[Beowulf] Diskless Cluster Ram Disk Login

Julien Leduc julien.leduc at lri.fr
Mon Apr 23 16:05:16 EDT 2007


Hello Stephen,

it can be very frustrating to try to make a complete autonomous linux 
system  directly on an autonomous box.
So there are some clues:
1. try to build it in a controlled environment: virtual machine for 
example, or even a small chroot in your main environment to find out if 
you have all the devices, required libraries...
2. you can begin your work from a booting initrd + kernel: modify the 
initrd so that you stay in it, use tmpfs (or additional ramdisks), add 
network drivers, then you can format a bigger ramdisk (or use full tmpfs 
at the desired size mounted rw) and perform a pivot_root on it...

You should find plenty of documentation looking for "embedded linux 
HOWTO", it will be easier for you since you should avoid all the cross 
compilation tricky part.

For your ssh server you can try to use dropbear (smaller and specially 
designed for embedded systems), be sure you know what is done with dns: 
if your embedded system can resolve names? perform reverse on IPs? SSH 
can be picky when it comes to DNS questions.

For my usage, I have a hacked rsh server modified to avoid any DNS 
checks (every communication is based on IPs), and executes any command 
as root on the embedded system.
On big clusters RSH can cause some problems if you intend to keep more 
than 256 simultaneous connections from a single server.


Regards,

Julien Leduc



snj78 at comcast.net wrote:
> Hello everyone,
>  
> I have built a diskless cluster using FC6 x86_64 and can get a node to 
> successfully boot up via dhcp and pxelinux.  I am not using a NFS 
> because I want everything to reside on the node as to reduce network 
> traffic.  Right now it just boots up to a text login screen and it won't 
> accept any login or remote logins at all.  I have modified the rc 
> scripts in the root file system many times, even copying the whole /etc 
> directory straight over from the main PC, but it still won't allow any 
> logins.  I was able to to edit the inittab file to 'wait' at the shell 
> /bin/bash, but I still couldn't communicate with the node.  I am going 
> to try to install SSH, make sure the daemon sshd is running on the node 
> with pregenerated keys to allow logins without passwords, and see if 
> that will help any.  All I want to do is be able to boot the node up and 
> run an HPL benchmark on it.  What else do I have to do to the RAMDISK 
> root file system to communicate wit! h the h ead node and allow logins 
> via ssh, telnet, or even rsh so that I can get a benchmark?
> Thanks in advance for any help.
>  
> Stephen Jenkins
> WSU
> Beowulf Senior Project Group
> 
> 
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