Subsystem Scripts

Each subsystem on a host has a controlling script which is very similar to the startup scripts used by the System V init mechanism. These scripts accept a number of methods such as start and stop which are invoked at appropriate times. Each script reads configuration parameters from the repository and configures the appropriate subsystem. This may involve translating the configuration parameters into a traditional configuration file, or controlling a service directly; for example, starting some daemon with command-line parameters derived from the configuration resources.

Traditionally, these scripts have been simple shell scripts although, under Linux, Perl is available at install time and many scripts now include some Perl code as well. A set of default routines are available which can be included into the script to load resources and perform other utility functions, such as retrieving default values for missing resources. Most scripts are quite short and it is easy to write a configuration script for a new package or service. Initially, new scripts are normally written just to support the subset of configuration parameters which are expected to vary in our installation, and this is easily expanded later as the need arises. The independence, and ease with which these scripts can be created has been a major reason for the success of the system; they are usually created by the person responsible for the corresponding service, and many people have contributed.

The example in section 8 shows a section of code from a script which starts the Samba server for VMware. Notice that most of the numerous Samba parameters are hardwired into a template configuration file, but those which we expect to vary between machines are set from the LCFG resources by a simple substitution of variables in the template. Some of these are also generated from a ``higher-level'' LCFG parameter which specifies whether or not we want the server to be visible on the external network. Notice also, that VMware itself is started using the standard init script.