.

>> Is it possible to
>> mount an initramfs read-only?
>
> Have you tried running "mount / -oremount,ro" in an init script?

Yes, and it works (the rootfs appears read-only after doing this).
I was hoping to get it to be read-only before init gets run.

Dave

Re: Can initramfs be mounted read-only?

[Christoph Lameter]

Try cramfs or romfs instead? Those are definitely readonly.