dinit

Dinit

v0.17.0pre (alpha release #9)

This is the README for Dinit, the service manager and init system. It is intended to provide an overview; For full documentation please check the manual pages. The impatient may wish to check out the getting started guide.

Dinit is used as the init system for Chimera Linux, and is an init system option for Artix Linux.

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Dinit is free software. You may wish to consider sponsoring Dinit's development.

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Contents

1. Introduction
   1. Features
   2. Target platforms
   3. Other information
2. Reporting issues
3. Configuring services
   1. Service types
   2. Service description files
4. Running Dinit
5. Controlling services
   1. Service hierarchy and states
   2. Using dinitctl

Introduction

Dinit is a service supervisor with dependency support which can also act as the system "init" program. It was created with the intention of providing a portable init system with dependency management, that was functionally superior to many extant inits. Development goals include clean design, robustness, portability, usability, and avoiding feature bloat (whilst still handling common - and some less-common - use cases). Dinit is designed to integrate with rather than subsume or replace other system software.

Features

Dinit can launch multiple services in parallel, with dependency management (i.e. if one service's operation depends on another, the latter service will be started first). It can monitor the process corresponding to a service, and re-start it if it dies, and it can do this in an intelligent way - first "rolling back" all dependent services, and restarting them when their dependencies are satisfied. The dinitctl tool can be used to start or stop services and check their state.

Dinit is designed to run as either as a system service manager (runs as root, uses system paths for configuration) or a user process (runs as a user, uses paths in the user's home directory for configuration).

Target platforms

Dinit is designed to work on POSIXy operating systems such as Linux and OpenBSD. It is written in C++ and uses the Dasynq event handling library, which was written especially to support Dinit. (Note that a copy of Dasynq is bundled with Dinit, so a separate copy is not required for compilation; however, the bundled copy does not include the documentation or test suite).

Other information

See doc/COMPARISON for a comparison of Dinit with similar software packages.

Dinit is licensed under the Apache License, version 2.0. A copy of this license can be found in the LICENSE file.

This software was written by Davin McCall davmac@davmac.org with contributions from many others. See CONTRIBUTORS.

See BUILD for information on how to build Dinit. See the doc directory for information on design, code style, guidelines for contributions, and end-user-oriented documentation.

Reporting issues

Please use Github issues to report bugs, and provide as much information as is necessary to reliably reproduce the issue.

Please do not file feature requests unless you are working on system integration (eg. you are a package maintainer for a distribution that supports Dinit, or you are working to provide Dinit support for a particular distribution) and need to solve a real problem, or unless you are willing to provide patches (in this case you can open an issue for discussion - in which case please also see the CONTRIBUTING file).

Configuring services

This section and the following sections are intended as an introductory guide, and to give a feel for what using Dinit is like. For a complete reference, see the man pages: dinit(8) and dinit-service(5).

Service types

A "service" is nominally a persistent process or system state. The two main types of service are a process service (represented by a an actual process) and a scripted service (which is started and stopped by running a process - often a shell script - to completion). There are also bgprocess services and internal services. See the dinit-service(5) manual page for details.

Many programs that you might want to run under Dinit's supervision can run either "in the foreground" or as a daemon ("in the background"), and the choice is dictated by a command line switch (for instance the -D and -F switches to Samba's "smbd"). Although it might seem counterintuitive, the "foreground" mode should be used for programs registered as process services in Dinit; this allows Dinit to monitor the process.

Service description files

Dinit discovers services by reading service description files. These files reside in a directory (/etc/dinit.d is the default "system" location, with /usr/local/lib/dinit.d and /lib/dinit.d also searched; the default user location is $HOME/.config/dinit.d) and the name of a service description file matches the name of the service it configures.

For example, a service named "mysql" might be configured via the service description file named /etc/dinit.d/mysql. Service descriptions are loaded lazily, as needed by Dinit; so, this service description file will usually be read when the mysql service is first started.

(An example of a complete set of system service descriptions can be found in the doc/linux/services directory).

A service description file has a textual format and consists of a number of parameter settings. Some examples of the available parameters are:

type = process | bgprocess | scripted | internal
command = ...
stop-command = ...
run-as = (user-id)
restart = (boolean)
logfile = ...
pid-file = ...
options = ...
depends-on = (service name)
depends-ms = (service name)
waits-for = (service name)

Typically, a service which runs as a process will use the command setting, and include a waits-for dependency on a number of other services (to ensure that the system is ready for general operation). For example, a service description for sshd might look like the following:

type = process
command = /usr/sbin/sshd -D
waits-for = syslogd
depends-on = loginready

In this example, syslogd and loginready are also services (which must have their own service descriptions).

A wide range of service settings and options are available. Please see the manual page for a full list.

Running Dinit

The main Dinit executable is called dinit.

Dinit can run as the system "init" - the first process started by the kernel on boot - which is normally done by linking or copying dinit to /sbin/init. This is currently supported only on Linux. It requires having suitable service descriptions in place and should be attempted only by those comfortable with low-level system administration and recovery. See doc/linux directory for more information.

Dinit can also run as a normal process, and can be started in this case by a regular user.

By default, regardless of whether it runs as a system or user process, Dinit will look for and start the service named "boot". This service should be configured with dependencies which will cause any other desired services to start. You can specify alternative services to start via the dinit command line (consult the manual page for more information).

Controlling services

Service hierarchy and states

Services can depend on other services for operation, and so form a dependency hierarchy. Starting a service which depends on another causes that other service to start (and the first service waits until the latter has started before its process is launched and it is itself considered started).

Services are considered active when they are not stopped. Services can also be explicitly marked as active (this normally happens when you explicitly start a service). Finally, a service with an active dependent is also considered active.

If a service stops and becomes inactive (i.e. it is not explicitly marked active and has no active dependents) then any services it depends on will also be stopped (becoming inactive) unless they have other active dependents, or they were explicitly started and marked active.

What this means is that, in general, starting an (inactive, stopped) service and then stopping it will return the system to its prior state - no dependencies which were started automatically will be left running.

Using dinitctl

You can use the "dinitctl" utility to start and stop services. Typical invocations are:

dinitctl start <service-name>
dinitctl stop <service-name>
dinitctl release <service-name>
dinitctl status <service-name>
dinitctl list

Note that a start marks the service active, as well as starting it if it is not already started; the opposite of this is actually release, which clears the active mark and stops it if it has no active dependent services.

The stop command by default acts as a release that also causes the service to stop. If stopping a service would also require a dependent service to stop, a warning will be issued; the --force option will be required to bypass the warning, though it is generally advisable to stop the dependent systems manually one-by-one - indirectly force-stopping the boot service may cause every service to stop, ending user sessions!

When run as root, dinitctl (by default) communicates with the system instance of dinit. Otherwise, it communicates with a user (personal) instance. This can be overridden (using -u or -s for the user or system instance, respectively), but note that regular users will generally lack the required permission to communicate with the system instance, which is intended to be controlled only by the root user.

Here is an example command for starting a service:

dinitctl start mysql   # start mysql service

You can "pin" a service in either the stopped or started state, which prevents it from changing state either due to a dependency/dependent or a direct command:

dinitctl start --pin mysql  # start mysql service, pin it as "started"
dinitctl stop mysql  # removes activation, service doesn't stop due to pin
dinitctl unpin mysql # release pin; service will now stop

You can pin a service in the stopped state in order to make sure it doesn't get started accidentally (either via a dependency or directly) when you are performing administration or maintenance.

Check the state of an individual service using the "status" subcommand:

dinitctl status mysql

The output will tell you the current service state; for a running service, it may look something like the following:

Service: mysql
    State: STARTED
    Activation: explicitly started
    Process ID: 3393

Finally, you can list the state of all loaded services:

dinitctl list

This may result in something like the following:

[[+]     ] boot
[{+}     ] tty1 (pid: 300)
[{+}     ] tty2 (pid: 301)
[{+}     ] tty3 (pid: 302)
[{+}     ] tty4 (pid: 303)
[{+}     ] loginready (has console)
[{+}     ] rcboot
[{+}     ] filesystems
[{+}     ] udevd (pid: 4)
[     {-}] mysql

The above represents a number of started services and one stopped service (mysql). Only the boot service is marked active ([+] rather than {+}); all other services are running only because they are (directly or indirectly) dependencies of boot. Services transitioning state (starting or stopping) are displayed with an arrow indicating the transition direction:

[[ ]<<   ] mysql     # starting (and marked active)
[   >>{ }] mysql     # stopping

The brackets indicate the target state, which may not be the state to which the service is currently transitioning. For example:

[   <<{ }] mysql     # starting, but will stop after starting
[{ }>>   ] mysql     # stopping, but will restart once stopped

Remember that a starting service may be waiting for its dependencies to start, and a stopping service may be waiting for its dependencies to stop.

For a complete summary of dinitctl command line options, use:

dinitctl --help

Or, for more detailed help, check the manual page for dinitctl.