The philosophy is much the same on large sites as on small ones and
has as its aim maximum reliability coupled with minimum support effort.
Wherever possible user home directories and applications software are concentrated
on one or a few central fileservers with adequate disk space and backup
facilities, and workstations are used solely as compute engines. This
means that to a first approximation workstations are installed in a standard
way (using predefined WorkInstructions)
and can easily be reinstalled if a system disk goes. A central mailhub
deals with all mail, hosting a central
spool area which is mounted on all workstations on top of their own /var/(spool)/mail.
All outgoing mail carries the address of the mailhub, not that of the workstation.
Printers and plotters are generally independently networked, and can be
hosted by both UNIX and PC servers; ideally on the UNIX side there
should be only one print/plot server, dedicated to the purpose. On a large
site the ORACLE database server is also usually separate.
All user IDs and all packages are available at all workstations ( unless there are particular requirements for this not to be so). To make this possible we rely heavily on NIS and the automounter . This also allows user home directories and applications software to be spread more widely than the ideal mentioned above, and indeed to share parts of the operating system itself.
In general users do not have the root passwords for their workstations, which helps to reduce the support to a minimum.
The NERC file structure is a framework for user home directories and applications packages, and includes a small collection of scripts designed to ease the installation and use of these on mixed-architecture sites. It also simplifies the installation of operating systems in a consistent manner, and helps greatly with the administration of licence managers and other package-related daemons.
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Support for CDE
In the same way as the NERC filestructure aims to make systems look alike to the user, a judicious choice of window manager can cover up differences between architectures. The Common Desktop Environment is now available on many of the current operating systems in NERC, and is becoming a standard. Releases of Solaris since 2.5 come with the Common Desktop as standard, as do HPUX 10.20 and DEC-Unix 4.0. Sun's OpenWindows is increasingly a minority system, particularly for public domain software, and we advise moving away from it where possible. Sun have not announced any intention to stop bundling OpenWindows with their operating system products.
Minimum of mods to vendor software
For UNIX, the / and /usr filesystems are likely to be completely replaced on an operating system upgrade so are best regarded as "belonging to the vendor". Occasionally links have to be inserted, or certain files replaced, but these are clearly defined in the installation scripts which we follow. Where these are related to an applications package they are grouped into a script called 'nercinstall' which lives in the package directory and can easily be re-executed after an upgrade.
However, we have moved away from installing proprietary software such as compilers in the /nerc/packages form and now let it install in the default locations as this is generally more satisfactory. The /nerc/packages form is retained as a shell, to contain only the setup and unsetup which control paths and environment variables.
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The NERC file structure is normally installed on one system per site, but may be set up stand-alone. This is a reversible process; scripts are included to invoke the site file system or the local one and to start and stop networking, as the workstation returns from its travels or goes away again.