Questions and Answers

Bjorn Satdeva

I need to start by completing some unfinished business. In the November/December 1992 issue (vol.1, no.4) I explained how to use Archie. However, I did not mention which password to use. There is a good reason for this, as Archie does not require a password -- just log in on the server as Archie, and you are in business.

Sun User Group

In December, the Sun User Group held its trade show and conference in San Jose, California. I visited the show floor briefly, but did not see much in the way of interesting new hardware or software. The exception was a fast Terra Byte tape archive from Metrum Information Storage presented by Highland Digital. Unlike existing tape libraries, which use Exabyte or DAT tape drives, this server is based on drives that use large tape formats (they looked like VHS video tapes) and provide a much greater transfer rate than an Exabyte drive. At the time of the show, there was no software to make this tape library useful, but I was told that several vendors who have backup programs on the market were in the process of evaluating the tape library.

USL Bought by Novell

It has been reported that AT&T has sold its shares in UNIX System Laboratories (USL) to Novell, though the sale must still be approved by the stockholders of the two companies. It is far too early to speculate on what effect this development will have on UNIX System V Release 4 in the future, but one may hope that it will result in a much needed boost in software quality. One may further hope that the silly lawsuit against UC Berkeley and BSDI will be dropped.

And now to this month's questions.

Our organization is preparing to overhaul its news installation and there has been a lot of discussion about which news software we should be using. We wonder if you have any thoughts on the subject.

News software consists of two separate and distinct parts: the news delivery agent and the news reader.

There are a number of news delivery agents, the oldest being B-News, which is still used in many installations. B-News is probably the easiest to install in a vanilla configuration but, because of its complexity can be difficult to troubleshoot if it is used in an unusual configuration. A newer delivery agent is C-News, which, though in some ways still a bit rough around the edges, nevertheless delivers a significantly better performance than does B-News. If you are connected to the Internet, there is a new delivery system available; it's called INN, and it uses nntp (News Network Transfer Protocol). My choice has been to use C-News, and we have just completed installing the newest version, the C-News performance release (which to my knowledge has no version number).

There are a number of basic design issues you must consider when designing your news system. If your users will be reading news from more than one host, you will need to make it available on every host where a user might want to read news (or at least on a reasonable subset of such hosts, as, for example, all file servers). There are two ways to do this (apart from the traditional USENET transport, which is out of the question because of low performance): you can either NFS-mount the directory to all hosts supporting the news, or you can use nntp to connect to a single news server. C-News will support either method, while B-News would not, (at least not when I stopped using it a few years back).

If you are NFS-mounting the news directory, then your news reader will work almost as if it had been installed directly on the news server (with a bit of complication in posting the news). However, if your news reader supports nntp, you will not need the NFS mounts. Most modern news reader will support both NFS-mounting and nntp; however, if you have more than a few systems, I suggest that you go with the nntp scheme. Some of the available news reader which can use nntp are trn and nn (and on a larger site you will probably have to support both, as users want the news reader they are familiar with).

Another issue you will need to consider is the growing volume of news articles. If you want a full newsfeed, not only will you need a large capacity disk (500Mb or more), but within a a few years you will no longer be able to receive a day's news using a high speed within a 24-hour period. (This is amusing to me, considering that the first USENET connection I set up in the early 1980s was able to receive a full newsfeed, using a 1200-baud modem, in just two hours. A sign of progress maybe?

Further information about nntp can be found in rfc977.

The GNU people also offer some news software; however, I have never used it, and do not know much about it.

How many users can a system administrator support?

It depends on the skill level of the users, and the level of required support. Sites differ greatly, not only between but also within such categories as educational or commercial.

Users who need a lot of support will require additional manpower. Support at a high level for an extended period of time -- say 7:00 AM to 9:00 PM seven days a week -- would require several people. On the other hand, if users can solve most problems on their own, fewer people will be needed. At one extreme, I once supported a site consisting of 24 file servers and a little over 300 workstations singlehandedly for about three months. This was OK for a short period of time, but did not leave much time for user support.

Rob Kolstad (kolstad@bsdi,com) has been collecting data on the size of the user populations system administrators are supporting in various settings. This data has been posted to USENET, but if you send him e-mail, he will properly be willing to send you a copy. The material is very interesting, as it shows very large differences in the user-to-administration ratios found in real life.

In my judgement, a reasonable ratio in most cases would be something like five system administrators per one hundred users, dropping off for very large installations (if run properly, a large installation can be more efficient than a smaller one).

At our site we use the automounter to mount the users' home directories. As a result, the mechanism for naming the users' home directories is somewhat messy and unsystematic. How can we improve this?

In addition to the symbolic links already used by the automounter, you can add one more level of indirection, in the form of a symbolic link from /user/<username> to where the user's home directory exists on that machine (through the automounter mount-point or on the home machine, directly to where the directory is hard mounted). This will allow users and programs always to refer to a user's home directory as /user/<username>. Since this method is independent of where and how the user's home directory is mounted, not only gives users the advantage of a consistent naming scheme, but also gives the system administrator the advantages of being able to move users from one machine to another in a manner that is (almost) transparent. The drawback to this method is that, in order for it to work well, you will need to write a shell or Perl script that creates the links to a central table maintained by the system administrator. Otherwise, the links will, over time, become incorrect (and different from machine to machine), which in turn will cause serious login problems.

In a paper delivered at the LISA V conference, Arch Mott described in much more detail a similar method used at MIPS Computer Systems. Arch can be reached by e-mail at arch@cisco.com.

About the Author

Bjorn Satdeva -- email: bjorn@sysadmin.com /sys/admin, inc. The Unix System Management Experts (408) 241 3111 Send requests to the SysAdmin mailing list to sysadm-list-request@sysadmin.com