I notice the requirements for 280 MB of RAM for PXE booting in the Handbook:

http://www.sysresccd.org/Sysresccd-manu ... rk_booting

Is there anyway to PXE boot with only 256 MB of (or even less) RAM? My initial thoughts were of NFS (mounting the root filesystem through NFS, not downloading the sysrcd.dat), but I'm getting the impression that NFS booting is deprecated, undocumented and unreliable when tried.

The last few systems I've had to work on all had 256 MB, which at first I found to be an odd coincidence, but then, that's about typical for the age of the machines with dying hard drives. (yes all the machines had NIC's with PXE - business PCs)

Any thoughts on how I could successfully boot System RescueCD via PXE on a system with (or less than) 256MB RAM?

Yes there is a way: you must shrink the size of sysrcd.dat. It means you will have to make a customized SystemRescueCd and you will have to erase the files you don't use before you recreate the new squashfs filesystem (sysrcd.dat).

For instance you should remove the kernel modules you don't use (located in /lib/modules/), he documentation, the locales, ...

I've successfully shrinked sysresccd.dat down from 148MB (1.0.0-rc2) to 75MB by aggressively removing lots of things, but when tried to boot with the new one on a 256MB RAM equipped box it still failed to load this new one with no more ram available :cry:
If anybody has an idea what could I still change please tell me.

We need more details about the problem...

I've built up a smaller sysrcd.dat using the customization method (/mnt/custom/customcd/files) described in the docs, removed X, firefox, docs, a few other things, built up a new sysrcd.dat (75MB in size, while the original 1.0.0-rc2 was 148MB and failed to download at about 60% completed), but my 256MB RAM equipped test machine still failed to download it via http giving up due to no more available memory at about 70%.
In the past I've set up everything (dhcp, tftp, http) and can successfully use it with machines with more RAM.

I think it's still too big. You can remove the kernel related files for the kernel that you don't use (clean /lib/modules), and compress with a better level (use 262144 for the blocksize in the mksquashfs-lzma command: you have to edit sysresccd-custom to change that option.

Following the described method I was able to build a 67M sysrcd.dat which downloads entirely, but there is not enough memory get unpacked.
I think I could remove more unneeded stuff (actually besides som basic stuff I would only need partimage, sfdisk, network (dhcp) smbfs or cifs or ftpfs) but I was quite conservative in removing things, trying not to remove some needed dependency.
Next I've copied the svn repository and going to do things in the opposite order: instead of blindly remove things from the system, to select only the tools and build up a custom (very small system).
What I would ask for is some pointers to the description of the build process.

Thank you