(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 介绍 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 使用配置系统) results in a service graph like this:
You can actually generate such a graph for any operating system definition
guix system shepherd-graph command
guix system shepherd-graph).
%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
The data type representing a service managed by the Shepherd.
This is a list of symbols denoting what the service provides.
These are the names that may be passed to
herd status, and similar commands (see Invoking herd in The GNU Shepherd Manual). See the
provides slot in The GNU Shepherd Manual, for details.
List of symbols denoting the Shepherd services this one depends on.
Whether this service is one-shot. One-shot services stop immediately
start action has completed. See Slots of services in The GNU Shepherd Manual, for more info.
Whether to restart the service when it stops, for instance when the underlying process dies.
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-表达式).
This is a list of
shepherd-action objects (see below) defining
actions supported by the service, in addition to the standard
stop actions. Actions listed here become available
herd action service [arguments…]
Whether this service should be started automatically by the Shepherd. If it
#f the service has to be started manually with
A documentation string, as shown when running:
herd doc service-name
where service-name is one of the symbols in
(see Invoking herd in The GNU Shepherd Manual).
This is the list of modules that must be in scope when
stop are evaluated.
The example below defines a Shepherd service that spawns
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
they are staged code snippets that use the
make-forkexec-constructor procedure provided by the Shepherd and its
make-kill-destructor (see Service De- and Constructors in The GNU Shepherd Manual). The
start field will have
syslogd with the given option; note that
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-表达式).
This is the data type that defines additional actions implemented by a Shepherd service (see above).
Symbol naming the action.
This is a documentation string for the action. It can be viewed by running:
herd doc service action action
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
# 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.
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 服务类型和服务, for an example).
Each extension must pass a list of
<shepherd-service>. Its value
must be a
shepherd-configuration, as described below.
This data type represents the Shepherd’s configuration.
The Shepherd package to use.
A list of
<shepherd-service> to start. You should probably use the
service extension mechanism instead (see Shepherd服务).
The following example specifies the Shepherd package for the operating system:
(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.