CentOS - May 2008 - read only root file system

I am looking at having a read only box, it will not use a swap partition.
Any recommendations?

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> I am looking at having a read only box, it will not use a swap partition.
> Any recommendations?
Why bother with a hard drive at all?  Customize a Live CD/DVD and remove 
the hard drive alltogether.

Barry

On Fri, May 2, 2008 at 12:16 AM, Jason Pyeron <jpyeron at pdinc.us>
wrote:
> I am looking at having a read only box, it will not use a swap partition.
>  Any recommendations?
You'll need to break out your hard drive into multiple partitions, as
there are certain portions of the file system that need to be writable
such as /var and /home.  I setup systems in this manner to make them
more difficult to subvert, I'd suggestion searching for topics such as
"linux file system hardening".

When you do need to do maintenance, such as package management, you'll
need to remount the root file system as writable which will likely
require a reboot.

Brett

On Fri, May 2, 2008 at 12:16 AM, Jason Pyeron <jpyeron at pdinc.us>
wrote:
> I am looking at having a read only box, it will not use a swap partition.
>  Any recommendations?
Here is a slide deck from a presentation Rick Troth has done on read
only root file systems.

http://linuxvm.org/present/SHARE110/S9216rt.pdf

Might be some helpful bits of information in there for you.

Good luck!
Jeffrey

Responding to a question posted earlier this month, Centos 5.1 includes
configuration files for enabling the read-only root filesystem.
Actually, all filesystems can be mounted read-only with particular files
and directories mounted on a read-write tmpfs (in RAM). This capability
comes directly from the upstream provider.

You can have your Centos system running read-only root in two
easy steps:
1.  Edit /etc/sysconfig/readonly-root and change READONLY=no to
    READONLY=yes
2.  Reboot

When your computer comes back up, the root and any other system
partitions will be mounted read-only.  All the files and directories
listed in /etc/rwtab will be mounted read-write on a tmpfs filesystem.
You can add additional files and directories to rwtab to make them
writable after reboot.

Note that this system is stateless.  When you reboot again, everything
written to the tmpfs filesystem vanishes and the system will be exactly
as it was the last time it was booted. You could add a writable
filesystem on disk or NFS for writing files you want to retain after
rebooting.

Take a look at /etc/rc.d/rc.sysinit to see how the magic is done.

This capability is a "technology preview" (beta) and is buggy. Note
that
/etc/mtab and thus "mount" do not show the complete list of
filesystems
because the /etc directory is on a read-only filesystem.  /proc/mounts
always shows the correct mount information.  You could update /etc/mtab
from /proc/mounts to correct it both after boot and after running the
mount or umount commands to change mounts.

Run "fgrep -v rootfs /proc/mounts >/etc/mtab" to correct /etc/mtab.
Note that mounting or symlinking /proc/mounts to /etc/mtab causes other
problems such as breaking the df command.

You can change your read-only root filesystem to read-write mode
immediately with this command run by the root user:
mount -n -o remount,rw /

      - Fred

On Saturday 24 May 2008 12:05:30 Fred Noz wrote:
> Responding to a question posted earlier this month, Centos 5.1
> includes configuration files for enabling the read-only root
> filesystem. Actually, all filesystems can be mounted read-only with
> particular files and directories mounted on a read-write tmpfs (in
> RAM). This capability comes directly from the upstream provider.
> When your computer comes back up, the root and any other system
> partitions will be mounted read-only.  All the files and directories
> listed in /etc/rwtab will be mounted read-write on a tmpfs filesystem.
> You can add additional files and directories to rwtab to make them
> writable after reboot.
>
> Note that this system is stateless.  When you reboot again, everything
> written to the tmpfs filesystem vanishes and the system will be
> exactly as it was the last time it was booted. You could add a
> writable filesystem on disk or NFS for writing files you want to
> retain after rebooting.
This is very interesting. Thanks for the sharing Fred. So, it's somekind
of Live CD on a disk? I can't think of a practical benefit of using such
system, is it to protect it from unwanted modification?

Fajar Priyanto | Reg'd Linux User #327841 | Linux tutorial
-----

Fajar, 
There are many practical reasons why one would want to run a
Linux system, whether it be desktop or server, with a read-only root.

One reason is for ease of maintenance, especially when there are many
systems to maintain.  You might be administering computers in a
classroom, internet access point, or library and you want to be
certain that after reboot, the system is exactly as it was the last
time it was rebooted, even if the users mess with the system
accidentally or on purpose.

For example, if a user fills up the /tmp filesystem and causes the
system to crash, after booting, the system will have an empty /tmp
filesystem.  It will not require that fsck to be run because the other
filesystems were mounted read-only.  This implies no risk of filesystem
corruption (except due to physical failures on the disk).  Not needing
fsck saves time on boot.

You could use read-only root on embedded systems where there is no way
an administrator could get to the system to fix it.

Read-only root is beneficial on a system running on flash media because
this avoids having recurring writes wear out some sectors on the media.

This is a practical way to run a large group of diskless systems.  A
single read-only root filesystem can be made available on a network from
an NFS server.  Many diskless clients can use this readonly-root
simultaneously.

Of course, this is a way to implement a live CD.

In addition to easy maintenance, readonly-root adds a layer of security. 
The security is broken if someone gains access to the root user, but 
then many security protections are lost if someone gains root.

Even a Database server can benefit from being run on read-only root.
The data disk would certainly be mounted read-write, but there is
no reason why the operating system and database application software
need to be on disks mounted read-write.

When an administrator wants to perform an update, upgrade, software,
installation. or other system change, the administrator sets the
readonly filesystems to read-write using a simple mount command.
After the administrator finishes making the changes, a simple mount
command (or reboot) sets the readonly filesystems back to read-only.

Of course, on systems where the root and system filesystems have 
no physical write capability, such as on a live CD, they cannot be
set to read-write.

     - Fred
---------
  Fred Noz
  Fred at Noz.net