Re: [uml-user] Network setup between UML <-> Host system

[D. J. A. <de...@ra...>]

On Mon, Jan 21, 2002 at 01:54:50PM +0200, ÁëÝîáíäñïò Êáñõðßäçò (Alexandros Karypidis) wrote:
> Hi everyone,
> 
> I understand that in order to have a network among UML and the host system, 
> UML must be launched by root.  

Not necessarily.

> Is there a way to provide networking by having 
> root launch the uml_net daemon and a simple user launching UML?

Yes.  One can have uml_net setuid root.  This is how the rpm I'm using works,
as downloaded from the sourceforge site:

$ rpm -q user_mode_linux
user_mode_linux-2.4.16.1um-0

$ rpm -ql user_mode_linux
/usr/bin/linux
/usr/bin/mkrootfs
/usr/bin/uml_mconsole
/usr/bin/uml_moo
/usr/bin/uml_net
/usr/bin/uml_switch
/usr/lib/uml/config
/usr/lib/uml/functions
/usr/lib/uml/modules-2.2.tar
/usr/lib/uml/modules-2.4.tar

$ ls -ld /usr/bin/uml_net
-rwsr-xr-x    1 root     root        18588 Dec  8 23:18 /usr/bin/uml_net*

The "s" indicates that when this binary runs, it will be run with the
permissions of the file owner, rather than with the permissions of the
account executing it.  In other words, uml_net will be run with root access,
even if called by an instance of the user-mode linux excutable launched by a
non-root user.

This is configured this way as well with the Debian packages.  I have used
this on both Debian and Redhat host systems to set up an external network
connection.  I use the network connection to add software to uml instances
running atop the small Debian root_fs image, via apt-get and external Debian
mirrors.

This has given me a lower-risk, lower-hassle way to gain experience with
networking tools, with Debian software installation, and with Debian
software mirrors.

--Joe

> I want to use UML in an Operating Systems Course and would like the host 
> system to export via NFS a directory to the UML boxes launched by the users.
> 
> Thanks
> 
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