Service directories

A service directory is a directory containing all the information related to a service, i.e. a long-running process maintained and supervised by s6-supervise.

(Strictly speaking, a service is not always equivalent to a long-running process. Things like Ethernet interfaces fit the definition of services one may want to supervise; however, s6 does not provide service supervision; it provides process supervision, and it is impractical to use the s6 architecture as is to supervise services that are not equivalent to one long-running process. However, we still use the terms service and service directory for historical and compatibility reasons.)


A service directory foo may contain the following elements:


With the evolution of s6, it is possible that s6-supervise configuration uses more and more files in the service directory. The notification-fd and timeout-finish files, for instance, have appeared in 2015; users who previously had files with the same name had to change them. There is no guarantee that s6-supervise will not use additional names in the service directory in the same fashion in the future.

There is, however, a guarantee that s6-supervise will never touch subdirectories named data or env. So if you need to store user information in the service directory with the guarantee that it will never be mistaken for a configuration file, no matter the version of s6, you should store that information in the data or env subdirectories of the service directory.

Where to store my service directories ?

Service directories describe the way services are launched. Once they are designed, they have little reason to change on a given machine. They can theoretically reside on a read-only filesystem - for instance, the root filesystem, to avoid problems with mounting failures.

However, two subdirectories - namely supervise and event - of every service directory need to be writable. So it has to be a bit more complex. Here are a few possibilities.