Redhat 8.0 diskless cluster

[Ryan Sweet]

> 
> Fixed all the random pieces that assume a writable /.  Link /etc/mtab to
> /proc/mounts, /tmp -> /var/tmp, /root -> /var/root and similar.
> 
> mount /tftpboot/rh8/rw/<hostname> /var

A modification on this idea which goes a little further is to have a 
template /var (I call it var.pre-init), and to load that into a ram based 
filesystem.

I use a modified rc.sysinit to do the following:

Mount /tmp on procfs, 
copy var.preinit into /tmp (you can trim /var.preinit down to less than 
10 MB pretty easily, so this is quick)
mount --bind /var /tmp/var

Then the server stores no client specific data (unless you use 
dhcp-static, which is recommended if you want to know where your nodes are 
in the rack, for instance).

Of course you have to send your syslog and anything else you want to keep 
between reboots to another server.

Another benefit for us is that LAM/MPI (and anything else that uses /tmp)
gets a small speedup from working on a procfs filesystem.

It should also be noted that redhat's init scripts don't play well with 
nfsroot - in particular you have to make sure that restarting the network 
doesn't try to umount -a.

-- 
Ryan Sweet <ryan.sweet at atosorigin.com>
Atos Origin Engineering Services
http://www.aoes.nl