smf– service management facility

Name

smf– service management facility

Description

The Solaris service management facility defines a programming model for providing persistently running applications called services. The facility also provides the infrastructure in which to run services. A service can represent a running application, the software state of a device, or a set of other services. Services are represented in the framework by service instance objects, which are children of service objects. Instance objects can inherit or override the configuration of the parent service object, which allows multiple service instances to share configuration information. All service and instance objects are contained in a scope that represents a collection of configuration information. The configuration of the local Solaris instance is called the “localhost” scope, and is the only currently supported scope.

Each service instance is named with a fault management resource identifier (FMRI) with the scheme “svc:”. For example, the syslogd(1M) daemon started at system startup is the default service instance named:

svc://localhost/system/system-log:default
svc:/system/system-log:default
system/system-log:default

In the above example, 'default' is the name of the instance and 'system/system-log' is the service name. Service names may comprise multiple components separated by slashes (/). All components, except the last, compose the category of the service. Site-specific services should be named with a category beginning with 'site'.

A service instance is either enabled or disabled. All services can be enabled or disabled with the svcadm(1M) command.

The list of managed service instances on a system can be displayed with the svcs(1) command.

Dependencies

Service instances may have dependencies on services or files. Those dependencies govern when the service is started and automatically stopped. When the dependencies of an enabled service are not satisfied, the service is kept in the offline state. When its dependencies are satisfied, the service is started. If the start is successful, the service is transitioned to the online state. Whether a dependency is satisfied is determined by its type:

require_all

Satisfied when all cited services are running (online or degraded), or when all indicated files are present.

require_any

Satisfied when one of the cited services is running (online or degraded), or when at least one of the indicated files is present.

optional_all

Satisfied if the cited services are running (online or degraded) or will not run without administrative action (disabled, maintenance, not present, or offline waiting for dependencies which will not start without administrative action).

exclude_all

Satisfied when all of the cited services are disabled, in the maintenance state, or when cited services or files are not present.

Once running (online or degraded), if a service cited by a require_all, require_any, or optional_all dependency is stopped or refreshed, the SMF considers why the service was stopped and the restart_on attribute of the dependency to decide whether to stop the service.

                   |  restart_on value
event              |  none  error restart refresh
-------------------+------------------------------
stop due to error  |  no    yes   yes     yes
non-error stop     |  no    no    yes     yes
refresh            |  no    no    no      yes

A service is considered to have stopped due to an error if the service has encountered a hardware error or a software error such as a core dump. For exclude_all dependencies, the service is stopped if the cited service is started and the restart_on attribute is not none.

The dependencies on a service can be listed with svcs(1) or svccfg(1M), and modified with svccfg(1M).

Restarters

Each service is managed by a restarter. The master restarter, svc.startd(1M) manages states for the entire set of service instances and their dependencies. The master restarter acts on behalf of its services and on delegated restarters that can provide specific execution environments for certain application classes. For instance, inetd(1M) is a delegated restarter that provides its service instances with an initial environment composed of a network connection as input and output file descriptors. Each instance delegated to inetd(1M) is in the online state. While the daemon of a particular instance might not be running, the instance is available to run.

As dependencies are satisfied when instances move to the online state, svc.startd(1M) invokes start methods of other instances or directs the delegated restarter to do so. These operations might overlap.

The current set of services and associated restarters can be examined using svcs(1). A description of the common configuration used by all restarters is given in smf_restarter(5).

Methods

Each service or service instance must define a set of methods that start, stop, and, optionally, refresh the service. See smf_method(5) for a more complete description of the method conventions for svc.startd(1M) and similar fork(2)-exec(2) restarters.

Administrative methods, such as for the capture of legacy configuration information into the repository, are discussed on the svccfg(1M) manual page.

The methods for a service can be listed and modified using the svccfg(1M) command.

States

Each service instance is always in a well-defined state based on its dependencies, the results of the execution of its methods, and its potential receipt of events from the contracts filesystem. The following states are defined:

UNINITIALIZED

This is the initial state for all service instances. Instances are moved to maintenance, offline, or a disabled state upon evaluation by svc.startd(1M) or the appropriate restarter.

OFFLINE

The instance is enabled, but not yet running or available to run. If restarter execution of the service start method or the equivalent method is successful, the instance moves to the online state. Failures might lead to a degraded or maintenance state. Administrative action can lead to the uninitialized state.

ONLINE

The instance is enabled and running or is available to run. The specific nature of the online state is application-model specific and is defined by the restarter responsible for the service instance. Online is the expected operating state for a properly configured service with all dependencies satisfied. Failures of the instance can lead to a degraded or maintenance state. Failures of services on which the instance depends can lead to offline or degraded states.

DEGRADED

The instance is enabled and running or available to run. The instance, however, is functioning at a limited capacity in comparison to normal operation. Failures of the instance can lead to the maintenance state. Failures of services on which the instance depends can lead to offline or degraded states. Restoration of capacity should result in a transition to the online state.

MAINTENANCE

The instance is enabled, but not able to run. Administrative action is required to restore the instance to offline and subsequent states. The maintenance state might be a temporarily reached state if an administrative operation is underway.

DISABLED

The instance is disabled. Enabling the service results in a transition to the offline state and eventually to the online state with all dependencies satisfied.

LEGACY-RUN

This state represents a legacy instance that is not managed by the service management facility. Instances in this state have been started at some point, but might or might not be running. Instances can only be observed using the facility and are not transferred into other states.

States can also have transitions that result in a return to the originating state.

Properties and Property Groups

The dependencies, methods, delegated restarter, and instance state mentioned above are represented as properties or property groups of the service or service instance. A service or service instance has an arbitrary number of property groups in which to store application data. Using property groups in this way allows the configuration of the application to derive the attributes that the repository provides for all data in the facility. The application can also use the appropriate subset of the service_bundle(4) DTD to represent its configuration data within the framework.

Property lookups are composed. If a property group-property combination is not found on the service instance, most commands and the high-level interfaces of libscf(3LIB) search for the same property group-property combination on the service that contains that instance. This feature allows common configuration among service instances to be shared. Composition can be viewed as an inheritance relationship between the service instance and its parent service.

Properties are protected from modification by unauthorized processes. See smf_security(5).

Snapshots

Historical data about each instance in the repository is maintained by the service management facility. This data is made available as read-only snapshots for administrative inspection and rollback. The following set of snapshot types might be available:

initial

Initial configuration of the instance created by the administrator or produced during package installation.

last_import

Configuration as prescribed by the manifest of the service that is taken during svccfg(1M) import operation. This snapshot provides a baseline for determining property customization.

previous

Current configuration captured when an administrative undo operation is performed.

running

The running configuration of the instance.

start

Configuration captured during a successful transition to the online state.

The svccfg(1M) command can be used to interact with snapshots.

Special Property Groups

Some property groups are marked as “non-persistent”. These groups are not backed up in snapshots and their content is cleared during system boot. Such groups generally hold an active program state which does not need to survive system restart.

Configuration Repository

The current state of each service instance, as well as the properties associated with services and service instances, is stored in a system repository managed by svc.configd(1M). This repository is transactional and able to provide previous versions of properties and property groups associated with each service or service instance.

The repository for service management facility data is managed by svc.configd(1M).

Service Bundles, Manifests, and Profiles

The information associated with a service or service instance that is stored in the configuration repository can be exported as XML-based files. Such XML files, known as service bundles, are portable and suitable for backup purposes. Service bundles are classified as one of the following types:

manifests

Files that contain the complete set of properties associated with a specific set of services or service instances.

profiles

Files that contain a set of service instances and values for the enabled property on each instance.

Service bundles can be imported or exported from a repository using the svccfg(1M) command. See service_bundle(4) for a description of the service bundle file format with guidelines for authoring service bundles.

A service archive is an XML file that contains the description and persistent properties of every service in the repository, excluding transient properties such as service state. This service archive is basically a 'svccfg export' for every service which is not limited to named services.

Legacy Startup Scripts

Startup programs in the /etc/rc?.d directories are executed as part of the corresponding run-level milestone:

/etc/rcS.d

milestone/single-user:default

/etc/rc2.d

milestone/multi-user:default

/etc/rc3.d

milestone/multi-user-server:default

Execution of each program is represented as a reduced-functionality service instance named by the program's path. These instances are held in a special legacy-run state.

These instances do not have an enabled property and, generally, cannot be manipulated with the svcadm(1M) command. No error diagnosis or restart is done for these programs.

See Also

svcs(1), inetd(1M), svcadm(1M), svccfg(1M), svc.configd(1M), svc.startd(1M), exec(2), fork(2), libscf(3LIB), strftime(3C), contract(4), service_bundle(4), user_attr(4), smf_bootstrap(5), smf_method(5), smf_restarter(5), smf_security(5)