Option Directories -- Master

This shows the layout of the opt directory on our master node. Note that it isn't that machine's /opt directory, although it could be. On another network, we have exactly that arrangement--the /opt directory is the master opt directory for the whole network. On the machine shown here (which is the "srvr01" from the overview), the actual /opt directory is set up to point to this directory, just as it is on workstations. The only difference is that its /opt/mstr link has the simpler value "/_c/opt.10".

The salient points of this structure are

• the presence of the pkg and site subdirectories, and
• the fact that the /opt/appname directories aren't directories at all, but are symbolic links.

The pkg subdirectory serves to contain the actual application directories for net-supported packages. If you can retrieve it from a public archive site, it goes into pkg.

The site directory contains things that we build and maintain ourselves. In our particular case, this means locally developed tools, not actual product code. As noted in the Open Questions section, locally-developed code (even tools) at our site is kept under configuration control (ClearCase), so we copy released files into the appropriate /opt/site/appname-n.nn directory as part of the release process.

The /opt/appname links serve several purposes:

• You can do an "ls -l /_c/opt.10" on the master node and see at a glance which packages are installed, whether they are net- or locally-supported, and what versions of them are being presented to the workstations.
• They enable you to switch versions in an instant. This need arises
  • when upgraded versions of packages turn out to have problems and you need to roll back to an old version to keep production going,
  • to roll back to an old version to test something,
  • to switch to a new version briefly to "dip your toe in the water", or
  • when just plain upgrading to a newer version.
• They are otherwise generic. The name under which the rest of the world sees a package does not contain a version number. Any configuration file, link, or other pointer should always use the name /opt/appname, and trust that the system administrators are providing the "right" version. This rule can be broken only under the most unusual of circumstances.