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[Shepherd][PATCH 3/4] doc: Move manual to the 'doc' directory.
|
From: |
Mathieu Lirzin |
|
Subject: |
[Shepherd][PATCH 3/4] doc: Move manual to the 'doc' directory. |
|
Date: |
Wed, 27 Jan 2016 21:45:33 +0100 |
* doc/shepherd.texi: Moved from the root directory.
* doc/fdl-1.3.texi: Likewise.
* Makefile.am (info_TEXINFOS): Add a 'doc/' prefix to 'shepherd.texi'.
(EXTRA_DIST): Remove 'fdl-1.3.texi'.
(doc_shepherd_TEXINFOS): New variable.
* .gitignore: Update it.
---
.gitignore | 49 +-
Makefile.am | 4 +-
doc/fdl-1.3.texi | 505 +++++++++++++++++
doc/shepherd.texi | 1593 +++++++++++++++++++++++++++++++++++++++++++++++++++++
fdl-1.3.texi | 505 -----------------
shepherd.texi | 1593 -----------------------------------------------------
6 files changed, 2125 insertions(+), 2124 deletions(-)
create mode 100644 doc/fdl-1.3.texi
create mode 100644 doc/shepherd.texi
delete mode 100644 fdl-1.3.texi
delete mode 100644 shepherd.texi
diff --git a/.gitignore b/.gitignore
index 7cb94f2..111817f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,26 +1,29 @@
-/configure
-/shepherd.info
-/stamp-vti
-/version.texi
+*.go
+*~
+,*
+.dirstamp
+/*.1
+/*.8
+/INSTALL
+/aclocal.m4
+/autom4te.cache
+/build-aux/*
/config.cache
/config.log
/config.scm
/config.status
-/herd
-/shepherd
+/configure
+/doc/shepherd.info
+/doc/stamp-vti
+/doc/version.texi
/examples/Makefile
-/autom4te.cache
-/build-aux/*
-Makefile.in
-Makefile
-*~
-,*
+/halt
+/herd
/missing
-/texinfo.tex
-/INSTALL
-/aclocal.m4
-*.go
/modules/shepherd/config.scm
+/modules/shepherd/system.scm
+/reboot
+/shepherd
/shepherd.aux
/shepherd.cp
/shepherd.cps
@@ -28,28 +31,26 @@ Makefile
/shepherd.fns
/shepherd.ky
/shepherd.log
+/shepherd.pdf
/shepherd.pg
/shepherd.toc
/shepherd.tp
/shepherd.tps
/shepherd.vr
/shepherd.vrs
-/modules/shepherd/system.scm
-/halt
-/reboot
-/shepherd.pdf
/test-suite.log
/tests/basic.log
/tests/basic.trs
/tests/misbehaved-client.log
/tests/misbehaved-client.trs
-/tests/respawn.log
-/tests/respawn.trs
/tests/no-home.log
/tests/no-home.trs
+/tests/respawn.log
+/tests/respawn.trs
/tests/sigint.log
/tests/sigint.trs
/tests/status-sexp.log
/tests/status-sexp.trs
-/*.1
-/*.8
+/texinfo.tex
+Makefile
+Makefile.in
diff --git a/Makefile.am b/Makefile.am
index 2985a86..52f66d6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -66,7 +66,8 @@ CLEANFILES = \
$(bin_SCRIPTS) $(sbin_SCRIPTS)
# Documentation.
-info_TEXINFOS = shepherd.texi
+info_TEXINFOS = doc/shepherd.texi
+doc_shepherd_TEXINFOS = doc/fdl-1.3.texi
AM_V_HELP2MAN = $(AM_V_HELP2MAN_$(V))
AM_V_HELP2MAN_ = $(AM_V_HELP2MAN_$(AM_DEFAULT_VERBOSITY))
@@ -98,7 +99,6 @@ dist_man8_MANS = halt.8 reboot.8
# Things not automatically included in the distribution.
EXTRA_DIST = \
ChangeLog-2003 \
- fdl-1.3.texi \
QUESTIONS \
$(templates) \
doc/examples/README \
diff --git a/doc/fdl-1.3.texi b/doc/fdl-1.3.texi
new file mode 100644
index 0000000..cb71f05
--- /dev/null
+++ b/doc/fdl-1.3.texi
@@ -0,0 +1,505 @@
address@hidden The GNU Free Documentation License.
address@hidden Version 1.3, 3 November 2008
+
address@hidden This file is intended to be included within another document,
address@hidden hence no sectioning command or @node.
+
address@hidden
+Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation,
Inc.
address@hidden://fsf.org/}
+
+Everyone is permitted to copy and distribute verbatim copies
+of this license document, but changing it is not allowed.
address@hidden display
+
address@hidden 0
address@hidden
+PREAMBLE
+
+The purpose of this License is to make a manual, textbook, or other
+functional and useful document @dfn{free} in the sense of freedom: to
+assure everyone the effective freedom to copy and redistribute it,
+with or without modifying it, either commercially or noncommercially.
+Secondarily, this License preserves for the author and publisher a way
+to get credit for their work, while not being considered responsible
+for modifications made by others.
+
+This License is a kind of ``copyleft'', which means that derivative
+works of the document must themselves be free in the same sense. It
+complements the GNU General Public License, which is a copyleft
+license designed for free software.
+
+We have designed this License in order to use it for manuals for free
+software, because free software needs free documentation: a free
+program should come with manuals providing the same freedoms that the
+software does. But this License is not limited to software manuals;
+it can be used for any textual work, regardless of subject matter or
+whether it is published as a printed book. We recommend this License
+principally for works whose purpose is instruction or reference.
+
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+APPLICABILITY AND DEFINITIONS
+
+This License applies to any manual or other work, in any medium, that
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+A ``Modified Version'' of the Document means any work containing the
+Document or a portion of it, either copied verbatim, or with
+modifications and/or translated into another language.
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+The ``Invariant Sections'' are certain Secondary Sections whose titles
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+allowed to be designated as Invariant. The Document may contain zero
+Invariant Sections. If the Document does not identify any Invariant
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+The ``Cover Texts'' are certain short passages of text that are listed,
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address@hidden smallexample
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diff --git a/doc/shepherd.texi b/doc/shepherd.texi
new file mode 100644
index 0000000..5dc5f9c
--- /dev/null
+++ b/doc/shepherd.texi
@@ -0,0 +1,1593 @@
+\input texinfo @c -*- texinfo -*-
address@hidden shepherd.texi -- The documentation in Texinfo format.
address@hidden UTF-8
address@hidden shepherd.info
address@hidden The GNU Shepherd Manual
+
address@hidden version.texi
address@hidden OLD-YEARS 2002, 2003
address@hidden NEW-YEARS 2013, 2016
+
address@hidden
+Copyright @copyright{} @value{OLD-YEARS} Wolfgang J@"address@hidden
+Copyright @copyright{} @value{NEW-YEARS} Ludovic Courtès
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
+copy of the license is included in the section entitled ``GNU Free
+Documentation License''.
address@hidden copying
+
address@hidden System software
address@hidden
+* shepherd: (shepherd). The Shepherd service manager.
+* herd: (shepherd)Invoking herd
+ Controlling the Shepherd service manager.
+* reboot: (shepherd)Invoking reboot
+ Rebooting a Shepherd-controlled system.
+* halt: (shepherd)Invoking halt
+ Turning off a Shepherd-controlled system.
address@hidden direntry
+
address@hidden
address@hidden The GNU Shepherd Manual
address@hidden For use with the GNU Shepherd @value{VERSION}
address@hidden Last updated @value{UPDATED}
+
address@hidden Wolfgang J@"ahrling
address@hidden Ludovic Courtès
+
address@hidden
address@hidden titlepage
+
address@hidden
+
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden
address@hidden Top
address@hidden The GNU Shepherd Manual
+
+This manual documents the address@hidden version @value{VERSION}, a
+service manager for the GNU system.
+
address@hidden
+* Introduction:: Introduction to the Shepherd service manager.
+* Jump Start:: How to do simple things with the Shepherd.
+* herd and shepherd:: User interface to service management.
+* Services:: Details on services.
+* Runlevels:: Details on runlevels.
+* Misc Facilities:: Generally useful things provided by the Shepherd.
+* Internals:: Hacking shepherd.
+
+* GNU Free Documentation License:: The license of this manual.
+* Concept Index::
+* Procedure and Macro Index::
+* Variable Index::
+* Type Index::
address@hidden menu
address@hidden ifnottex
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Introduction
address@hidden Introduction
+
address@hidden service manager
+This manual documents the address@hidden Shepherd, or address@hidden
+for short. The Shepherd looks after system services, typically @dfn{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 @dfn{init system} of the GNU operating system---it is the
+first user process that gets started, typically with PID 1, and runs
+as @code{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
+(@pxref{Jump Start}). In chapter two we will describe the
address@hidden and @command{shepherd} programs, and their relationship, in
+more detail (@ref{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.
+
address@hidden dmd
+The Shepherd was formerly known as ``dmd'', which stands for @dfn{Daemon
+Managing Daemons} (or @dfn{Daemons-Managing Daemon}?).
+
address@hidden Guile
address@hidden Scheme
address@hidden GOOPS
+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.
address@hidden,,, guile, 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.
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Jump Start
address@hidden Jump Start
+
address@hidden prefix
+This chapter gives a short overview of the Shepherd. It is enough if you just
+need the basic features of it. As it is not assumed that readers are
+familiar with all the involved issues, a very experienced user might
+be annoyed by the often very detailed descriptions in this
+introduction. Those users are encouraged to just skip to the
+reference section.
+
+Note that all the full file names in the following text are based on
+the assumption that you have installed the Shepherd with an empty prefix. If
+your the Shepherd installation for example resides in @code{/usr/local}
+instead, add this directory name in front of the absolute file names
+mentioned below.
+
address@hidden Configuration file
+When @command{shepherd} gets started, it reads and evaluates a
+configuration file. When it is started with superuser priviledges, it
+tries to use @code{/etc/shepherd.scm}. When started as normal user, it
+looks for a file called @code{$XDG_CONFIG_HOME/shepherd/init.scm}. If
+the @code{XDG_CONFIG_HOME} environment variable is not defined,
address@hidden/.config/shepherd/init.scm} is used instead. With the option
address@hidden (or, for short, @code{-c}), you can specify where to
+look instead. So if you want to start @command{shepherd} with an
+alternative file, use one of the following commands:
+
address@hidden
+shepherd --config=/etc/shepherd.scm.old
+shepherd -c /etc/shepherd.scm.old
address@hidden example
+
address@hidden Starting a service
+As the final ``d'' suggests, @command{shepherd} is just
+a daemon that (usually) runs in the
+background, so you will not interact with it directly. After it is
+started, @command{shepherd} will listen on a socket special file, usually
address@hidden/var/run/shepherd/socket}, for further commands. You use the tool
address@hidden to send these commands to @command{shepherd}. Usage of herd is
simple and
+straightforward: To start a service called @code{apache}, you use:
+
address@hidden
+herd start apache
address@hidden example
+
address@hidden Status (of services)
address@hidden Service status
+When you do this, all its dependencies will get resolved. For
+example, a webserver is quite likely to depend on working networking,
+thus it will depend on a service called @code{networking}. So if you
+want to start @code{apache}, and @code{networking} is not yet running, it
+will automatically be started as well. The current status of all the
+services defined in the configuration file can be queried like this:
+
address@hidden
+herd status
address@hidden example
+
address@hidden
+Or, to get additional details about each service, run:
+
address@hidden
+herd detailed-status
address@hidden example
+
address@hidden
+In this example, this would show the @code{networking} and @code{apache}
+services as started. If you just want to know the status of the
address@hidden service, run:
+
address@hidden
+herd status apache
address@hidden example
+
address@hidden Stopping a service
+You can stop
+a service and all the services that depend on it will be stopped.
+Using the example above, if you stop @code{networking}, the service
address@hidden will be stopped as well---which makes perfect sense,
+as it cannot work without the network being up. To actually stop a
+service, you use the following, probably not very surprising, command:
+
address@hidden
+herd stop networking
address@hidden example
+
+There are two more actions you can perform on every service: The
+actions @code{enable} and @code{disable} are used to prevent and allow
+starting of the particular service. If a service is intended to be
+restarted whenever it terminates (how this can be done will not be
+covered in this introduction), but it is respawning too often in a
+short period of time (by default 5 times in 5 seconds), it will
+automatically be disabled. After you have fixed the problem that
+caused it from being respawned too fast, you can start it again with
+the commands:
+
address@hidden
+herd enable foo
+herd start foo
address@hidden example
+
address@hidden virtual services
address@hidden fallback services
+But there is far more you can do than just that. Services can not
+only simply depend on other services, they can also depend on
address@hidden services. A virtual service is a service that is
+provided by one or more service additionally. For instance, a service
+called @code{exim} might provide the virtual service
address@hidden That could as well be provided by a service
+called @code{smail}, as both are mailer-daemons. If a service needs
+any mailer-daemon, no matter which one, it can just depend on
address@hidden, and one of those who provide it gets started (if
+none is running yet) when resolving dependencies. The nice thing is
+that, if trying to start one of them fails, @command{shepherd} will go on and
try to
+start the next one, so you can also use virtual services for
+specifying @emph{fallbacks}.
+
+Additionally to all that, you can perform service-specific actions.
+Coming back to our original example, @code{apache} is able to
+reload its modules, therefore the action @code{reload-modules} might
+be available:
+
address@hidden
+herd reload-modules apache
address@hidden example
+
+The service-specific actions can only be used when the service is
+started, i.e. the only thing you can do to a stopped service is
+starting it. An exception exists, see below. (If you may at some
+point find this too restrictive because you want to use variants of
+the same service which are started in different ways, consider using
+different services for those variants instead, which all provide the
+same virtual service and thus conflict with each other, if this is
+desired. That's one of the reasons why virtual services exist, after
+all.)
+
+There are two actions which are special, because even if services
+can implement them on their own, a default implementation is provided
+by @command{shepherd} (another reason why they are special is that the default
+implementations can be called even when the service is not running;
+this inconsistency is just to make it more intuitive to get
+information about the status of a service, see below).
+
+These actions are @code{restart} and @code{status}. The default
+implementation of @code{restart} calls @code{stop} and @code{start} on
+the affected service in order, the @code{status} action displays some
+general information about the service, like what it provides, what it
+depends on and with which other services it conflicts (because they
+provide a virtual service that is also provided by that particular
+service).
+
+Another special action is @code{list-actions}, which displays a list
+of the additional actions a service provides; obviously, it can also
+be called when the service is not running. Services cannot provide
+their own implementation of @code{list-actions}.
+
+A special service is @code{root}, which is used for controlling the
+Shepherd itself. You can also reference to this service as
address@hidden It implements various actions. For example, the
address@hidden action displays which services are started and which ones
+are stopped, whereas @code{detailed-status} has the effect of applying
+the default implementation of @code{status} to all services one after
+another. The @code{load} action is unusual insofar as it shows a
+feature that is actually available to all services, but which we have
+not seen yet: It takes an additional argument. You can use @code{load}
+to load arbitrary code into the Shepherd at runtime, like this:
+
address@hidden
+herd load shepherd ~/additional-services.scm
address@hidden example
+
+This is enough now about the @command{herd} and @command{shepherd} programs, we
+will now take a look at how to configure the Shepherd. In the configuration
+file, we need mainly the definition of services. We can also do
+various other things there, like starting a few services already.
+
+FIXME: Finish. For now, look at the @code{examples/} subdirectory.
+
address@hidden
+...
address@hidden example
+
+Ok, to summarize:
+
address@hidden @bullet
address@hidden
address@hidden is a daemon, @command{herd} the program that controls it.
address@hidden
+You can start, stop, restart, enable and disable every service, as
+well as display its status.
address@hidden
+You can perform additional service-specific actions, which you can
+also list.
address@hidden
+Actions can have arguments.
address@hidden
+You can display the status of a service, even if the service does not
+provide a specific implementation for this action. The same is true
+for restarting.
address@hidden
+The @code{root}/@code{shepherd} service is used to control
address@hidden itself.
address@hidden itemize
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden herd and shepherd
address@hidden @command{herd} and @command{shepherd}
+
address@hidden herd
address@hidden shepherd
address@hidden daemon
address@hidden daemon controller
address@hidden relative file names
address@hidden herding, of daemons
+The daemon that runs in the background and is responsible for
+controlling the services is @command{shepherd}, while the user interface
+tool is called @command{herd}: it's the command that allows you to
+actually @emph{herd} your address@hidden
address@hidden deco, daemon controller
+In the past, when the
address@hidden was known as address@hidden, the @command{herd} command
+was called @code{deco}, for @dfn{DaEmon COntroller}.}. To perform an
+action, like stopping a service or calling an action of a service, you
+use the herd program. It will communicate with shepherd over a Unix
+Domain Socket.
+
+Thus, you start @command{shepherd} once, and then always use herd whenever you
want
+to do something service-related. Since herd passes its current
+working directory to @command{shepherd}, you can pass relative file names
without
+trouble. Both @command{shepherd} and herd understand the standard arguments
address@hidden, @code{--version} and @code{--usage}.
+
+
address@hidden
+* Invoking shepherd:: How to start the service damon.
+* Invoking herd:: Controlling daemons.
+* Invoking reboot:: Rebooting a shepherd-controlled system.
+* Invoking halt:: Turning off a shepherd-controlled system.
address@hidden menu
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Invoking shepherd
address@hidden Invoking @command{shepherd}
+
address@hidden @command{shepherd} Invocation
address@hidden invoking @command{shepherd}
+The @code{shepherd} program has the following synopsis:
+
address@hidden
+shepherd address@hidden@dots{}]
address@hidden example
+
+It accepts the following options:
+
address@hidden @samp
address@hidden -c @var{file}
address@hidden address@hidden
+Read and evaluate @var{file} as the configuration script on startup.
+
address@hidden is evaluated in the context of a fresh module where bindings
+from the @code{(shepherd service)} module and Guile's @code{(oop goops)} are
+available, in addition to the default set of Guile bindings. In
+particular, this means that code in @var{file} may use
address@hidden, the @code{<service>} class, and related tools
+(@pxref{Services}).
+
address@hidden -I
address@hidden --insecure
address@hidden security
address@hidden insecure
+Do not check if the directory where the socket---our communication
+rendez-vous with @command{herd}---is located has permissions @code{700}.
+If this option is not specified, @command{shepherd} will abort if the
+permissions are not as expected.
+
address@hidden -l address@hidden
address@hidden address@hidden
address@hidden logging
address@hidden log file
+Log output into @var{file}, or if @var{file} is not given,
address@hidden/var/log/shepherd.log} when running as superuser,
address@hidden/shepherd/shepherd.log} otherwise.
+
address@hidden address@hidden
+When @command{shepherd} is ready to accept connections, write its PID to
@var{file} or
+to the standard output if @var{file} is omitted.
+
address@hidden -p address@hidden
address@hidden address@hidden
address@hidden FIXME-CRITICAL
+
address@hidden -s @var{file}
address@hidden address@hidden
address@hidden socket special file
+Receive further commands on the socket special file @var{file}. If
+this option is not specified, @address@hidden/run/shepherd/socket} is
+taken.
+
+If @code{-} is specified as file name, commands will be read from
+standard input, one per line, as would be passed on a @command{herd}
+command line (@pxref{Invoking herd}).
+
address@hidden --quiet
+Synonym for @code{--silent}.
+
address@hidden table
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Invoking herd
address@hidden Invoking herd
+
address@hidden herd
+The @command{herd} command is a generic client program to control a
+running instance of @command{shepherd} (@pxref{Invoking shepherd}). It has the
+following synopsis:
+
address@hidden
+herd address@hidden@dots{}] @var{action} address@hidden address@hidden@dots{}]]
address@hidden example
+
+It causes the @var{action} of the @var{service} to be invoked. When
address@hidden is omitted and @var{action} is @code{status} or
address@hidden, the @code{root} service is address@hidden
+shorthand does not work for other actions such as @code{stop}, because
+inadvertently typing @code{herd stop} would stop all the services, which
+could be pretty annoying.} (@pxref{The root and unknown services}, for
+more information on the @code{root} service.)
+
+For each action, you should pass the appropriate @var{arg}s. Actions
+that are available for every service are @code{start}, @code{stop},
address@hidden, @code{status}, @code{enable}, @code{disable}, and
address@hidden
+
+If you pass a file name as an @var{arg}, it will be passed as-is to
+the Shepherd, thus if it is not an absolute name, it is local to the current
+working directory of @command{shepherd}, not to herd.
+
+The @code{herd} command understands the following option:
+
address@hidden @samp
+
address@hidden -s @var{file}
address@hidden address@hidden
+Send commands to the socket special file @var{file}. If this option is
+not specified, @address@hidden/run/shepherd/socket} is taken.
+
address@hidden table
+
+The @code{herd} command returns zero on success, and a non-zero exit
+code on failure. In particular, it returns a non-zero exit code when
address@hidden or @var{service} does not exist and when the given action
+failed.
+
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Invoking reboot
address@hidden Invoking reboot
+
address@hidden herd
+The @command{reboot} command is a convenience client program to instruct
+the Shepherd (when used as an init system) to stop all running services and
+reboot the system. It has the following synopsis:
+
address@hidden
+reboot address@hidden@dots{}]
address@hidden example
+
+It is equivalent to running @command{herd stop shepherd}. The
address@hidden command understands the following option:
+
address@hidden @samp
+
address@hidden -s @var{file}
address@hidden address@hidden
+Send commands to the socket special file @var{file}. If this option is
+not specified, @address@hidden/run/shepherd/socket} is taken.
+
address@hidden table
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Invoking halt
address@hidden Invoking halt
+
address@hidden herd
+The @command{halt} command is a convenience client program to instruct
+the Shepherd (when used as an init system) to stop all running services and
turn
+off the system. It has the following synopsis:
+
address@hidden
+halt address@hidden@dots{}]
address@hidden example
+
+It is equivalent to running @command{herd power-off shepherd}. As
+usual, the @code{halt} command understands the following option:
+
address@hidden @samp
+
address@hidden -s @var{file}
address@hidden address@hidden
+Send commands to the socket special file @var{file}. If this option is
+not specified, @address@hidden/run/shepherd/socket} is taken.
+
address@hidden table
+
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Services
address@hidden Services
+
address@hidden service
address@hidden <service>
+The @dfn{service} is obviously a very important concept of the Shepherd. On
the
+Guile level, a service is represented as an instance of
address@hidden<service>}, a GOOPS class (@pxref{GOOPS,,, guile, GNU Guile
+Reference Manual}). When creating an instance of it, you can specify
+the initial values of its slots, and you actually must do this for some
+of the slots.
+
+The @code{<service>} class and its associated procedures and methods are
+defined in the @code{(shepherd service)} module.
+
address@hidden
+* Slots of services:: What a <service> object consists of.
+* Methods of services:: What you can do with a <service> object.
+* Service Convenience:: How to conveniently work with services.
+* Service De- and Constructors:: Commonly used ways of starting and
+ stopping services.
+* Service Examples:: Examples that show how services are used.
+* The root and unknown services:: Special services in the Shepherd.
address@hidden menu
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Slots of services
address@hidden Slots of services
+
address@hidden <service>, slots of
address@hidden slots of <service>
+A service has the following slots, all of which can be initialized
+with a keyword (i.e. @code{#:provides}, used when creating the object)
+of the same name, except where stated otherwise. You should not
+access them directly with @code{slot-ref} or @code{slot-set!}
+usually, use the methods of the service class @ref{Methods of
+services} instead.
+
address@hidden @bullet
address@hidden
address@hidden provides (slot of <service>)
address@hidden canonical names of services
address@hidden is a list of symbols that are provided by the service.
+A symbol can only be provided by one service running at a time,
+i.e. if two services provide the same symbol, only one of them can
+run, starting the other one will fail. Therefore, these symbols are
+mainly used to denote conflicting services. The first symbol in the
+list is the canonical name for the service, thus it must be unique.
+This slot has no default value and must therefore be initialized.
+
address@hidden
address@hidden requires (slot of <service>)
address@hidden is, like @code{provides}, a list of symbols that
+specify services. In this case, they name what this service depends
+on, i.e. before the service can be started, services that provide
+those symbols must be started. If a required symbol is provided by
+several services, one will be started. By default, this slot
+contains the empty list.
+
address@hidden
address@hidden running (slot of <service>)
address@hidden Hook for individual services
address@hidden is a hook that can be used by each service in its own
+way. The default value is @code{#f}, which indicates that the service
+is not running. When an attempt is made to start the service, it will
+be set to the return value of the procedure in the @code{start} slot.
+It will also be passed as an argument to the procedure in the
address@hidden slot. This slot can not be initialized with a keyword.
+
address@hidden
address@hidden respawn? (slot of <service>)
address@hidden Respawning services
address@hidden specifies whether the service should be respawned by
+the Shepherd. If this slot has the value @code{#t}, then assume the
address@hidden slot specifies a child process PID and restart the
+service if that process terminates. Otherwise this slot is @code{#f},
+which is the default. See also the @code{last-respawns} slot.
+
address@hidden
address@hidden start (slot of <service>)
address@hidden Starting a service
address@hidden Service constructor
address@hidden contains the ``constructor'' for the service, which will
+be called to start the service. (Therefore, it is not a constructor
+in the sense that it initializes the slots of a @code{<service>}
+object.) This must be a procedure that accepts any amount of
+arguments, which will be the additional arguments supplied by the
+user. If the starting attempt failed, it must return @code{#f}. The
+value will be stored in the @code{running} slot. The default value is
+a procedure that returns @code{#t} and performs no further actions,
+therefore it is desirable to specify a different one usually.
+
address@hidden
address@hidden stop (slot of <service>)
address@hidden Stoping a service
address@hidden Service destructor
address@hidden is, similar to @code{start}, a slot containing a
+procedure. But in this case, it gets the current value of the
address@hidden slot as first argument and the user-supplied arguments
+as further arguments; it gets called to stop the service. Its return
+value will again be stored in the @code{running} slot, so that it
+should return @code{#f} if it is now possible again to start the
+service at a later point. The default value is a procedure that
+returns @code{#f} and performs no further actions.
+
address@hidden
address@hidden actions (slot of <service>)
address@hidden Actions of services
address@hidden Service actions
address@hidden specifies the additional actions that can be performed
+on a service when it is running. A typical example for this is the
address@hidden action. The macro @code{make-actions} @ref{Service
+Convenience} is provided to abstract the actual data representation
+format for this slot. (It actually is a hash currently.)
+
address@hidden
address@hidden enabled? (slot of <service>)
address@hidden cannot be initialized with a keyword, and contains
address@hidden by default. When the value becomes @code{#f} at some point,
+this will prevent the service from getting started. A service can be
+enabled and disabled with the methods @code{enable} and
address@hidden, respectively @ref{Methods of services}.
+
address@hidden
address@hidden last-respawns (slot of <service>)
address@hidden cannot be initialized with a keyword and is only
+ever used when the @code{respawn?} slot contains @code{#t}; it is a
+circular list with @code{(car respawn-limit)} elements, where each
+element contains the time when it was restarted, initially all 0,
+later a time in seconds since the Epoch. The first element is the one
+that contains the oldest one, the last one the newest.
+
address@hidden
address@hidden stop-delay? (slot of <service>)
address@hidden being false causes the @code{stop} slot to be
+unused; instead, stopping the service will just cause the
address@hidden slot be set to @code{#t}.
+
address@hidden
address@hidden waiting-for-termination? (slot of <service>)
address@hidden cannot be initialized with a keyword
+and should not be used by others, it is only used internally for
+respawnable services when the @code{stop-delay?} slot contains a true
+value. @code{waiting-for-termination?} contains @code{#t} if the
+service is still running, but the user requested that it be stopped,
+in which case if the service terminates the next time, the respawn
+handler will not start it again.
+
+otherwise @code{#f}.
+
address@hidden itemize
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Methods of services
address@hidden Methods of services
+
address@hidden {method} start (obj <service>)
+Start the service @var{obj}, including all the services it depends on.
+It tries quite hard to do this: When a service that provides a
+required symbol can not be started, it will look for another service
+that also provides this symbol, until starting one such service
+succeeds. There is some room for theoretical improvement here, of
+course, but in pratice the current strategy already works very well.
+This method returns the new value of the @code{running} slot
address@hidden of services}, which is @code{#f} if the service could not
+be started.
address@hidden deffn
+
address@hidden {method} stop (obj <service>)
+This will stop the service @var{obj}, trying to stop services that
+depend in it first, so they can be shutdown cleanly. If this will
+fail, it will continue anyway. Stopping of services should usually
+succeed, though. Otherwise, the behaviour is very similar to the
address@hidden method. The return value is also the new @code{running}
+value, thus @code{#f} if the service was stopped.
address@hidden deffn
+
address@hidden {method} action (obj <service>) the-action . args
+Calls the action @var{the-action} (a symbol) of the service @var{obj},
+with the specified @var{args}, which have a meaning depending on the
+particular action.
address@hidden deffn
+
address@hidden {method} conflicts-with (obj <service>)
+Returns a list of the canonical names of services that conflict with
+the service @var{obj}.
address@hidden deffn
+
address@hidden {method} canonical-name (obj <service>)
+Returns the canonical name of @var{obj}, which is the first element of
+the @code{provides} list.
address@hidden deffn
+
address@hidden {method} provided-by (obj <service>)
+Returns which symbols are provided by @var{obj}.
address@hidden deffn
+
address@hidden {method} required-by (obj <service>)
+Returns which symbols are required by @var{obj}.
address@hidden deffn
+
address@hidden {method} running? (obj <service>)
+Returns whether the service @var{obj} is running.
address@hidden deffn
+
address@hidden {method} respawn? (obj <service>)
+Returns whether the service @var{obj} should be respawned if it
+terminates.
address@hidden deffn
+
address@hidden {method} default-display-status (obj <service>)
+Display status information about @var{obj}. This method is called
+when the user performs the action @code{status} on @var{obj}, but
+there is no specific implementation given for it. It is also called
+when @code{detailed-status} is applied on the @code{root} service.
address@hidden deffn
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Service Convenience
address@hidden Service Convenience
+
+In addition to the facilities listed below, there are also some
+procedures that provide commonly needed constructors and destructors
+for services @ref{Service De- and Constructors}.
+
address@hidden {procedure} register-services . services
+Register all @var{services}, so that they can be taken into account
+when trying to resolve dependencies.
address@hidden deffn
+
address@hidden {procedure} lookup-services name
+Return a list of all registered services which provide the symbol
address@hidden
address@hidden deffn
+
address@hidden {macro} make-actions (name proc) ...
+This macro is used to create a value for the @code{actions} slot of a
+service object @ref{Slots of services}. Each @var{name} is a symbol
+and each @var{proc} the corresponding procedure that will be called to
+perform the action. A @var{proc} has one argument, which will be the
+current value of the @code{running} slot of the service.
address@hidden deffn
+
address@hidden {method} start (obj <symbol>)
+Start a registered service providing @var{obj}.
address@hidden deffn
+
address@hidden {method} stop (obj <symbol>)
+Stop a registered service providing @var{obj}.
address@hidden deffn
+
address@hidden {method} action (obj <symbol>) the-action . args
+The same as the @code{action} method of class @code{<service>}, but
+uses a service that provides @var{obj} and is running.
address@hidden deffn
+
address@hidden {procedure} for-each-service proc
+Call @var{proc}, a procedure taking one argument, once for each
+registered service.
address@hidden deffn
+
address@hidden {procedure} find-running services
+Check if any of @var{services} is running. If this is the case,
+return its canonical name. If not, return @code{#f}. Only the first
+one will be returned; this is because this is mainly intended to be
+applied on the return value of @code{lookup-services}.
address@hidden deffn
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Service De- and Constructors
address@hidden Service De- and Constructors
+
address@hidden generating constructors
address@hidden generating destructors
address@hidden constructors, generation of
address@hidden destructors, generation of
+All of the procedures listed below return procedures generated from
+the supplied arguments. These procedures take one argument in the
+case of destructors and no arguments in the case of constructors.
+
address@hidden {procedure} make-system-constructor @address@hidden
+The returned procedure will execute @var{command} in a shell and
+return @code{#t} if execution was successful, otherwise @code{#f}.
+For convenience, it takes multiple arguments which will be
+concatenated first.
address@hidden deffn
+
address@hidden {procedure} make-system-destructor @address@hidden
+Similar to @code{make-system-constructor}, but returns @code{#f} if
+execution of the @var{command} was successful, @code{#t} if not.
address@hidden deffn
+
address@hidden {procedure} make-forkexec-constructor @var{command} @
+ [#:user #f] @
+ [#:group #f] @
+ [#:pid-file #f] @
+ [#:directory (default-service-directory)] @
+ [#:environment-variables (default-environment-variables)]
+Return a procedure that forks a child process, closes all file
+descriptors except the standard output and standard error descriptors, sets
+the current directory to @var{directory}, changes the environment to
address@hidden (using the @code{environ} procedure), sets the
+current user to @var{user} and the current group to @var{group} unless they
+are @code{#f}, and executes @var{command} (a list of strings.) The result of
+the procedure will be the PID of the child process.
+
+When @var{pid-file} is true, it must be the name of a PID file
+associated with the process being launched; the return value is the PID
+read from that file, once that file has been created.
address@hidden deffn
+
address@hidden {procedure} make-kill-destructor address@hidden
+Returns a procedure that sends @var{signal} to the pid which it takes
+as argument. This @emph{does} work together with respawning services,
+because in that case the @code{stop} method of the @code{<service>}
+class sets the @code{running} slot to @code{#f} before actually
+calling the destructor; if it would not do that, killing the process
+in the destructor would immediately respawn the service.
address@hidden deffn
+
+The @code{make-forkexec-constructor} procedure builds upon the following
+procedures.
+
address@hidden {procedure} exec-command @var{command} @
+ [#:user #f] @
+ [#:group #f] @
+ [#:directory (default-service-directory)] @
+ [#:environment-variables (default-environment-variables)]
address@hidden {procedure} fork+exec-command @var{command} @
+ [#:user #f] @
+ [#:group #f] @
+ [#:directory (default-service-directory)] @
+ [#:environment-variables (default-environment-variables)]
+Run @var{command} as the current process from @var{directory}, and with
address@hidden (a list of strings like @code{"PATH=/bin"}.)
+File descriptors 1 and 2 are kept as is, whereas file descriptor 0
+(standard input) points to @file{/dev/null}; all other file descriptors
+are closed prior to yielding control to @var{command}.
+
+By default, @var{command} is run as the current user. If the
address@hidden keyword argument is present and not false, change to
address@hidden immediately before invoking @var{command}. @var{user} may
+be a string, indicating a user name, or a number, indicating a user
+ID. Likewise, @var{command} will be run under the current group,
+unless the @var{group} keyword argument is present and not false.
+
address@hidden does the same as @code{exec-command}, but in
+a separate process whose PID it returns.
address@hidden deffn
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Service Examples
address@hidden Service Examples
+
+FIXME: This needs a lot of work.
+
+You can create a service and then register it this way:
+
address@hidden
+(define apache (make <service>
+ #:provides '(apache)
+ #:start (...)
+ #:stop (...)))
+(register-services apache)
address@hidden lisp
+
+However, as you usually won't need a variable for the service, you can
+pass it directly to @code{register-services}. Here is an example that
+also specifies some more initial values for the slots:
+
address@hidden
+(register-services
+ (make <service>
+ #:provides '(apache-2.0 apache httpd)
+ #:requires '()
+ #:start (...)
+ #:stop (...)
+ #:actions (make-actions
+ (reload-modules (...))
+ (restart (...)))))
address@hidden lisp
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden The root and unknown services
address@hidden The @code{root} and @code{unknown} services
+
address@hidden root service
address@hidden special services
+The service @code{root} is special, because it is used to control the
+Shepherd itself. It has an alias @code{shepherd}. It provides the
+following actions (in addition to @code{enable}, @code{disable} and
address@hidden which do not make sense here).
+
address@hidden @code
address@hidden status
+Displays which services are started and which ones are not.
+
address@hidden detailed-status
+Displays detailed information about every registered service.
+
address@hidden load @var{file}
+Evaluate the Scheme code in @var{file} in a fresh module that uses the
address@hidden(oop goops)} and @code{(shepherd services)} modules---as with the
address@hidden option of @command{shepherd} (@pxref{Invoking shepherd}).
+
address@hidden unload @var{service-name}
+Attempt to remove the service identified by @var{service-name}.
address@hidden will first stop the service, if necessary, and then
+remove it from the list of registered services. Any services
+depending upon @var{service-name} will be stopped as part of this
+process.
+
+If @var{service-name} simply does not exist, output a warning and do
+nothing. If it exists, but is provided by several services, output a
+warning and do nothing. This latter case might occur for instance with
+the fictional service @code{web-server}, which might be provided by both
address@hidden and @code{nginx}. If @var{service-name} is the special
+string and @code{all}, attempt to remove all services except for the Shepherd
+itself.
+
address@hidden reload @var{file-name}
+Unload all known optional services using unload's @code{all} option,
+then load @var{file-name} using @code{load} functionality. If
+file-name does not exist or @code{load} encounters an error, you may
+end up with no defined services. As these can be reloaded at a later
+stage this is not considered a problem. If the @code{unload} stage
+fails, @code{reload} will not attempt to load @var{file-name}.
+
address@hidden daemonize
+Fork and go into the background. This should be called before
+respawnable services are started, as otherwise we would not get the
address@hidden signals when they terminate.
+
address@hidden enable-persistency
+When terminating, safe the list of running services in a file.
address@hidden FIXME-CRITICAL: How can we specify which one?
+
address@hidden disable-persistency
+Don't safe the list of running services when terminating.
+
address@hidden table
+
address@hidden unknown service
address@hidden fallback service
+The @code{unknown} service must be defined by the user and if it
+exists, is used as a fallback whenever we try to invoke an unknown
+action of an existing service or use a service that does not exist.
+This is useful only in few cases, but enables you to do various sorts
+of unusual things.
+
address@hidden FIXME-CRITICAL: finish
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Runlevels
address@hidden Runlevels
+
+RUNLEVELS DO NOT WORK YET! Do not use them! Ignore this section!
+
address@hidden runlevel
address@hidden <runlevel>
+A @dfn{runlevel} makes it easier to start and stop groups of services,
+to bring the system into a certain state. An object of class
address@hidden<runlevel>} is an abstract runlevel, and has the following
+methods:
+
address@hidden {method} enter (rl <runlevel>) services
+This will be called when the runlevel should be entered.
address@hidden is the list of the currently running services.
address@hidden deffn
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Misc Facilities
address@hidden Misc Facilities
+
+This is a list of facilities which are available to code running
+inside of the Shepherd and is considered generally useful, but is not directly
+related to one of the other topic covered in this manual.
+
address@hidden
+* Errors:: Signalling, handling and ignoring errors.
+* Communication:: Input/Output in various ways.
+* Others:: Stuff that is useful, but is homeless.
address@hidden menu
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Errors
address@hidden Errors
+
address@hidden assertions
address@hidden {macro} assert expr
+If @var{expr} yields @code{#f}, display an appropriate error
+message and throw an @code{assertion-failed} exception.
address@hidden deffn
+
address@hidden {procedure} caught-error key args
+Tell the Shepherd that a @var{key} error with @var{args} has occured. This is
+the simplest way to cause caught error result in uniformly formated
+warning messages. The current implementation is not very good,
+though.
address@hidden deffn
+
address@hidden {procedure} call/cc proc
+An alias for @code{call-with-current-continuation}.
address@hidden deffn
+
address@hidden {procedure} call/ec proc
+A simplistic implementation of the nonstandard, but popular procedure
address@hidden, i.e. a @code{call/cc} for
+outgoing continuations only. Note that the variant included in the Shepherd is
+not aware of @code{dynamic-wind} at all and does not yet support
+returning multiple values.
address@hidden deffn
+
address@hidden system errors
address@hidden {macro} without-system-error address@hidden
+Evaluates the @var{expr}s, not going further if a system error occurs,
+but also doing nothing about it.
address@hidden deffn
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Communication
address@hidden Communication
+
+The @code{(shepherd comm)} module provides primitives that allow clients such
+as @command{herd} to connect to @command{shepherd} and send it commands to
+control or change its behavior (@pxref{Slots of services, actions of
+services}).
+
address@hidden <shepherd-command>
+Currently, clients may only send @dfn{commands}, represented by the
address@hidden<shepherd-command>} type. Each command specifies a service it
+applies to, an action name, a list of strings to be used as arguments,
+and a working directory. Commands are instantiated with
address@hidden:
+
address@hidden {procedure} shepherd-command @var{action} @var{service} @
+ [#:@var{arguments} '()] [#:@var{directory} (getcwd)]
+Return a new command (a @code{<shepherd-command>}) object for
address@hidden on @var{service}.
address@hidden deffn
+
address@hidden
+Commands may then be written to or read from a communication channel
+with the following procedures:
+
address@hidden {procedure} write-command @var{command} @var{port}
+Write @var{command} to @var{port}.
address@hidden deffn
+
address@hidden {procedure} read-command @var{port}
+Receive a command from @var{port} and return it.
address@hidden deffn
+
+In practice, communication with @command{shepherd} takes place over a
+Unix-domain socket, as discussed earlier (@pxref{Invoking shepherd}).
+Clients may open a connection with the procedure below.
+
address@hidden {procedure} open-connection address@hidden
+Open a connection to the daemon, using the Unix-domain socket at
address@hidden, and return the socket.
+
+When @var{file} is omitted, the default socket is used.
address@hidden deffn
+
address@hidden output
+The daemon writes output to be logged or passed to the
+currently-connected client using @code{local-output}:
+
address@hidden {procedure} local-output format-string . args
+This procedure should be used for all output operations in the Shepherd. It
+outputs the @var{args} according to the @var{format-string}, then
+inserts a newline. It writes to whatever is the main output target of
+the Shepherd, which might be multiple at the same time in future versions.
address@hidden deffn
+
address@hidden protocol, between @command{shepherd} and its clients
+Under the hood, @code{write-command} and @code{read-command} write/read
+commands as s-expressions (sexps). Each sexp is intelligible and
+specifies a protocol version. The idea is that users can write their
+own clients rather than having to invoke @command{herd}. For instance,
+when you type @command{herd status}, what is sent over the wire is the
+following sexp:
+
address@hidden
+(shepherd-command
+ (version 0)
+ (action status) (service root)
+ (arguments ()) (directory "/data/src/dmd"))
address@hidden lisp
+
+The reply is also an sexp, along these lines:
+
address@hidden
+(reply (version 0)
+ (result (((service @dots{}) @dots{})))
+ (error #f) (messages ()))
address@hidden lisp
+
+This reply indicates that the @code{status} action was successful,
+because @code{error} is @code{#f}, and gives a list of sexps denoting
+the status of services as its @code{result}. The @code{messages} field
+is a possibly-empty list of strings meant to be displayed as is to the
+user.
+
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Others
address@hidden Others
+
address@hidden hashes
address@hidden {procedure} copy-hashq-table table new-size
+Create a hash-table with size @var{new-size}, and insert all values
+from @var{table} into it, using @code{eq?} when inserting. This
+procedure is mainly used internally, but is a generally useful
+utillity, so it can by used by everyone.
address@hidden deffn
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Internals
address@hidden Internals
+
+This chapter contains information about the design and the
+implementation details of the Shepherd for people who want to hack it.
+
+The address@hidden is developed by a group of people in connection
+with @uref{https://www.gnu.org/software/guix/, GuixSD}, GNU's advanced
+distribution, but it can be used on other distros as well. You're very
+much welcome to join us! You can report bugs to
address@hidden@@gnu.org} and send patches or suggestions to
address@hidden@@gnu.org}.
+
address@hidden
+* Coding standards:: How to properly hack the Shepherd.
+* Design decisions:: Why the Shepherd is what it is.
+* Service Internals:: How services actually work.
+* Runlevel evolution:: Learning from past mistakes.
address@hidden menu
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Coding standards
address@hidden Coding standards
+
+About formatting: Use common sense and GNU Emacs (which actually is
+the same, of course), and you almost can't get the formatting wrong.
+Formatting should be as in Guile and Guix, basically. @xref{Coding
+Style,,, guix, GNU Guix Reference Manual}, for more info.
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Design decisions
address@hidden Design decisions
+
address@hidden Note
+This section was written by Wolfgang Jährling back in 2003 and documents
+the original design of what was then known as address@hidden The main
+ideas remain valid but some implementation details and goals have
+changed.
address@hidden quotation
+
+The general idea of a service manager that uses dependencies, similar
+to those of a Makefile, came from the developers of the GNU Hurd, but
+as few people are satisfied with System V Init, many other people had
+the same idea independently. Nevertheless, the Shepherd was written with the
+goal of becoming a replacement for System V Init on GNU/Hurd, which
+was one of the reasons for choosing the extension language of the GNU
+project, Guile, for implementation (another reason being that it makes
+it just so much easier).
+
+The runlevel concept (i.e. thinking in @emph{groups} of services) is
+sometimes useful, but often one also wants to operate on single
+services. System V Init makes this hard: While you can start and stop
+a service, @code{init} will not know about it, and use the runlevel
+configuration as its source of information, opening the door for
+inconsistencies (which fortunatly are not a practical problem
+usually). In the Shepherd, this was avoided by having a central entity that is
+responsible for starting and stopping the services, which therefore
+knows which services are actually started (if not completely
+inproperly used, but that is a requirement which is impossible to
+avoid anyway). While runlevels are not implemented yet, it is clear
+that they will sit on top of the service concept, i.e. runlevels will
+merely be an optional extension that the service concept does not rely
+on. This also makes changes in the runlevel design easier when it may
+become necessary.
+
+The consequence of having a daemon running that controls the services
+is that we need another program as user interface which communicates
+with the daemon. Fortunatly, this makes the commands necessary for
+controlling services pretty short and intuitive, and gives the
+additional bonus of adding some more flexibility. For example, it is
+easiely possible to grant password-protected control over certain
+services to unprivileged users, if desired.
+
+An essential aspect of the design of the Shepherd (which was already mentioned
+above) is that it should always know exactly what is happening,
+i.e. which services are started and stopped. The alternative would
+have been to not use a daemon, but to save the state on the file
+system, again opening the door for inconsistencies of all sorts.
+Also, we would have to use a seperate program for respawning a service
+(which just starts the services, waits until it terminates and then
+starts it again). Killing the program that does the respawning (but
+not the service that is supposed to be respawned) would cause horrible
+confusion. My understanding of ``The Right Thing'' is that this
+conceptionally limited strategy is exactly what we do not want.
+
+The way dependencies work in the Shepherd took a while to mature, as it was not
+easy to figure out what is appropriate. I decided to not make it too
+sophisticated by trying to guess what the user might want just to
+theoretically fulfill the request we are processing. If something
+goes wrong, it is usually better to tell the user about the problem
+and let her fix it, taking care to make finding solutions or
+workarounds for problems (like a misconfigured service) easy. This
+way, the user is in control of what happens and we can keep the
+implementation simple. To make a long story short, @emph{we don't try
+to be too clever}, which is usually a good idea in developing
+software.
+
+If you wonder why I was giving a ``misconfigured service'' as an
+example above, consider the following situation, which actually is a
+wonderful example for what was said in the previous paragraph: Service
+X depends on symbol S, which is provided by both A and B. A depends
+on AA, B depends on BB. AA and BB conflict with each other. The
+configuration of A contains an error, which will prevent it from
+starting; no service is running, but we want to start X now. In
+resolving its dependencies, we first try to start A, which will cause
+AA to be started. After this is done, the attempt of starting A
+fails, so we go on to B, but its dependency BB will fail to start
+because it conflicts with the running service AA. So we fail to
+provide S, thus X cannot be started. There are several possibilities
+to deal with this:
+
address@hidden @bullet
address@hidden
+When starting A fails, terminate those services which have been
+started in order to fulfill its dependencies (directly and
+indirectly). In case AA was running already, we would not want to
+terminate it. Well, maybe we would, to avoid the conflict with BB.
+But even if we would find out somehow that we need to terminate AA to
+eventually start X, is the user aware of this and wants this to happen
+(assuming AA was running already)? Probably not, she very likely has
+assumed that starting A succeeds and thus terminating AA is not
+necessary. Remember, unrelated (running) services might depend in AA.
+Even if we ignore this issue, this strategy is not only complicated,
+but also far from being perfect: Let's assume starting A succeeds, but
+X also depends on a service Z, which requires BB. In that case, we
+would need to detect in the first place that we should not even try to
+start A, but directly satisfy X's dependency on S with B.
+
address@hidden
+We could do it like stated above, but stop AA only if we know we won't
+need it anymore (for resolving further dependencies), and start it
+only when it does not conflict with anything that needs to get
+started. But should we stop it if it conflicts with something that
address@hidden get started? (We do not always know for sure what we
+will start, as starting a service might fail and we want to fall back
+to a service that also provides the particular required symbol in that
+case.) I think that either decision will be bad in one case or
+another, even if this solution is already horribly complicated.
+
address@hidden
+When we are at it, we could just calculate a desired end-position, and
+try to get there by starting (and stopping!) services, recalculating
+what needs to be done whenever starting a service fails, also marking
+that particular service as unstartable, except if it fails to start
+because a dependency could not be resolved (or maybe even then?).
+This is even more complicated. Instead of implementing this and
+thereby producing code that (a) nobody understands, (b) certainly has
+a lot of bugs, (c) will be unmaintainable and (d) causes users to
+panic because they won't understand what will happen, I decided to do
+the following instead:
+
address@hidden
+Just report the error, and let the user fix it (in this case, fix the
+configuration of A) or work around it (in this case, disable A so that
+we won't start AA but directly go on to starting B).
address@hidden itemize
+
+I hope you can agree that the latter solution after all is the best
+one, because we can be sure to not do something that the user does not
+want us to do. Software should not run amok. This explanation was
+very long, but I think it was necessary to justify why the Shepherd uses a very
+primitive algorithm to resolve dependencies, despite the fact that it
+could theoretically be a bit more clever in certain situations.
+
+One might argue that it is possible to ask the user if the planned
+actions are ok with her, and if the plan changes ask again, but
+especially given that services are supposed to usually work, I see few
+reasons to make the source code of the Shepherd more complicated than
+necessary. If you volunteer to write @emph{and} maintain a more
+clever strategy (and volunteer to explain it to everyone who wants to
+understand it), you are welcome to do so, of address@hidden
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Service Internals
address@hidden Service Internals
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Runlevel evolution
address@hidden Runlevel evolution
+
address@hidden Note
+This section was written by Wolfgang Jährling back in 2003 and is kept
+mostly for historians to read.
address@hidden quotation
+
+This section describes how the runlevel concept evolved over time.
+This is basically a collection of mistakes, but is provided here for
+your information, and possibly for your amusement, but I'm not sure if
+all this weird dependency stuff is really that funny.
+
address@hidden
+* Runlevel assumptions:: What runlevels should be like
+* Runlevels - part one:: The first attempts of making it work
+* Runlevels - part two:: It should work... somehow...
address@hidden menu
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Runlevel assumptions
address@hidden Runlevel assumptions
+
+A runlevel is a system state, i.e. it consists of the information
+about which services are supposed to be available and which not. This
+vague definition implies that several different runlevel styles can be
+implemented in a service manager.
+
+For example, you can do it like System V Init, specifying which
+services should be started when we enter a runlevel and which ones
+should be stopped when leaving it. But one could also specify for
+every service in which runlevels it should be running.
+
+In the Shepherd, we do not want to limit ourselfes to a single runlevel style.
+We allow for all possible strategies to be implemented, providing the
+most useful ones as defaults. We also want to make it possible to
+combine the different styles arbitrariely.
+
+Therefore, when entering a runlevel, we call a user-defined piece of
+code, passing it the list of currently active services and expecting
+as the result a list of service symbols which tell us which services
+we want to have running. This interface makes it very easy to
+implement runlevel styles, but makes it not-so-easy for the runlevel
+implementation itself, because we have to get from the current state
+into a desired state, which might be more or less vague (since it is
+not required to be a list of canonical names). Obviously service
+conflicts and already running services need to be taken into account
+when deciding which services should be used to provide the various
+symbols.
+
+Also, the runlevel implementation should be implemented completely on
+top of the service concept, i.e. the service part should not depend on
+the idea of runlevels or care about them at all. Otherwise
+understanding the service part (which is the most essential aspect of
+the Shepherd) would become harder than necessary.
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Runlevels - part one
address@hidden Runlevels, part one
+
+I came up with the following method (here in Pseudo-Scheme), which is
+possibly slightly buggy, but should give you the idea:
+
address@hidden
+;; Beginning with the canonical names in CURRENT-SERVICES, start and
+;; stop services until getting into a state where everything requested
+;; in TARGET-SERVICES (which does not only consist of canonical names)
+;; is provided, and the things they depends on, but no more.
+(define (switch-runlevel current-services target-services)
+ (let ((target-services-backup target-services)
+ (unstartable '()))
+ (let retry ()
+ (repeat-until-none-of-these-changes-annythig
+ ;; Replace all of them with canonical names which provide them.
+ (canonicalize-names! target-services unstartable current-services)
+ ;; Add what we need additionally.
+ (add-dependencies! target-services unstartable current-services))
+ (remove-redundancy! target-services)
+ (stop-all-unneeded target-services)
+ (catch 'service-could-not-be-started
+ (lambda ()
+ ;; Iterate over the list, starting only those which
+ ;; have all dependencies already resolved, so nothing
+ ;; we don't want will be started. Repeat until done.
+ (carefully-start target-services))
+ (lambda (key service)
+ (set! unstartable (cons service unstartable))
+ (set! target-services backup-target-services)
+ (set! current-services (compute-current-services))
+ (retry))))))
address@hidden lisp
+
+This indeed looks like a nice way to get what we want. However, the
+details of this are not as easy as it looks like. When replacing
+virtual services with canonical names, we have to be very careful.
+Consider the following situation:
+
+The virtual service X is provided by both A and B, while Y is provided
+only by B. We want to start C (which depends on X) and D (which
+depends on Y). Obviously we should use B to fulfill the dependency
+of C and D on X and Y, respectively. But when we see that we need
+something that provides X, we are likely to do the wrong thing: Select
+A. Thus, we need to clean this up later. I wanted to do this as
+follows:
+
+While substituting virtual services with canonical names, we also safe
+which one we selected to fulfill what, like this:
+
address@hidden
+((A . (X))
+ (B . (Y)))
address@hidden lisp
+
+Later we look for conflicts, and as A and B conflict, we look which
+one can be removed (things they provide but are not required by anyone
+should be ignored, thus we need to create a list like the above). In
+this case, we can replace A with B as B also provides X (but A does
+not provide Y, thus the reverse is impossible). If both could be
+used, we probably should decide which one to use by looking at further
+conflicts, which gets pretty hairy. But, in this case, we are lucky
+and end up with this:
+
address@hidden
+((B . (X Y)))
address@hidden lisp
+
+This way of finding out which service we should use in case of
+conflicts sounds pretty sane, but if you think it will work well, you
+have been fooled, because actually it breaks horribly in the following
+situation:
+
address@hidden @columnfractions .10 .30
address@hidden Service @tab Provides
address@hidden A @tab @code{W X Y -}
address@hidden B @tab @code{W X - Z}
address@hidden C @tab @code{- X Y Z}
address@hidden D @tab @code{W - - -}
address@hidden multitable
+
+If we need all of W, X, Y and Z, then obviously we need to take C and
+D. But if we have a list like this, we cannot fix it:
+
address@hidden
+((A . (W X Y))
+ (B . (Z)))
address@hidden lisp
+
+Thus, we cannot do it this way.
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Runlevels - part two
address@hidden Runlevels, part two
+
+Let's look again at the table at the end of part two:
+
address@hidden @columnfractions .10 .30
address@hidden Service @tab Provides
address@hidden A @tab @code{W X Y -}
address@hidden B @tab @code{W X - Z}
address@hidden C @tab @code{- X Y Z}
address@hidden D @tab @code{W - - -}
address@hidden multitable
+
+If from this table it is so obvious for us what we should do, then it
+should also be possible to calculate it for a computer, given such a
+table as input. Ok, we have to take into account conflicts that are
+not visible in this table, but the general idea is usable. But how do
+we find which combination works? I found only one way yet: Kind of a
+brute force attack: Try combinations until we find one that works.
+
+This alone would be too slow. With 20 services we would have 2^20
+possible combinations, that is a bit more than a million. Fortunatly,
+we can optimize this. First I thought we could remove all services
+from the list that do not provide any symbol we need, but that is
+obviously a stupid idea, as we might need them for dependencies, in
+which case we need to take into account their conflicts. But the
+following method would work:
+
+Very often a symbol that is required will be a canonical name already,
+i.e. be provided only by a single service. Using our example above,
+let's suppose we also need the symbol V, which is provided only by D.
+The first step we do is to look which (required) symbols are provided
+only by a single service, as we will need this service for sure. In
+this case, we would need D. But by using it, we would also get the
+other symbols it provides, W in this case. This means that we don't
+need to bother looking at other services that provide W, as we cannot
+use them because they conflict with a service that we definitely need.
+In this case, we can remove A and B from the list this way. Note that
+we can remove them entirely, as all their conflicts become irrelevant
+to us now. In this simple case we would not even have to do much
+else, C is the only remaining service.
+
+After this first step, there remain the symbols that are provided by
+two or more services. In every combination we try, exactly one of
+them must be used (and somehow we should take into account which
+services are running already). This also reduces the amount of
+possible combinations a lot. So what remains after that are the
+services we might need for fulfilling dependencies. For them, we
+could try all combinations (2^n), making sure that we always try
+subsets before any of their supersets to avoid starting unneeded
+services. We should take into account which services are already
+running as well.
+
+The remaining question is, what to do if starting a service fails. A
+simple solution would be to recursively remove all services that
+depend on it directly or indirectly. That might cause undesired
+side-effects, if a service was running but it had to be stopped
+because one of the services that provides something it depends on gets
+exchanged for another service that provides the same symbol, but fails
+to start. The fact that we would have to stop the (first) service is
+a problem on its own, though.
+
+
address@hidden
*********************************************************************
address@hidden GNU Free Documentation License
address@hidden GNU Free Documentation License
+
address@hidden fdl-1.3.texi
+
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
address@hidden Concept Index
address@hidden Concept Index
+
address@hidden cp
+
address@hidden Procedure and Macro Index
address@hidden Procedure and Macro Index
+
address@hidden fn
+
address@hidden Variable Index
address@hidden Variable Index
+
address@hidden vr
+
address@hidden Type Index
address@hidden Type Index
+
address@hidden tp
+
address@hidden
diff --git a/fdl-1.3.texi b/fdl-1.3.texi
deleted file mode 100644
index cb71f05..0000000
--- a/fdl-1.3.texi
+++ /dev/null
@@ -1,505 +0,0 @@
address@hidden The GNU Free Documentation License.
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-The Free Software Foundation may publish new, revised versions
-of the GNU Free Documentation License from time to time. Such new
-versions will be similar in spirit to the present version, but may
-differ in detail to address new problems or concerns. See
address@hidden://www.gnu.org/copyleft/}.
-
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-If the Document specifies that a particular numbered version of this
-License ``or any later version'' applies to it, you have the option of
-following the terms and conditions either of that specified version or
-of any later version that has been published (not as a draft) by the
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-number of this License, you may choose any version ever published (not
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-An MMC is ``eligible for relicensing'' if it is licensed under this
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-under CC-BY-SA on the same site at any time before August 1, 2009,
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address@hidden enumerate
-
address@hidden
address@hidden ADDENDUM: How to use this License for your documents
-
-To use this License in a document you have written, include a copy of
-the License in the document and put the following copyright and
-license notices just after the title page:
-
address@hidden
address@hidden
- Copyright (C) @var{year} @var{your name}.
- Permission is granted to copy, distribute and/or modify this document
- under the terms of the GNU Free Documentation License, Version 1.3
- or any later version published by the Free Software Foundation;
- with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
- Texts. A copy of the license is included in the section entitled ``GNU
- Free Documentation License''.
address@hidden group
address@hidden smallexample
-
-If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
-replace the address@hidden''@: line with this:
-
address@hidden
address@hidden
- with the Invariant Sections being @var{list their titles}, with
- the Front-Cover Texts being @var{list}, and with the Back-Cover Texts
- being @var{list}.
address@hidden group
address@hidden smallexample
-
-If you have Invariant Sections without Cover Texts, or some other
-combination of the three, merge those two alternatives to suit the
-situation.
-
-If your document contains nontrivial examples of program code, we
-recommend releasing these examples in parallel under your choice of
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-
address@hidden Local Variables:
address@hidden ispell-local-pdict: "ispell-dict"
address@hidden End:
diff --git a/shepherd.texi b/shepherd.texi
deleted file mode 100644
index 5dc5f9c..0000000
--- a/shepherd.texi
+++ /dev/null
@@ -1,1593 +0,0 @@
-\input texinfo @c -*- texinfo -*-
address@hidden shepherd.texi -- The documentation in Texinfo format.
address@hidden UTF-8
address@hidden shepherd.info
address@hidden The GNU Shepherd Manual
-
address@hidden version.texi
address@hidden OLD-YEARS 2002, 2003
address@hidden NEW-YEARS 2013, 2016
-
address@hidden
-Copyright @copyright{} @value{OLD-YEARS} Wolfgang J@"address@hidden
-Copyright @copyright{} @value{NEW-YEARS} Ludovic Courtès
-
-Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.3 or
-any later version published by the Free Software Foundation; with no
-Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
-copy of the license is included in the section entitled ``GNU Free
-Documentation License''.
address@hidden copying
-
address@hidden System software
address@hidden
-* shepherd: (shepherd). The Shepherd service manager.
-* herd: (shepherd)Invoking herd
- Controlling the Shepherd service manager.
-* reboot: (shepherd)Invoking reboot
- Rebooting a Shepherd-controlled system.
-* halt: (shepherd)Invoking halt
- Turning off a Shepherd-controlled system.
address@hidden direntry
-
address@hidden
address@hidden The GNU Shepherd Manual
address@hidden For use with the GNU Shepherd @value{VERSION}
address@hidden Last updated @value{UPDATED}
-
address@hidden Wolfgang J@"ahrling
address@hidden Ludovic Courtès
-
address@hidden
address@hidden titlepage
-
address@hidden
-
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden
address@hidden Top
address@hidden The GNU Shepherd Manual
-
-This manual documents the address@hidden version @value{VERSION}, a
-service manager for the GNU system.
-
address@hidden
-* Introduction:: Introduction to the Shepherd service manager.
-* Jump Start:: How to do simple things with the Shepherd.
-* herd and shepherd:: User interface to service management.
-* Services:: Details on services.
-* Runlevels:: Details on runlevels.
-* Misc Facilities:: Generally useful things provided by the Shepherd.
-* Internals:: Hacking shepherd.
-
-* GNU Free Documentation License:: The license of this manual.
-* Concept Index::
-* Procedure and Macro Index::
-* Variable Index::
-* Type Index::
address@hidden menu
address@hidden ifnottex
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Introduction
address@hidden Introduction
-
address@hidden service manager
-This manual documents the address@hidden Shepherd, or address@hidden
-for short. The Shepherd looks after system services, typically @dfn{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 @dfn{init system} of the GNU operating system---it is the
-first user process that gets started, typically with PID 1, and runs
-as @code{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
-(@pxref{Jump Start}). In chapter two we will describe the
address@hidden and @command{shepherd} programs, and their relationship, in
-more detail (@ref{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.
-
address@hidden dmd
-The Shepherd was formerly known as ``dmd'', which stands for @dfn{Daemon
-Managing Daemons} (or @dfn{Daemons-Managing Daemon}?).
-
address@hidden Guile
address@hidden Scheme
address@hidden GOOPS
-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.
address@hidden,,, guile, 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.
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Jump Start
address@hidden Jump Start
-
address@hidden prefix
-This chapter gives a short overview of the Shepherd. It is enough if you just
-need the basic features of it. As it is not assumed that readers are
-familiar with all the involved issues, a very experienced user might
-be annoyed by the often very detailed descriptions in this
-introduction. Those users are encouraged to just skip to the
-reference section.
-
-Note that all the full file names in the following text are based on
-the assumption that you have installed the Shepherd with an empty prefix. If
-your the Shepherd installation for example resides in @code{/usr/local}
-instead, add this directory name in front of the absolute file names
-mentioned below.
-
address@hidden Configuration file
-When @command{shepherd} gets started, it reads and evaluates a
-configuration file. When it is started with superuser priviledges, it
-tries to use @code{/etc/shepherd.scm}. When started as normal user, it
-looks for a file called @code{$XDG_CONFIG_HOME/shepherd/init.scm}. If
-the @code{XDG_CONFIG_HOME} environment variable is not defined,
address@hidden/.config/shepherd/init.scm} is used instead. With the option
address@hidden (or, for short, @code{-c}), you can specify where to
-look instead. So if you want to start @command{shepherd} with an
-alternative file, use one of the following commands:
-
address@hidden
-shepherd --config=/etc/shepherd.scm.old
-shepherd -c /etc/shepherd.scm.old
address@hidden example
-
address@hidden Starting a service
-As the final ``d'' suggests, @command{shepherd} is just
-a daemon that (usually) runs in the
-background, so you will not interact with it directly. After it is
-started, @command{shepherd} will listen on a socket special file, usually
address@hidden/var/run/shepherd/socket}, for further commands. You use the tool
address@hidden to send these commands to @command{shepherd}. Usage of herd is
simple and
-straightforward: To start a service called @code{apache}, you use:
-
address@hidden
-herd start apache
address@hidden example
-
address@hidden Status (of services)
address@hidden Service status
-When you do this, all its dependencies will get resolved. For
-example, a webserver is quite likely to depend on working networking,
-thus it will depend on a service called @code{networking}. So if you
-want to start @code{apache}, and @code{networking} is not yet running, it
-will automatically be started as well. The current status of all the
-services defined in the configuration file can be queried like this:
-
address@hidden
-herd status
address@hidden example
-
address@hidden
-Or, to get additional details about each service, run:
-
address@hidden
-herd detailed-status
address@hidden example
-
address@hidden
-In this example, this would show the @code{networking} and @code{apache}
-services as started. If you just want to know the status of the
address@hidden service, run:
-
address@hidden
-herd status apache
address@hidden example
-
address@hidden Stopping a service
-You can stop
-a service and all the services that depend on it will be stopped.
-Using the example above, if you stop @code{networking}, the service
address@hidden will be stopped as well---which makes perfect sense,
-as it cannot work without the network being up. To actually stop a
-service, you use the following, probably not very surprising, command:
-
address@hidden
-herd stop networking
address@hidden example
-
-There are two more actions you can perform on every service: The
-actions @code{enable} and @code{disable} are used to prevent and allow
-starting of the particular service. If a service is intended to be
-restarted whenever it terminates (how this can be done will not be
-covered in this introduction), but it is respawning too often in a
-short period of time (by default 5 times in 5 seconds), it will
-automatically be disabled. After you have fixed the problem that
-caused it from being respawned too fast, you can start it again with
-the commands:
-
address@hidden
-herd enable foo
-herd start foo
address@hidden example
-
address@hidden virtual services
address@hidden fallback services
-But there is far more you can do than just that. Services can not
-only simply depend on other services, they can also depend on
address@hidden services. A virtual service is a service that is
-provided by one or more service additionally. For instance, a service
-called @code{exim} might provide the virtual service
address@hidden That could as well be provided by a service
-called @code{smail}, as both are mailer-daemons. If a service needs
-any mailer-daemon, no matter which one, it can just depend on
address@hidden, and one of those who provide it gets started (if
-none is running yet) when resolving dependencies. The nice thing is
-that, if trying to start one of them fails, @command{shepherd} will go on and
try to
-start the next one, so you can also use virtual services for
-specifying @emph{fallbacks}.
-
-Additionally to all that, you can perform service-specific actions.
-Coming back to our original example, @code{apache} is able to
-reload its modules, therefore the action @code{reload-modules} might
-be available:
-
address@hidden
-herd reload-modules apache
address@hidden example
-
-The service-specific actions can only be used when the service is
-started, i.e. the only thing you can do to a stopped service is
-starting it. An exception exists, see below. (If you may at some
-point find this too restrictive because you want to use variants of
-the same service which are started in different ways, consider using
-different services for those variants instead, which all provide the
-same virtual service and thus conflict with each other, if this is
-desired. That's one of the reasons why virtual services exist, after
-all.)
-
-There are two actions which are special, because even if services
-can implement them on their own, a default implementation is provided
-by @command{shepherd} (another reason why they are special is that the default
-implementations can be called even when the service is not running;
-this inconsistency is just to make it more intuitive to get
-information about the status of a service, see below).
-
-These actions are @code{restart} and @code{status}. The default
-implementation of @code{restart} calls @code{stop} and @code{start} on
-the affected service in order, the @code{status} action displays some
-general information about the service, like what it provides, what it
-depends on and with which other services it conflicts (because they
-provide a virtual service that is also provided by that particular
-service).
-
-Another special action is @code{list-actions}, which displays a list
-of the additional actions a service provides; obviously, it can also
-be called when the service is not running. Services cannot provide
-their own implementation of @code{list-actions}.
-
-A special service is @code{root}, which is used for controlling the
-Shepherd itself. You can also reference to this service as
address@hidden It implements various actions. For example, the
address@hidden action displays which services are started and which ones
-are stopped, whereas @code{detailed-status} has the effect of applying
-the default implementation of @code{status} to all services one after
-another. The @code{load} action is unusual insofar as it shows a
-feature that is actually available to all services, but which we have
-not seen yet: It takes an additional argument. You can use @code{load}
-to load arbitrary code into the Shepherd at runtime, like this:
-
address@hidden
-herd load shepherd ~/additional-services.scm
address@hidden example
-
-This is enough now about the @command{herd} and @command{shepherd} programs, we
-will now take a look at how to configure the Shepherd. In the configuration
-file, we need mainly the definition of services. We can also do
-various other things there, like starting a few services already.
-
-FIXME: Finish. For now, look at the @code{examples/} subdirectory.
-
address@hidden
-...
address@hidden example
-
-Ok, to summarize:
-
address@hidden @bullet
address@hidden
address@hidden is a daemon, @command{herd} the program that controls it.
address@hidden
-You can start, stop, restart, enable and disable every service, as
-well as display its status.
address@hidden
-You can perform additional service-specific actions, which you can
-also list.
address@hidden
-Actions can have arguments.
address@hidden
-You can display the status of a service, even if the service does not
-provide a specific implementation for this action. The same is true
-for restarting.
address@hidden
-The @code{root}/@code{shepherd} service is used to control
address@hidden itself.
address@hidden itemize
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden herd and shepherd
address@hidden @command{herd} and @command{shepherd}
-
address@hidden herd
address@hidden shepherd
address@hidden daemon
address@hidden daemon controller
address@hidden relative file names
address@hidden herding, of daemons
-The daemon that runs in the background and is responsible for
-controlling the services is @command{shepherd}, while the user interface
-tool is called @command{herd}: it's the command that allows you to
-actually @emph{herd} your address@hidden
address@hidden deco, daemon controller
-In the past, when the
address@hidden was known as address@hidden, the @command{herd} command
-was called @code{deco}, for @dfn{DaEmon COntroller}.}. To perform an
-action, like stopping a service or calling an action of a service, you
-use the herd program. It will communicate with shepherd over a Unix
-Domain Socket.
-
-Thus, you start @command{shepherd} once, and then always use herd whenever you
want
-to do something service-related. Since herd passes its current
-working directory to @command{shepherd}, you can pass relative file names
without
-trouble. Both @command{shepherd} and herd understand the standard arguments
address@hidden, @code{--version} and @code{--usage}.
-
-
address@hidden
-* Invoking shepherd:: How to start the service damon.
-* Invoking herd:: Controlling daemons.
-* Invoking reboot:: Rebooting a shepherd-controlled system.
-* Invoking halt:: Turning off a shepherd-controlled system.
address@hidden menu
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Invoking shepherd
address@hidden Invoking @command{shepherd}
-
address@hidden @command{shepherd} Invocation
address@hidden invoking @command{shepherd}
-The @code{shepherd} program has the following synopsis:
-
address@hidden
-shepherd address@hidden@dots{}]
address@hidden example
-
-It accepts the following options:
-
address@hidden @samp
address@hidden -c @var{file}
address@hidden address@hidden
-Read and evaluate @var{file} as the configuration script on startup.
-
address@hidden is evaluated in the context of a fresh module where bindings
-from the @code{(shepherd service)} module and Guile's @code{(oop goops)} are
-available, in addition to the default set of Guile bindings. In
-particular, this means that code in @var{file} may use
address@hidden, the @code{<service>} class, and related tools
-(@pxref{Services}).
-
address@hidden -I
address@hidden --insecure
address@hidden security
address@hidden insecure
-Do not check if the directory where the socket---our communication
-rendez-vous with @command{herd}---is located has permissions @code{700}.
-If this option is not specified, @command{shepherd} will abort if the
-permissions are not as expected.
-
address@hidden -l address@hidden
address@hidden address@hidden
address@hidden logging
address@hidden log file
-Log output into @var{file}, or if @var{file} is not given,
address@hidden/var/log/shepherd.log} when running as superuser,
address@hidden/shepherd/shepherd.log} otherwise.
-
address@hidden address@hidden
-When @command{shepherd} is ready to accept connections, write its PID to
@var{file} or
-to the standard output if @var{file} is omitted.
-
address@hidden -p address@hidden
address@hidden address@hidden
address@hidden FIXME-CRITICAL
-
address@hidden -s @var{file}
address@hidden address@hidden
address@hidden socket special file
-Receive further commands on the socket special file @var{file}. If
-this option is not specified, @address@hidden/run/shepherd/socket} is
-taken.
-
-If @code{-} is specified as file name, commands will be read from
-standard input, one per line, as would be passed on a @command{herd}
-command line (@pxref{Invoking herd}).
-
address@hidden --quiet
-Synonym for @code{--silent}.
-
address@hidden table
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Invoking herd
address@hidden Invoking herd
-
address@hidden herd
-The @command{herd} command is a generic client program to control a
-running instance of @command{shepherd} (@pxref{Invoking shepherd}). It has the
-following synopsis:
-
address@hidden
-herd address@hidden@dots{}] @var{action} address@hidden address@hidden@dots{}]]
address@hidden example
-
-It causes the @var{action} of the @var{service} to be invoked. When
address@hidden is omitted and @var{action} is @code{status} or
address@hidden, the @code{root} service is address@hidden
-shorthand does not work for other actions such as @code{stop}, because
-inadvertently typing @code{herd stop} would stop all the services, which
-could be pretty annoying.} (@pxref{The root and unknown services}, for
-more information on the @code{root} service.)
-
-For each action, you should pass the appropriate @var{arg}s. Actions
-that are available for every service are @code{start}, @code{stop},
address@hidden, @code{status}, @code{enable}, @code{disable}, and
address@hidden
-
-If you pass a file name as an @var{arg}, it will be passed as-is to
-the Shepherd, thus if it is not an absolute name, it is local to the current
-working directory of @command{shepherd}, not to herd.
-
-The @code{herd} command understands the following option:
-
address@hidden @samp
-
address@hidden -s @var{file}
address@hidden address@hidden
-Send commands to the socket special file @var{file}. If this option is
-not specified, @address@hidden/run/shepherd/socket} is taken.
-
address@hidden table
-
-The @code{herd} command returns zero on success, and a non-zero exit
-code on failure. In particular, it returns a non-zero exit code when
address@hidden or @var{service} does not exist and when the given action
-failed.
-
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Invoking reboot
address@hidden Invoking reboot
-
address@hidden herd
-The @command{reboot} command is a convenience client program to instruct
-the Shepherd (when used as an init system) to stop all running services and
-reboot the system. It has the following synopsis:
-
address@hidden
-reboot address@hidden@dots{}]
address@hidden example
-
-It is equivalent to running @command{herd stop shepherd}. The
address@hidden command understands the following option:
-
address@hidden @samp
-
address@hidden -s @var{file}
address@hidden address@hidden
-Send commands to the socket special file @var{file}. If this option is
-not specified, @address@hidden/run/shepherd/socket} is taken.
-
address@hidden table
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Invoking halt
address@hidden Invoking halt
-
address@hidden herd
-The @command{halt} command is a convenience client program to instruct
-the Shepherd (when used as an init system) to stop all running services and
turn
-off the system. It has the following synopsis:
-
address@hidden
-halt address@hidden@dots{}]
address@hidden example
-
-It is equivalent to running @command{herd power-off shepherd}. As
-usual, the @code{halt} command understands the following option:
-
address@hidden @samp
-
address@hidden -s @var{file}
address@hidden address@hidden
-Send commands to the socket special file @var{file}. If this option is
-not specified, @address@hidden/run/shepherd/socket} is taken.
-
address@hidden table
-
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Services
address@hidden Services
-
address@hidden service
address@hidden <service>
-The @dfn{service} is obviously a very important concept of the Shepherd. On
the
-Guile level, a service is represented as an instance of
address@hidden<service>}, a GOOPS class (@pxref{GOOPS,,, guile, GNU Guile
-Reference Manual}). When creating an instance of it, you can specify
-the initial values of its slots, and you actually must do this for some
-of the slots.
-
-The @code{<service>} class and its associated procedures and methods are
-defined in the @code{(shepherd service)} module.
-
address@hidden
-* Slots of services:: What a <service> object consists of.
-* Methods of services:: What you can do with a <service> object.
-* Service Convenience:: How to conveniently work with services.
-* Service De- and Constructors:: Commonly used ways of starting and
- stopping services.
-* Service Examples:: Examples that show how services are used.
-* The root and unknown services:: Special services in the Shepherd.
address@hidden menu
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Slots of services
address@hidden Slots of services
-
address@hidden <service>, slots of
address@hidden slots of <service>
-A service has the following slots, all of which can be initialized
-with a keyword (i.e. @code{#:provides}, used when creating the object)
-of the same name, except where stated otherwise. You should not
-access them directly with @code{slot-ref} or @code{slot-set!}
-usually, use the methods of the service class @ref{Methods of
-services} instead.
-
address@hidden @bullet
address@hidden
address@hidden provides (slot of <service>)
address@hidden canonical names of services
address@hidden is a list of symbols that are provided by the service.
-A symbol can only be provided by one service running at a time,
-i.e. if two services provide the same symbol, only one of them can
-run, starting the other one will fail. Therefore, these symbols are
-mainly used to denote conflicting services. The first symbol in the
-list is the canonical name for the service, thus it must be unique.
-This slot has no default value and must therefore be initialized.
-
address@hidden
address@hidden requires (slot of <service>)
address@hidden is, like @code{provides}, a list of symbols that
-specify services. In this case, they name what this service depends
-on, i.e. before the service can be started, services that provide
-those symbols must be started. If a required symbol is provided by
-several services, one will be started. By default, this slot
-contains the empty list.
-
address@hidden
address@hidden running (slot of <service>)
address@hidden Hook for individual services
address@hidden is a hook that can be used by each service in its own
-way. The default value is @code{#f}, which indicates that the service
-is not running. When an attempt is made to start the service, it will
-be set to the return value of the procedure in the @code{start} slot.
-It will also be passed as an argument to the procedure in the
address@hidden slot. This slot can not be initialized with a keyword.
-
address@hidden
address@hidden respawn? (slot of <service>)
address@hidden Respawning services
address@hidden specifies whether the service should be respawned by
-the Shepherd. If this slot has the value @code{#t}, then assume the
address@hidden slot specifies a child process PID and restart the
-service if that process terminates. Otherwise this slot is @code{#f},
-which is the default. See also the @code{last-respawns} slot.
-
address@hidden
address@hidden start (slot of <service>)
address@hidden Starting a service
address@hidden Service constructor
address@hidden contains the ``constructor'' for the service, which will
-be called to start the service. (Therefore, it is not a constructor
-in the sense that it initializes the slots of a @code{<service>}
-object.) This must be a procedure that accepts any amount of
-arguments, which will be the additional arguments supplied by the
-user. If the starting attempt failed, it must return @code{#f}. The
-value will be stored in the @code{running} slot. The default value is
-a procedure that returns @code{#t} and performs no further actions,
-therefore it is desirable to specify a different one usually.
-
address@hidden
address@hidden stop (slot of <service>)
address@hidden Stoping a service
address@hidden Service destructor
address@hidden is, similar to @code{start}, a slot containing a
-procedure. But in this case, it gets the current value of the
address@hidden slot as first argument and the user-supplied arguments
-as further arguments; it gets called to stop the service. Its return
-value will again be stored in the @code{running} slot, so that it
-should return @code{#f} if it is now possible again to start the
-service at a later point. The default value is a procedure that
-returns @code{#f} and performs no further actions.
-
address@hidden
address@hidden actions (slot of <service>)
address@hidden Actions of services
address@hidden Service actions
address@hidden specifies the additional actions that can be performed
-on a service when it is running. A typical example for this is the
address@hidden action. The macro @code{make-actions} @ref{Service
-Convenience} is provided to abstract the actual data representation
-format for this slot. (It actually is a hash currently.)
-
address@hidden
address@hidden enabled? (slot of <service>)
address@hidden cannot be initialized with a keyword, and contains
address@hidden by default. When the value becomes @code{#f} at some point,
-this will prevent the service from getting started. A service can be
-enabled and disabled with the methods @code{enable} and
address@hidden, respectively @ref{Methods of services}.
-
address@hidden
address@hidden last-respawns (slot of <service>)
address@hidden cannot be initialized with a keyword and is only
-ever used when the @code{respawn?} slot contains @code{#t}; it is a
-circular list with @code{(car respawn-limit)} elements, where each
-element contains the time when it was restarted, initially all 0,
-later a time in seconds since the Epoch. The first element is the one
-that contains the oldest one, the last one the newest.
-
address@hidden
address@hidden stop-delay? (slot of <service>)
address@hidden being false causes the @code{stop} slot to be
-unused; instead, stopping the service will just cause the
address@hidden slot be set to @code{#t}.
-
address@hidden
address@hidden waiting-for-termination? (slot of <service>)
address@hidden cannot be initialized with a keyword
-and should not be used by others, it is only used internally for
-respawnable services when the @code{stop-delay?} slot contains a true
-value. @code{waiting-for-termination?} contains @code{#t} if the
-service is still running, but the user requested that it be stopped,
-in which case if the service terminates the next time, the respawn
-handler will not start it again.
-
-otherwise @code{#f}.
-
address@hidden itemize
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Methods of services
address@hidden Methods of services
-
address@hidden {method} start (obj <service>)
-Start the service @var{obj}, including all the services it depends on.
-It tries quite hard to do this: When a service that provides a
-required symbol can not be started, it will look for another service
-that also provides this symbol, until starting one such service
-succeeds. There is some room for theoretical improvement here, of
-course, but in pratice the current strategy already works very well.
-This method returns the new value of the @code{running} slot
address@hidden of services}, which is @code{#f} if the service could not
-be started.
address@hidden deffn
-
address@hidden {method} stop (obj <service>)
-This will stop the service @var{obj}, trying to stop services that
-depend in it first, so they can be shutdown cleanly. If this will
-fail, it will continue anyway. Stopping of services should usually
-succeed, though. Otherwise, the behaviour is very similar to the
address@hidden method. The return value is also the new @code{running}
-value, thus @code{#f} if the service was stopped.
address@hidden deffn
-
address@hidden {method} action (obj <service>) the-action . args
-Calls the action @var{the-action} (a symbol) of the service @var{obj},
-with the specified @var{args}, which have a meaning depending on the
-particular action.
address@hidden deffn
-
address@hidden {method} conflicts-with (obj <service>)
-Returns a list of the canonical names of services that conflict with
-the service @var{obj}.
address@hidden deffn
-
address@hidden {method} canonical-name (obj <service>)
-Returns the canonical name of @var{obj}, which is the first element of
-the @code{provides} list.
address@hidden deffn
-
address@hidden {method} provided-by (obj <service>)
-Returns which symbols are provided by @var{obj}.
address@hidden deffn
-
address@hidden {method} required-by (obj <service>)
-Returns which symbols are required by @var{obj}.
address@hidden deffn
-
address@hidden {method} running? (obj <service>)
-Returns whether the service @var{obj} is running.
address@hidden deffn
-
address@hidden {method} respawn? (obj <service>)
-Returns whether the service @var{obj} should be respawned if it
-terminates.
address@hidden deffn
-
address@hidden {method} default-display-status (obj <service>)
-Display status information about @var{obj}. This method is called
-when the user performs the action @code{status} on @var{obj}, but
-there is no specific implementation given for it. It is also called
-when @code{detailed-status} is applied on the @code{root} service.
address@hidden deffn
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Service Convenience
address@hidden Service Convenience
-
-In addition to the facilities listed below, there are also some
-procedures that provide commonly needed constructors and destructors
-for services @ref{Service De- and Constructors}.
-
address@hidden {procedure} register-services . services
-Register all @var{services}, so that they can be taken into account
-when trying to resolve dependencies.
address@hidden deffn
-
address@hidden {procedure} lookup-services name
-Return a list of all registered services which provide the symbol
address@hidden
address@hidden deffn
-
address@hidden {macro} make-actions (name proc) ...
-This macro is used to create a value for the @code{actions} slot of a
-service object @ref{Slots of services}. Each @var{name} is a symbol
-and each @var{proc} the corresponding procedure that will be called to
-perform the action. A @var{proc} has one argument, which will be the
-current value of the @code{running} slot of the service.
address@hidden deffn
-
address@hidden {method} start (obj <symbol>)
-Start a registered service providing @var{obj}.
address@hidden deffn
-
address@hidden {method} stop (obj <symbol>)
-Stop a registered service providing @var{obj}.
address@hidden deffn
-
address@hidden {method} action (obj <symbol>) the-action . args
-The same as the @code{action} method of class @code{<service>}, but
-uses a service that provides @var{obj} and is running.
address@hidden deffn
-
address@hidden {procedure} for-each-service proc
-Call @var{proc}, a procedure taking one argument, once for each
-registered service.
address@hidden deffn
-
address@hidden {procedure} find-running services
-Check if any of @var{services} is running. If this is the case,
-return its canonical name. If not, return @code{#f}. Only the first
-one will be returned; this is because this is mainly intended to be
-applied on the return value of @code{lookup-services}.
address@hidden deffn
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Service De- and Constructors
address@hidden Service De- and Constructors
-
address@hidden generating constructors
address@hidden generating destructors
address@hidden constructors, generation of
address@hidden destructors, generation of
-All of the procedures listed below return procedures generated from
-the supplied arguments. These procedures take one argument in the
-case of destructors and no arguments in the case of constructors.
-
address@hidden {procedure} make-system-constructor @address@hidden
-The returned procedure will execute @var{command} in a shell and
-return @code{#t} if execution was successful, otherwise @code{#f}.
-For convenience, it takes multiple arguments which will be
-concatenated first.
address@hidden deffn
-
address@hidden {procedure} make-system-destructor @address@hidden
-Similar to @code{make-system-constructor}, but returns @code{#f} if
-execution of the @var{command} was successful, @code{#t} if not.
address@hidden deffn
-
address@hidden {procedure} make-forkexec-constructor @var{command} @
- [#:user #f] @
- [#:group #f] @
- [#:pid-file #f] @
- [#:directory (default-service-directory)] @
- [#:environment-variables (default-environment-variables)]
-Return a procedure that forks a child process, closes all file
-descriptors except the standard output and standard error descriptors, sets
-the current directory to @var{directory}, changes the environment to
address@hidden (using the @code{environ} procedure), sets the
-current user to @var{user} and the current group to @var{group} unless they
-are @code{#f}, and executes @var{command} (a list of strings.) The result of
-the procedure will be the PID of the child process.
-
-When @var{pid-file} is true, it must be the name of a PID file
-associated with the process being launched; the return value is the PID
-read from that file, once that file has been created.
address@hidden deffn
-
address@hidden {procedure} make-kill-destructor address@hidden
-Returns a procedure that sends @var{signal} to the pid which it takes
-as argument. This @emph{does} work together with respawning services,
-because in that case the @code{stop} method of the @code{<service>}
-class sets the @code{running} slot to @code{#f} before actually
-calling the destructor; if it would not do that, killing the process
-in the destructor would immediately respawn the service.
address@hidden deffn
-
-The @code{make-forkexec-constructor} procedure builds upon the following
-procedures.
-
address@hidden {procedure} exec-command @var{command} @
- [#:user #f] @
- [#:group #f] @
- [#:directory (default-service-directory)] @
- [#:environment-variables (default-environment-variables)]
address@hidden {procedure} fork+exec-command @var{command} @
- [#:user #f] @
- [#:group #f] @
- [#:directory (default-service-directory)] @
- [#:environment-variables (default-environment-variables)]
-Run @var{command} as the current process from @var{directory}, and with
address@hidden (a list of strings like @code{"PATH=/bin"}.)
-File descriptors 1 and 2 are kept as is, whereas file descriptor 0
-(standard input) points to @file{/dev/null}; all other file descriptors
-are closed prior to yielding control to @var{command}.
-
-By default, @var{command} is run as the current user. If the
address@hidden keyword argument is present and not false, change to
address@hidden immediately before invoking @var{command}. @var{user} may
-be a string, indicating a user name, or a number, indicating a user
-ID. Likewise, @var{command} will be run under the current group,
-unless the @var{group} keyword argument is present and not false.
-
address@hidden does the same as @code{exec-command}, but in
-a separate process whose PID it returns.
address@hidden deffn
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Service Examples
address@hidden Service Examples
-
-FIXME: This needs a lot of work.
-
-You can create a service and then register it this way:
-
address@hidden
-(define apache (make <service>
- #:provides '(apache)
- #:start (...)
- #:stop (...)))
-(register-services apache)
address@hidden lisp
-
-However, as you usually won't need a variable for the service, you can
-pass it directly to @code{register-services}. Here is an example that
-also specifies some more initial values for the slots:
-
address@hidden
-(register-services
- (make <service>
- #:provides '(apache-2.0 apache httpd)
- #:requires '()
- #:start (...)
- #:stop (...)
- #:actions (make-actions
- (reload-modules (...))
- (restart (...)))))
address@hidden lisp
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden The root and unknown services
address@hidden The @code{root} and @code{unknown} services
-
address@hidden root service
address@hidden special services
-The service @code{root} is special, because it is used to control the
-Shepherd itself. It has an alias @code{shepherd}. It provides the
-following actions (in addition to @code{enable}, @code{disable} and
address@hidden which do not make sense here).
-
address@hidden @code
address@hidden status
-Displays which services are started and which ones are not.
-
address@hidden detailed-status
-Displays detailed information about every registered service.
-
address@hidden load @var{file}
-Evaluate the Scheme code in @var{file} in a fresh module that uses the
address@hidden(oop goops)} and @code{(shepherd services)} modules---as with the
address@hidden option of @command{shepherd} (@pxref{Invoking shepherd}).
-
address@hidden unload @var{service-name}
-Attempt to remove the service identified by @var{service-name}.
address@hidden will first stop the service, if necessary, and then
-remove it from the list of registered services. Any services
-depending upon @var{service-name} will be stopped as part of this
-process.
-
-If @var{service-name} simply does not exist, output a warning and do
-nothing. If it exists, but is provided by several services, output a
-warning and do nothing. This latter case might occur for instance with
-the fictional service @code{web-server}, which might be provided by both
address@hidden and @code{nginx}. If @var{service-name} is the special
-string and @code{all}, attempt to remove all services except for the Shepherd
-itself.
-
address@hidden reload @var{file-name}
-Unload all known optional services using unload's @code{all} option,
-then load @var{file-name} using @code{load} functionality. If
-file-name does not exist or @code{load} encounters an error, you may
-end up with no defined services. As these can be reloaded at a later
-stage this is not considered a problem. If the @code{unload} stage
-fails, @code{reload} will not attempt to load @var{file-name}.
-
address@hidden daemonize
-Fork and go into the background. This should be called before
-respawnable services are started, as otherwise we would not get the
address@hidden signals when they terminate.
-
address@hidden enable-persistency
-When terminating, safe the list of running services in a file.
address@hidden FIXME-CRITICAL: How can we specify which one?
-
address@hidden disable-persistency
-Don't safe the list of running services when terminating.
-
address@hidden table
-
address@hidden unknown service
address@hidden fallback service
-The @code{unknown} service must be defined by the user and if it
-exists, is used as a fallback whenever we try to invoke an unknown
-action of an existing service or use a service that does not exist.
-This is useful only in few cases, but enables you to do various sorts
-of unusual things.
-
address@hidden FIXME-CRITICAL: finish
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Runlevels
address@hidden Runlevels
-
-RUNLEVELS DO NOT WORK YET! Do not use them! Ignore this section!
-
address@hidden runlevel
address@hidden <runlevel>
-A @dfn{runlevel} makes it easier to start and stop groups of services,
-to bring the system into a certain state. An object of class
address@hidden<runlevel>} is an abstract runlevel, and has the following
-methods:
-
address@hidden {method} enter (rl <runlevel>) services
-This will be called when the runlevel should be entered.
address@hidden is the list of the currently running services.
address@hidden deffn
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Misc Facilities
address@hidden Misc Facilities
-
-This is a list of facilities which are available to code running
-inside of the Shepherd and is considered generally useful, but is not directly
-related to one of the other topic covered in this manual.
-
address@hidden
-* Errors:: Signalling, handling and ignoring errors.
-* Communication:: Input/Output in various ways.
-* Others:: Stuff that is useful, but is homeless.
address@hidden menu
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Errors
address@hidden Errors
-
address@hidden assertions
address@hidden {macro} assert expr
-If @var{expr} yields @code{#f}, display an appropriate error
-message and throw an @code{assertion-failed} exception.
address@hidden deffn
-
address@hidden {procedure} caught-error key args
-Tell the Shepherd that a @var{key} error with @var{args} has occured. This is
-the simplest way to cause caught error result in uniformly formated
-warning messages. The current implementation is not very good,
-though.
address@hidden deffn
-
address@hidden {procedure} call/cc proc
-An alias for @code{call-with-current-continuation}.
address@hidden deffn
-
address@hidden {procedure} call/ec proc
-A simplistic implementation of the nonstandard, but popular procedure
address@hidden, i.e. a @code{call/cc} for
-outgoing continuations only. Note that the variant included in the Shepherd is
-not aware of @code{dynamic-wind} at all and does not yet support
-returning multiple values.
address@hidden deffn
-
address@hidden system errors
address@hidden {macro} without-system-error address@hidden
-Evaluates the @var{expr}s, not going further if a system error occurs,
-but also doing nothing about it.
address@hidden deffn
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Communication
address@hidden Communication
-
-The @code{(shepherd comm)} module provides primitives that allow clients such
-as @command{herd} to connect to @command{shepherd} and send it commands to
-control or change its behavior (@pxref{Slots of services, actions of
-services}).
-
address@hidden <shepherd-command>
-Currently, clients may only send @dfn{commands}, represented by the
address@hidden<shepherd-command>} type. Each command specifies a service it
-applies to, an action name, a list of strings to be used as arguments,
-and a working directory. Commands are instantiated with
address@hidden:
-
address@hidden {procedure} shepherd-command @var{action} @var{service} @
- [#:@var{arguments} '()] [#:@var{directory} (getcwd)]
-Return a new command (a @code{<shepherd-command>}) object for
address@hidden on @var{service}.
address@hidden deffn
-
address@hidden
-Commands may then be written to or read from a communication channel
-with the following procedures:
-
address@hidden {procedure} write-command @var{command} @var{port}
-Write @var{command} to @var{port}.
address@hidden deffn
-
address@hidden {procedure} read-command @var{port}
-Receive a command from @var{port} and return it.
address@hidden deffn
-
-In practice, communication with @command{shepherd} takes place over a
-Unix-domain socket, as discussed earlier (@pxref{Invoking shepherd}).
-Clients may open a connection with the procedure below.
-
address@hidden {procedure} open-connection address@hidden
-Open a connection to the daemon, using the Unix-domain socket at
address@hidden, and return the socket.
-
-When @var{file} is omitted, the default socket is used.
address@hidden deffn
-
address@hidden output
-The daemon writes output to be logged or passed to the
-currently-connected client using @code{local-output}:
-
address@hidden {procedure} local-output format-string . args
-This procedure should be used for all output operations in the Shepherd. It
-outputs the @var{args} according to the @var{format-string}, then
-inserts a newline. It writes to whatever is the main output target of
-the Shepherd, which might be multiple at the same time in future versions.
address@hidden deffn
-
address@hidden protocol, between @command{shepherd} and its clients
-Under the hood, @code{write-command} and @code{read-command} write/read
-commands as s-expressions (sexps). Each sexp is intelligible and
-specifies a protocol version. The idea is that users can write their
-own clients rather than having to invoke @command{herd}. For instance,
-when you type @command{herd status}, what is sent over the wire is the
-following sexp:
-
address@hidden
-(shepherd-command
- (version 0)
- (action status) (service root)
- (arguments ()) (directory "/data/src/dmd"))
address@hidden lisp
-
-The reply is also an sexp, along these lines:
-
address@hidden
-(reply (version 0)
- (result (((service @dots{}) @dots{})))
- (error #f) (messages ()))
address@hidden lisp
-
-This reply indicates that the @code{status} action was successful,
-because @code{error} is @code{#f}, and gives a list of sexps denoting
-the status of services as its @code{result}. The @code{messages} field
-is a possibly-empty list of strings meant to be displayed as is to the
-user.
-
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Others
address@hidden Others
-
address@hidden hashes
address@hidden {procedure} copy-hashq-table table new-size
-Create a hash-table with size @var{new-size}, and insert all values
-from @var{table} into it, using @code{eq?} when inserting. This
-procedure is mainly used internally, but is a generally useful
-utillity, so it can by used by everyone.
address@hidden deffn
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Internals
address@hidden Internals
-
-This chapter contains information about the design and the
-implementation details of the Shepherd for people who want to hack it.
-
-The address@hidden is developed by a group of people in connection
-with @uref{https://www.gnu.org/software/guix/, GuixSD}, GNU's advanced
-distribution, but it can be used on other distros as well. You're very
-much welcome to join us! You can report bugs to
address@hidden@@gnu.org} and send patches or suggestions to
address@hidden@@gnu.org}.
-
address@hidden
-* Coding standards:: How to properly hack the Shepherd.
-* Design decisions:: Why the Shepherd is what it is.
-* Service Internals:: How services actually work.
-* Runlevel evolution:: Learning from past mistakes.
address@hidden menu
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Coding standards
address@hidden Coding standards
-
-About formatting: Use common sense and GNU Emacs (which actually is
-the same, of course), and you almost can't get the formatting wrong.
-Formatting should be as in Guile and Guix, basically. @xref{Coding
-Style,,, guix, GNU Guix Reference Manual}, for more info.
-
address@hidden @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-
address@hidden Design decisions
address@hidden Design decisions
-
address@hidden Note
-This section was written by Wolfgang Jährling back in 2003 and documents
-the original design of what was then known as address@hidden The main
-ideas remain valid but some implementation details and goals have
-changed.
address@hidden quotation
-
-The general idea of a service manager that uses dependencies, similar
-to those of a Makefile, came from the developers of the GNU Hurd, but
-as few people are satisfied with System V Init, many other people had
-the same idea independently. Nevertheless, the Shepherd was written with the
-goal of becoming a replacement for System V Init on GNU/Hurd, which
-was one of the reasons for choosing the extension language of the GNU
-project, Guile, for implementation (another reason being that it makes
-it just so much easier).
-
-The runlevel concept (i.e. thinking in @emph{groups} of services) is
-sometimes useful, but often one also wants to operate on single
-services. System V Init makes this hard: While you can start and stop
-a service, @code{init} will not know about it, and use the runlevel
-configuration as its source of information, opening the door for
-inconsistencies (which fortunatly are not a practical problem
-usually). In the Shepherd, this was avoided by having a central entity that is
-responsible for starting and stopping the services, which therefore
-knows which services are actually started (if not completely
-inproperly used, but that is a requirement which is impossible to
-avoid anyway). While runlevels are not implemented yet, it is clear
-that they will sit on top of the service concept, i.e. runlevels will
-merely be an optional extension that the service concept does not rely
-on. This also makes changes in the runlevel design easier when it may
-become necessary.
-
-The consequence of having a daemon running that controls the services
-is that we need another program as user interface which communicates
-with the daemon. Fortunatly, this makes the commands necessary for
-controlling services pretty short and intuitive, and gives the
-additional bonus of adding some more flexibility. For example, it is
-easiely possible to grant password-protected control over certain
-services to unprivileged users, if desired.
-
-An essential aspect of the design of the Shepherd (which was already mentioned
-above) is that it should always know exactly what is happening,
-i.e. which services are started and stopped. The alternative would
-have been to not use a daemon, but to save the state on the file
-system, again opening the door for inconsistencies of all sorts.
-Also, we would have to use a seperate program for respawning a service
-(which just starts the services, waits until it terminates and then
-starts it again). Killing the program that does the respawning (but
-not the service that is supposed to be respawned) would cause horrible
-confusion. My understanding of ``The Right Thing'' is that this
-conceptionally limited strategy is exactly what we do not want.
-
-The way dependencies work in the Shepherd took a while to mature, as it was not
-easy to figure out what is appropriate. I decided to not make it too
-sophisticated by trying to guess what the user might want just to
-theoretically fulfill the request we are processing. If something
-goes wrong, it is usually better to tell the user about the problem
-and let her fix it, taking care to make finding solutions or
-workarounds for problems (like a misconfigured service) easy. This
-way, the user is in control of what happens and we can keep the
-implementation simple. To make a long story short, @emph{we don't try
-to be too clever}, which is usually a good idea in developing
-software.
-
-If you wonder why I was giving a ``misconfigured service'' as an
-example above, consider the following situation, which actually is a
-wonderful example for what was said in the previous paragraph: Service
-X depends on symbol S, which is provided by both A and B. A depends
-on AA, B depends on BB. AA and BB conflict with each other. The
-configuration of A contains an error, which will prevent it from
-starting; no service is running, but we want to start X now. In
-resolving its dependencies, we first try to start A, which will cause
-AA to be started. After this is done, the attempt of starting A
-fails, so we go on to B, but its dependency BB will fail to start
-because it conflicts with the running service AA. So we fail to
-provide S, thus X cannot be started. There are several possibilities
-to deal with this:
-
address@hidden @bullet
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-When starting A fails, terminate those services which have been
-started in order to fulfill its dependencies (directly and
-indirectly). In case AA was running already, we would not want to
-terminate it. Well, maybe we would, to avoid the conflict with BB.
-But even if we would find out somehow that we need to terminate AA to
-eventually start X, is the user aware of this and wants this to happen
-(assuming AA was running already)? Probably not, she very likely has
-assumed that starting A succeeds and thus terminating AA is not
-necessary. Remember, unrelated (running) services might depend in AA.
-Even if we ignore this issue, this strategy is not only complicated,
-but also far from being perfect: Let's assume starting A succeeds, but
-X also depends on a service Z, which requires BB. In that case, we
-would need to detect in the first place that we should not even try to
-start A, but directly satisfy X's dependency on S with B.
-
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-We could do it like stated above, but stop AA only if we know we won't
-need it anymore (for resolving further dependencies), and start it
-only when it does not conflict with anything that needs to get
-started. But should we stop it if it conflicts with something that
address@hidden get started? (We do not always know for sure what we
-will start, as starting a service might fail and we want to fall back
-to a service that also provides the particular required symbol in that
-case.) I think that either decision will be bad in one case or
-another, even if this solution is already horribly complicated.
-
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-When we are at it, we could just calculate a desired end-position, and
-try to get there by starting (and stopping!) services, recalculating
-what needs to be done whenever starting a service fails, also marking
-that particular service as unstartable, except if it fails to start
-because a dependency could not be resolved (or maybe even then?).
-This is even more complicated. Instead of implementing this and
-thereby producing code that (a) nobody understands, (b) certainly has
-a lot of bugs, (c) will be unmaintainable and (d) causes users to
-panic because they won't understand what will happen, I decided to do
-the following instead:
-
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-Just report the error, and let the user fix it (in this case, fix the
-configuration of A) or work around it (in this case, disable A so that
-we won't start AA but directly go on to starting B).
address@hidden itemize
-
-I hope you can agree that the latter solution after all is the best
-one, because we can be sure to not do something that the user does not
-want us to do. Software should not run amok. This explanation was
-very long, but I think it was necessary to justify why the Shepherd uses a very
-primitive algorithm to resolve dependencies, despite the fact that it
-could theoretically be a bit more clever in certain situations.
-
-One might argue that it is possible to ask the user if the planned
-actions are ok with her, and if the plan changes ask again, but
-especially given that services are supposed to usually work, I see few
-reasons to make the source code of the Shepherd more complicated than
-necessary. If you volunteer to write @emph{and} maintain a more
-clever strategy (and volunteer to explain it to everyone who wants to
-understand it), you are welcome to do so, of address@hidden
-
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-
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-
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-
address@hidden Runlevel evolution
address@hidden Runlevel evolution
-
address@hidden Note
-This section was written by Wolfgang Jährling back in 2003 and is kept
-mostly for historians to read.
address@hidden quotation
-
-This section describes how the runlevel concept evolved over time.
-This is basically a collection of mistakes, but is provided here for
-your information, and possibly for your amusement, but I'm not sure if
-all this weird dependency stuff is really that funny.
-
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-* Runlevel assumptions:: What runlevels should be like
-* Runlevels - part one:: The first attempts of making it work
-* Runlevels - part two:: It should work... somehow...
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-
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-
address@hidden Runlevel assumptions
address@hidden Runlevel assumptions
-
-A runlevel is a system state, i.e. it consists of the information
-about which services are supposed to be available and which not. This
-vague definition implies that several different runlevel styles can be
-implemented in a service manager.
-
-For example, you can do it like System V Init, specifying which
-services should be started when we enter a runlevel and which ones
-should be stopped when leaving it. But one could also specify for
-every service in which runlevels it should be running.
-
-In the Shepherd, we do not want to limit ourselfes to a single runlevel style.
-We allow for all possible strategies to be implemented, providing the
-most useful ones as defaults. We also want to make it possible to
-combine the different styles arbitrariely.
-
-Therefore, when entering a runlevel, we call a user-defined piece of
-code, passing it the list of currently active services and expecting
-as the result a list of service symbols which tell us which services
-we want to have running. This interface makes it very easy to
-implement runlevel styles, but makes it not-so-easy for the runlevel
-implementation itself, because we have to get from the current state
-into a desired state, which might be more or less vague (since it is
-not required to be a list of canonical names). Obviously service
-conflicts and already running services need to be taken into account
-when deciding which services should be used to provide the various
-symbols.
-
-Also, the runlevel implementation should be implemented completely on
-top of the service concept, i.e. the service part should not depend on
-the idea of runlevels or care about them at all. Otherwise
-understanding the service part (which is the most essential aspect of
-the Shepherd) would become harder than necessary.
-
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-
address@hidden Runlevels - part one
address@hidden Runlevels, part one
-
-I came up with the following method (here in Pseudo-Scheme), which is
-possibly slightly buggy, but should give you the idea:
-
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-;; Beginning with the canonical names in CURRENT-SERVICES, start and
-;; stop services until getting into a state where everything requested
-;; in TARGET-SERVICES (which does not only consist of canonical names)
-;; is provided, and the things they depends on, but no more.
-(define (switch-runlevel current-services target-services)
- (let ((target-services-backup target-services)
- (unstartable '()))
- (let retry ()
- (repeat-until-none-of-these-changes-annythig
- ;; Replace all of them with canonical names which provide them.
- (canonicalize-names! target-services unstartable current-services)
- ;; Add what we need additionally.
- (add-dependencies! target-services unstartable current-services))
- (remove-redundancy! target-services)
- (stop-all-unneeded target-services)
- (catch 'service-could-not-be-started
- (lambda ()
- ;; Iterate over the list, starting only those which
- ;; have all dependencies already resolved, so nothing
- ;; we don't want will be started. Repeat until done.
- (carefully-start target-services))
- (lambda (key service)
- (set! unstartable (cons service unstartable))
- (set! target-services backup-target-services)
- (set! current-services (compute-current-services))
- (retry))))))
address@hidden lisp
-
-This indeed looks like a nice way to get what we want. However, the
-details of this are not as easy as it looks like. When replacing
-virtual services with canonical names, we have to be very careful.
-Consider the following situation:
-
-The virtual service X is provided by both A and B, while Y is provided
-only by B. We want to start C (which depends on X) and D (which
-depends on Y). Obviously we should use B to fulfill the dependency
-of C and D on X and Y, respectively. But when we see that we need
-something that provides X, we are likely to do the wrong thing: Select
-A. Thus, we need to clean this up later. I wanted to do this as
-follows:
-
-While substituting virtual services with canonical names, we also safe
-which one we selected to fulfill what, like this:
-
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-((A . (X))
- (B . (Y)))
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-
-Later we look for conflicts, and as A and B conflict, we look which
-one can be removed (things they provide but are not required by anyone
-should be ignored, thus we need to create a list like the above). In
-this case, we can replace A with B as B also provides X (but A does
-not provide Y, thus the reverse is impossible). If both could be
-used, we probably should decide which one to use by looking at further
-conflicts, which gets pretty hairy. But, in this case, we are lucky
-and end up with this:
-
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-((B . (X Y)))
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-
-This way of finding out which service we should use in case of
-conflicts sounds pretty sane, but if you think it will work well, you
-have been fooled, because actually it breaks horribly in the following
-situation:
-
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address@hidden Service @tab Provides
address@hidden A @tab @code{W X Y -}
address@hidden B @tab @code{W X - Z}
address@hidden C @tab @code{- X Y Z}
address@hidden D @tab @code{W - - -}
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-
-If we need all of W, X, Y and Z, then obviously we need to take C and
-D. But if we have a list like this, we cannot fix it:
-
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-((A . (W X Y))
- (B . (Z)))
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-
-Thus, we cannot do it this way.
-
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-
address@hidden Runlevels - part two
address@hidden Runlevels, part two
-
-Let's look again at the table at the end of part two:
-
address@hidden @columnfractions .10 .30
address@hidden Service @tab Provides
address@hidden A @tab @code{W X Y -}
address@hidden B @tab @code{W X - Z}
address@hidden C @tab @code{- X Y Z}
address@hidden D @tab @code{W - - -}
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-
-If from this table it is so obvious for us what we should do, then it
-should also be possible to calculate it for a computer, given such a
-table as input. Ok, we have to take into account conflicts that are
-not visible in this table, but the general idea is usable. But how do
-we find which combination works? I found only one way yet: Kind of a
-brute force attack: Try combinations until we find one that works.
-
-This alone would be too slow. With 20 services we would have 2^20
-possible combinations, that is a bit more than a million. Fortunatly,
-we can optimize this. First I thought we could remove all services
-from the list that do not provide any symbol we need, but that is
-obviously a stupid idea, as we might need them for dependencies, in
-which case we need to take into account their conflicts. But the
-following method would work:
-
-Very often a symbol that is required will be a canonical name already,
-i.e. be provided only by a single service. Using our example above,
-let's suppose we also need the symbol V, which is provided only by D.
-The first step we do is to look which (required) symbols are provided
-only by a single service, as we will need this service for sure. In
-this case, we would need D. But by using it, we would also get the
-other symbols it provides, W in this case. This means that we don't
-need to bother looking at other services that provide W, as we cannot
-use them because they conflict with a service that we definitely need.
-In this case, we can remove A and B from the list this way. Note that
-we can remove them entirely, as all their conflicts become irrelevant
-to us now. In this simple case we would not even have to do much
-else, C is the only remaining service.
-
-After this first step, there remain the symbols that are provided by
-two or more services. In every combination we try, exactly one of
-them must be used (and somehow we should take into account which
-services are running already). This also reduces the amount of
-possible combinations a lot. So what remains after that are the
-services we might need for fulfilling dependencies. For them, we
-could try all combinations (2^n), making sure that we always try
-subsets before any of their supersets to avoid starting unneeded
-services. We should take into account which services are already
-running as well.
-
-The remaining question is, what to do if starting a service fails. A
-simple solution would be to recursively remove all services that
-depend on it directly or indirectly. That might cause undesired
-side-effects, if a service was running but it had to be stopped
-because one of the services that provides something it depends on gets
-exchanged for another service that provides the same symbol, but fails
-to start. The fact that we would have to stop the (first) service is
-a problem on its own, though.
-
-
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address@hidden GNU Free Documentation License
address@hidden GNU Free Documentation License
-
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-
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-
address@hidden Concept Index
address@hidden Concept Index
-
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-
address@hidden Procedure and Macro Index
address@hidden Procedure and Macro Index
-
address@hidden fn
-
address@hidden Variable Index
address@hidden Variable Index
-
address@hidden vr
-
address@hidden Type Index
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-
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-
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