Next: Complex Configurations, Previous: Интерфейс сервиса, Up: Создание служб [Contents][Index]
The (gnu services shepherd)
module provides a way to define services
managed by the GNU Shepherd, which is the initialization system—the
first process that is started when the system boots, also known as
PID 1 (see Introduction in The GNU Shepherd Manual).
Services in the Shepherd can depend on each other. For instance, the SSH daemon may need to be started after the syslog daemon has been started, which in turn can only happen once all the file systems have been mounted. The simple operating system defined earlier (see Использование системы конфигурации) results in a service graph like this:
You can actually generate such a graph for any operating system definition
using the guix system shepherd-graph
command
(see guix system shepherd-graph
).
The %shepherd-root-service
is a service object representing
PID 1, of type shepherd-root-service-type
; it can be extended by
passing it lists of <shepherd-service>
objects.
The data type representing a service managed by the Shepherd.
provision
This is a list of symbols denoting what the service provides.
These are the names that may be passed to herd start
,
herd status
, and similar commands (see Invoking herd in The GNU Shepherd Manual). See the
provides
slot in The GNU Shepherd Manual, for details.
features
(default: '()
)List of symbols denoting the Shepherd services this one depends on.
one-shot?
(default: #f
)Whether this service is one-shot. One-shot services stop immediately
after their start
action has completed. See Slots of services in The GNU Shepherd Manual, for more info.
respawn?
(default: #t
)Whether to restart the service when it stops, for instance when the underlying process dies.
start
stop
(default: #~(const #f)
)The start
and stop
fields refer to the Shepherd’s facilities
to start and stop processes (see Service De- and Constructors in The GNU Shepherd Manual). They are given as G-expressions that
get expanded in the Shepherd configuration file (see G-Expressions).
actions
(default: '()
) ¶This is a list of shepherd-action
objects (see below) defining
actions supported by the service, in addition to the standard
start
and stop
actions. Actions listed here become available
as herd
sub-commands:
herd action service [arguments…]
auto-start?
(default: #t
)Whether this service should be started automatically by the Shepherd. If it
is #f
the service has to be started manually with herd start
.
документация
A documentation string, as shown when running:
herd doc service-name
where service-name is one of the symbols in provision
(see Invoking herd in The GNU Shepherd Manual).
modules
(default: %default-modules
)This is the list of modules that must be in scope when start
and
stop
are evaluated.
The example below defines a Shepherd service that spawns syslogd
,
the system logger from the GNU Networking Utilities (see syslogd
in GNU Inetutils):
(let ((config (plain-file "syslogd.conf" "…"))) (shepherd-service (documentation "Run the syslog daemon (syslogd).") (provision '(syslogd)) (requirement '(user-processes)) (start #~(make-forkexec-constructor (list #$(file-append inetutils "/libexec/syslogd") "--rcfile" #$config) #:pid-file "/var/run/syslog.pid")) (stop #~(make-kill-destructor))))
Key elements in this example are the start
and stop
fields:
they are staged code snippets that use the
make-forkexec-constructor
procedure provided by the Shepherd and its
dual, make-kill-destructor
(see Service De- and Constructors in The GNU Shepherd Manual). The start
field will have
shepherd
spawn syslogd
with the given option; note that
we pass config
after --rcfile, which is a configuration file
declared above (contents of this file are omitted). Likewise, the
stop
field tells how this service is to be stopped; in this case, it
is stopped by making the kill
system call on its PID. Code staging
is achieved using G-expressions: #~
stages code, while #$
“escapes” back to host code (see G-Expressions).
This is the data type that defines additional actions implemented by a Shepherd service (see above).
name
Symbol naming the action.
документация
This is a documentation string for the action. It can be viewed by running:
herd doc service action action
процедура
This should be a gexp that evaluates to a procedure of at least one argument, which is the “running value” of the service (see Slots of services in The GNU Shepherd Manual).
The following example defines an action called say-hello
that kindly
greets the user:
(shepherd-action
(name 'say-hello)
(documentation "Say hi!")
(procedure #~(lambda (running . args)
(format #t "Hello, friend! arguments: ~s\n"
args)
#t)))
Assuming this action is added to the example
service, then you can
do:
# herd say-hello example Hello, friend! arguments: () # herd say-hello example a b c Hello, friend! arguments: ("a" "b" "c")
This, as you can see, is a fairly sophisticated way to say hello. See Service Convenience in The GNU Shepherd Manual, for more info on actions.
Return a configuration
action to display file, which should be
the name of the service’s configuration file.
It can be useful to equip services with that action. For example, the
service for the Tor anonymous router (see tor-service-type
) is defined roughly like this:
(let ((torrc (plain-file "torrc" …)))
(shepherd-service
(provision '(tor))
(requirement '(user-processes loopback syslogd))
(start #~(make-forkexec-constructor
(list #$(file-append tor "/bin/tor") "-f" #$torrc)
#:user "tor" #:group "tor"))
(stop #~(make-kill-destructor))
(actions (list (shepherd-configuration-action torrc)))
(documentation "Run the Tor anonymous network overlay.")))
Thanks to this action, administrators can inspect the configuration file
passed to tor
with this shell command:
cat $(herd configuration tor)
This can come in as a handy debugging tool!
The service type for the Shepherd “root service”—i.e., PID 1.
This is the service type that extensions target when they want to create
shepherd services (see Типы сервисов и сервисы, for an example).
Each extension must pass a list of <shepherd-service>
. Its value
must be a shepherd-configuration
, as described below.
Управление конфигурацией операционной системы.
port
(default: 22
)
Используемый пакет Hurd.
features
(default: '()
)
A list of <shepherd-service>
to start. You should probably use the
service extension mechanism instead (see Сервисы Shepherd).
Следующий пример порождает новую оболочку, установленную для разработки GNU Guile:
(operating-system
;; ...
(services (append (list openssh-service-type))
;; ...
%desktop-services)
;; ...
;; Use own Shepherd package.
(essential-services
(modify-services (operating-system-default-essential-services
this-operating-system)
(shepherd-root-service-type config => (shepherd-configuration
(inherit config)
(shepherd my-shepherd))))))
This service represents PID 1.
Next: Complex Configurations, Previous: Интерфейс сервиса, Up: Создание служб [Contents][Index]