Managing a network of UNIX workstations

[Barr3y Jaspan]

Warning!  This is a long-ish article.

In article <3949 at jhunix.HCF.JHU.EDU>, barrett at jhunix.HCF.JHU.EDU (Dan
Barrett) writes:
> 
> 	I may be managing a network of DECstation 3100's running Ultrix in
> the near future.  I have been managing VAXen for a long time, but never a
> network of workstations.  So, I have some questions:

Reading your message, it sounds like you are trying to set up *EXACTLY*
what MIT's Project Athena has already set up.  I'll see if I can address
each of your points, explain Project Athena's solution.

> 
> (1)	How do you handle inter-machine superuser privileges?
> 
> 	I do NOT want to put "root" in /.rhosts -- this is a big security
> 	risk, right?

Athena uses the Kerberos Authentication System for authenication and
authorization (which, by the way, is a "bug free" authentication system
at least in its abstract form (ie: the implementation may have bugs)). 
Each host can have a file called ".klogin" that says which users can log
in to the host as root.  So, if I have already proved to Kerberos that I
really am "bjaspan at athena.mit.edu" and if the machine FOOBAR.MIT.EDU has
me in its .klogin file, then I can log in there as root.

> 
> (2)	How do you do transparent backups?  I want to pop a tape in ONE
> 	tape drive and say "Back up ALL files from ALL workstations onto
> 	this tape."
> 
> 	Suppose I dedicate one workstation as the "main node", mount all
> 	other workstation disks on the main node using NFS, and then back it
> 	up.  This should work...?  But don't I have to worry about
> 	inter-machine superuser privileges?  After all, we want to back up
> 	EVERY file from EVERY machine.
>
> (5)	Should we put disks on every workstation, or have one fileserver and
> 	many diskless workstations?  Which is better?  Easier to maintain?
> 
> 	My idea is to have one or two fileservers, make the other
> 	workstations use NFS, but put a small disk on each workstation for
> 	swapping only.  Good?  Bad?  What's better?
> 

These two are related, so I'll group them.  Athena has set up a number
of fileservers (which use Kerberos authentication to make sure they only
give files  to the right people) to store files.  Each "public
workstation" (of which there are approximately 1000 at the moment) has a
small hard disk which contains enough software for the machine to
function (many of the standard "system files" are also stored on
fileservers) and some local scratch space on a partition called "/site".
Filesystems from the fileservers are then mounted on the local disk
using NFS (and we are also currently experimenting with AFS, the Andrew
File System).

The backup problem then becomes easier.  You don't have to backup the
workstations at all, because no working files are stored there.  You
only have to backup the fileservers, and there is some limited number of them.

> 
> (3)	We'd like all users to have accounts on all workstations.  What's
> 	the best way to maintain an inter-machine password file?  I've
> 	heard vaguely of "yellow pages" but have never used it.
> 

Project Athena's solution to this problem is called "Hesiod", which it a
simple network database containing information for each user.  At
Athena, for example, Hesiod stores the following information (plus others):

    PASSWD: bjaspan:*:9123:101:Barr3y
Jaspan,,E40-342,34261,59604:/mit/bjaspan:/
bin/csh
    FILSYS: AFS /afs/athena.mit.edu/user/b/bjaspan w /mit/bjaspan
     POBOX: POP ATHENA-PO-2.MIT.EDU bjaspan

PASSWD is a standard password entry, except that password field itself
is the special character "*", meaning "ask the user for the password and
use Kerberos to do the authentication."  FILSYS says where my personal
filesystem is (which server, what path on that server, what the name of
the mountpoint on the local machine should be.  (My homedir is on AFS. 
An NFS entry looks like this:
"NFS /u1/lockers/testuser cyrus w /mit/testuser" -- it contains
essentially the same info.)  POBOX is used my the mailhub to determine
which machine stores my mail until I pick it up (mail server is
something you didn't mention.  A post office server holds my mail for me
until I call it up and ask for (using Kerberos to authenticate, of
course).  This way I can read my mail from any workstation.)

> (4)	We'd like a system where the entire network appears to each user as
> 	if it were one huge "machine".  A user would log onto this "machine"
> 	and not care which workstation s/he were actually using.  (Maybe the
> 	"machine" would automatically log the user onto the workstation with
> 	the lightest system load.  I've seen this done with VMS systems at
> 	other schools.)  Can this entire scheme be done?  Transparently?
> 

Well, at Athena, all workstations look essentially the same.  We have
VAXen, IBM RTs, and DECstation 3100s (running BSD4.3, BSD4.3, and
Ultrix, respectively) all running the X window system and the look
exactly the same to users.  (Well, almost.. :-)  Hesiod allows the
network services to be independent of which workstation a user is
actually logged on to.

One thing Athena doesn't do is the "using the machine with the lightest
load" trick.  The premise of Athena is that a workstation should be used
by a single user at a time (although of course they all support multiple
users) so any empty machine is the same as any other.


> 
> (6)	Does anybody make a removable media drive, like the Syquist
> 	44-megabyte cartridge drive, for the DS3100?
> 

I don't actually know what Project Athena uses to back up its
fileservers (I work for sysdev, not operations).  The Student
Information Processing Board (SIPB), however, has a tape drive made by
Exabyte that stores 2.2 GIGAbytes on an tape (we buy the tapes at our
local Tower Records store, and I think they're about $8 apiece.. most
people around here by Sony.)  We are currently running the Exabyte of a
VSII, but I think that is because we are using it to back up the SIPB
AFS cell, and the AFS software doesn't yet work on the DS3100 (we
actually have DS3100's in our office as well) but I seem to recall
hearing someone say that the drive does actually work with that machine.
 Incidentally, Exabyte has announced that they will be releasing a drive
that can store 5 gigabytes (instead of 2.2)
on the same tape by the end of this year.

I have no connection to Exabyte Corp.


> 	Thanks very much for your advice!
> 
>                                                         Dan

You're very welcome.  The best part about all this information that I've
given you is that the software to run it is FREE.  You can get Kerberos
and Hesiod by anonymous FTP from athena-dist.mit.edu.  There are also
things you didn't mention, like "How do users communicate with each
other?"  The answer is the Zephyr Notification Service, which you can
also get from athena-dist.  With all these services, you need a
service-management system, which we also have and is called Moira and
you can FTP it from.. you get the idea.  (Have you ever heard of a
networked conference system called "discuss"?  Well...)

This is a rough sketch of how we do things here.  There are more
knowledgeable people about running a network here that could be far more
useful to you.. 


Barry Jaspan, MIT-Project Athena
bjaspan at athena.mit.edu