1 Introduction

This manual documents the GNU Daemon Shepherd, or GNU Shepherd for short. The Shepherd looks after system services, typically daemons. It is used to start and stop them in a reliable fashion. For instance it will dynamically determine and start any other services that our desired service depends upon. As another example, the Shepherd might detect conflicts among services. In this situation it would simply prevent the conflicting services from running concurrently.

The Shepherd is the init system of the GNU operating system—it is the first user process that gets started, typically with PID 1, and runs as root. Normally the purpose of init systems is to manage all system-wide services, but the Shepherd can also be a useful tool assisting unprivileged users in the management of their own daemons.

Flexible software requires some time to master and the Shepherd is no different. But don’t worry: this manual should allow you to get started quickly. Its first chapter is designed as a practical introduction to the Shepherd and should be all you need for everyday use (see Jump Start). In chapter two we will describe the herd and shepherd programs, and their relationship, in more detail (herd and shepherd). Subsequent chapters provide a full reference manual and plenty of examples, covering all of Shepherd’s capabilities. Finally, the last chapter provides information for those souls brave enough to hack the Shepherd itself.

The Shepherd was formerly known as “dmd”, which stands for Daemon Managing Daemons (or Daemons-Managing Daemon?).

This program is written in Guile, an implementation of the Scheme programming language, using the GOOPS extension for object-orientation. Guile is also the Shepherd’s configuration language. See Introduction in GNU Guile Reference Manual, for an introduction to Guile. We have tried to make the Shepherd’s basic features as accessible as possible—you should be able to use these even if you do not know how to program in Scheme. A basic grasp of Guile and GOOPS is required only if you wish to make use of the Shepherd’s more advanced features.