Erick Perez wrote:

I want to install centos 4.4 in a CF card and use a ram disk for operations. It means no hard disk attached to the computer. The machine will only run an antispam antivirus gateway. What documents can I read to make /var and /tmp sit on a ram disk and boot the operating system in read write and switch to read only after booting?

I have heard that there are read-write limitations that apply to some CF and similar implementations, and that the memory can "wear out" fairly quickly.

ipcop is designed to run from cf, I suggest you have a look at it. Whether you use it or not, it is likely to provide you with the education you need.

booting from a network can be a satisfactory alternative. You might need a boot floppy (or CD) to get enough intelligence to mount your root filesystem via NFS.

You could also contemplate booting & running from CD. Is there a CentOS-Live? If not, there is Fedora-Live, and you could also base from Knoppix (first, remove almost everything) or Damn Small Linux (Knoppix with almost everything removed, but some additions).

fwiw I recently installed Kubuntu 6.10 on a test system. It was fairly easy to create a separate root filesystem, and using PXE I can boot that on various systems and use it for emergency/repair/recovery/inspections in much the same way one would use Knoppix. Except I don't have to find the CD.

On Tue, 23 Jan 2007 11:48:42 -0500 "Erick Perez" eaperezh@gmail.com wrote:

What documents can I read to make /var and /tmp sit on a ram disk and boot the operating system in read write and switch to read only after booting?

One approach that you could take is mounting the filesystem read-only, and mounting a tmpfs filesystem as a writable overlay using unionfs. The following paper describes various approaches how you could do this:

http://www.am-utils.org/docs/sipek-ols2006/index.html

The CentOS live CD also uses unionfs (and squashfs), so it could be useful to look at that as a sample implementation.

-- Daniel

PS. unionfs is an additional kernel patch, and adding that to the CentOS kernel makes it an unsupported kernel. Though, precompiled kernels with unionfs are available through the Live CD build infrastructure on CentOS mirrors (/centos/4.4/build/livecd).