Chapter 25 Linux, Solaris and contemporary UNIX

Objectives

To show the key developments in contemporary UNIX systems when compared with the basic Seventh Edition

Points to emphasise

• The overall structure of the system retains a monolithic kernel which exports services through a system-call interface. Additions such as Loadable Kernel Modules (Section 25.2) provide more flexibility over how the kernel is constructed, but the model of interaction remains the same.
• Adding support for multi-processor machines and multi-threaded processes has wide-ranging impacts on how the kernel is implemented and how concurrency is controlled. A modern UNIX kernel should be assessed both as a substrate over which concurrent programs are deployed and as a substantial example of one in itself.

• The successful ‘sockets’ interface (from BSD UNIX) highlights the issues that arise when trying to use a common API for file access, network access and IPC.

Possible difficulties

UNIX-derived systems are still under active development, most publicly in the case of the open-source Linux kernel. In assessing new features added to such systems it is important to remain critical of whether they present good long-term design decisions.

Teaching hints

• Many of the facilities covered in the chapter can form the basis of practical programming work. For example, students could compare the relative performance of the server designs sketched in Section 25.4 when interacting with clients over TCP network connections. Each design has its merits for particular workloads or in terms of ease of programming.
• The IPC APIs from System V and from BSD take very different approaches to tackling similar problems. Explore the advantages and disadvantages of each. A library-based project could examine the original discussions at the time of their design.