LISA '05 Paper
[LISA '05 Technical Program]
Solaris Service Management Facility: Modern System Startup and Administration
Jonathan Adams, David Bustos, Stephen Hahn, David Powell,
and Liane Praza
- Sun Microsystems, Inc.
Pp. 225-236 of the Proceedings of LISA '05:
Nineteenth Systems Administration Conference,
(San Diego, CA:
USENIX Association, December 2005).
Application uptime is critical to every administrator. The factors
which cause system downtime are often handled by the operating system,
but causes for application faults (e.g., software bugs, hardware
faults, or human errors) are not addressed by standard system
software. Recovery is left to humans, who may often compound the
problem due to misdiagnosis or simple error. While availability issues
have traditionally been addressed by expensive high-availability
clustering solutions, the increasing complexity of software stacks
requires a solution for all systems.
In addition to the challenges of managing availability of higher
level software, the modern operating system itself is composed of many
interdependent software entities. A failure in any one of these
components often cascades, causing failures in other components. A
complex software model with many interdependent elements makes
diagnosing failures very challenging for system administrators. The
traditional init.d script mechanisms for UNIX are only
a weak reflection of the intricate dependency relationships which
exist on every system.
We introduce the Service Management Facility (SMF) as a
comprehensive way to describe, execute, and manage software services.
SMF promotes the service to a first-class operating system entity,
without requiring modification of application binaries or changes to
the UNIX process model. It relieves the administrator from duties of
application failure detection and restart, and provides sophisticated
diagnosis tools when automatic repair is impossible.
As software running on a system becomes more complex, the
traditional separation of management of system startup from run-time
management becomes untenable. The reliability of modern hardware,
coupled with the ever-increasing complexity of modern software means
that applications are just as likely, if not more likely, to be the
point of failure on a system. Reboots are costly, especially on
A system administrator is expected to ensure that critical
applications are always running. This is sometimes done by manual
monitoring or an expensive to maintain home-grown tool, or the
administrator is expected to turn to software not well integrated with
the operating system - either sophisticated monitoring packages, or
expensive and often complex high-availability clustering software. The
unbundled solutions usually also focus on higher level applications,
and can neglect potential failures of core operating system daemons.
But, even higher level applications do not stand on their own. In
order to provide business-critical functionality, often two or more
pieces of software must be working and cooperating closely together.
Failure of even a less critical application can have unforeseen
consequences in important software.
In addition to basic availability concerns for software services,
the service management model needs to be significantly enhanced.
Without a common model and interface, it is very difficult to ask the
system even basic questions such as: "what's running?", "what's
broken?", and "what applications are available on this system?".
Application management is a fundamental task of all
administrators: managing applications should not require a bolt-on
solution. Driving the service management interface into the operating
system also brings significant benefits through encouraging evolution
of core operating system functionality to support the service, and
creating a truly common interface for all user software: operating
system daemons and third party products alike.
The UNIX service management model has not evolved significantly
beyond the traditional process model coupled loosely with service
startup scripts, and is stretched in trying to meet modern system
administration demands. The lack of functionality is costly for
administrators, who must spend significant effort monitoring and
managing systems that provide no fundamental abstractions to allow
SMF directly addresses all of these administration gaps and
provides an integrated solution for service delivery and management on
UNIX systems. SMF defines a fundamental service model which is used to
control system startup, introduces a management interface for system
and application services, and delivers diagnosis and restart
capabilities for all services to maximize application availability.
Background and Related Work
The traditional System V and BSD style
init.d/rc systems provide an extremely
flexible mechanism for initiating arbitrary processes during system
startup. For all of the flexibility provided, a number of deficiencies
are apparent. We'll enumerate these deficiencies in terms of the
System V implementation, but analogous problems exist in the BSD style
No systematic way to list services. As the init.d
system does not even encourage, much less enforce a 1:1 mapping of
system services to init.d scripts, a simple
ls of rc directories is never
sufficient to get a full list of services provided by the system. The
services required to start core operating system components are often
the most opaque to the administrator.
No persistent mechanism to indicate to the system whether a service
should be running or not. Upgrade of software components often updates
or even re-creates the corresponding rc script,
overwriting administrative customizations such as attempts to disable
No formal dependency management interfaces. System components are
usually very sensitive to ordering changes. The System V
lexicographical ordering provides some latitude for the third-party
service. Service developers can have their script run at a certain
point during startup (before some services and after others) by giving
the script an appropriate name. But, the lack of explicit dependency
specification for a service makes modifications to the ordering of
core system services fragile, and leads to unexpected behaviour.
Incomplete manual restart capabilities. The individual
init.d scripts are not necessarily stand-alone or
idempotent. The administrator is not expected to execute all of the
init.d scripts manually, so there is no simple way to
restart many individual services without understanding the intricacies
of their implementation. Closely cooperating services compound the
problem; restart of one may require restart of its closely coupled
dependent services. The init.d system provides no
mechanism to determine service interdependencies, so significant
administrative expertise is required to restart individual services
without a reboot.
Nonexistent automatic restart capabilities. The init.d
system does not include automatic detection and restart of failed
components. Detection and restart is left to orthogonal mechanisms
such as inittab and inetd.conf.
Lack of correlation between processes and services. Services are
becoming increasingly sophisticated; the traditional UNIX model of a
single daemon process as the entirety of a service is no longer
adequate. Multiple processes are correlated into service boundaries by
administrative expertise rather than being programmatically
represented as a first-class object. The UNIX process model
complicates the analysis - daemons are often reparented to
init and lose their parent-child association in the
Ticking configuration time bombs. There is no formal association
between the current status of the system and the expected state when
the system is restarted because starting a service has no impact on
its settings on reboot. In addition, there is no systematic way to
determine current versus configured state, so a reboot often leads to
unpleasant surprises due to un-configured or mis-configured services.
For rigidly specified service models, such as
inetd, the deficiencies can be more easily addressed.
However, a complete system management architecture must provide a
model sufficiently rich for all system services. SMF addresses each of
these deficiencies for general software services.
Previous work in this area aims primarily to improve deficiencies
of the init.d/rc system in system
startup and manual service enable, disable and restart, up to and
including a more formal statement of dependencies [1, 2, 3]. This work
helps administrators gain better visibility into system service
configuration and provide slight enhancements to administrative tools.
However, if application availability is the crucial measurement, these
sorts of enhancements only aid insofar as they slightly reduce the
chances of administrative error.
Some recent efforts [4, 5] are more sophisticated and include
simple service restart. The service can be restarted either when
requests for that service come in, or restarted when the service exits
unexpectedly. However, these efforts assume a single process is the
primary provider of service, which is insufficient for a large class
of business-critical applications.
Altering system service management is guaranteed to cause a change
in administrative procedures. Changing something as fundamental as the
init.d system requires administrators to spend time
learning the new management paradigm. Thus, we took an ambitious
approach so that the significant changes happened all together, rather
than creating an incremental education cost over many software
releases. The redesign of service management procedures must be
comprehensive, and consider the full range of administrative
procedures, software errors, and hardware errors.
The most fundamental requirement of this work is a simple, common
model for all services. Services must be able to encompass nearly all
capabilities of the system - simple daemons, network services, complex
databases, and even non-process-based services such as dump device
configuration. The management framework must be flexible enough to
allow common actions to be done easily and with no required
administrative knowledge of the service implementation. A common model
for all application and system services is required in order to
thoroughly leverage administrator expertise; an administrator should
be able to manage syslogd using the same basic
commands as telnetd.
The service model must be extensible. New types of services,
increased diagnosability, and expanded meta-configuration should be
easy to support with no required enhancements to existing service
Relationships between services are more complex than start time
requirements. Many services are written carefully to be resilient to
failure of their dependencies. For example, a well written networking
application does not need to be restarted when a transient nameservice
failure occurs. However, starting even a defensively-coded application
without nameservice availability is usually futile. Thus, a rich
dependency declaration is required to encompass both startup and
Services then are restarted according to their dependencies
following either hardware or software failure. A service restart must
be attempted following any type of failure, such as a critical process
exit, an uncorrectable memory error or other hardware error, a
software coredump or premature exit, or an administrator accidentally
killing the wrong process. Any dependents of that service must be
restarted if they specify intolerance to dependency failures.
When a service cannot be automatically repaired after a fault, the
system must provide significant aids to manual diagnosis, and trace
failure back to the responsible component. When software failures can
be traced back to the initial fault, this information as well as as
much data as possible about the specific fault must be provided to the
administrator so that he can spend his time repairing the fault rather
than debugging an error in a dependent service. For example, if an
application cannot start because the filesystem containing the
application data was unable to mount, the system should point to the
filesystem as the root cause of the fault, rather than incorrectly
indicting the application.
The other critical component of a service management interface is
its handling of service configuration data. We identified a set of
meta-configuration, which is similar across a large set of services.
For example, one critical pieces of meta-configuration captures
whether a service is supposed to be running on a specific system.
Common tools should be provided for meta-configuration, while still
retaining the flexibility for services to provide their own complex
Meta-configuration must be available via a common command set and
API across all services. This allows rapid development of higher-level
administration tools which need no application knowledge to perform
common tasks. Service-specific configuration can also be stored in a
format accessible by this API, but the choice to transition to the new
configuration store is up to the application developer depending on
their compatibility requirements. Through the common commands,
configuration rollback is provided. An administrator should be able to
undo configuration or meta-configuration changes which rendered a
A few constraints were also required for a practical
implementation in an operating system with strong compatibility
No application binary changes required for basic participation in the
Compatibility for existing init.d services. The vast
majority of services must continue to work, to account for lag time in
new feature adoption by software developers.
Extending UNIX Processes to Software Services
SMF formalizes software "services", and introduces the tools to
create, observe, manage and automatically restart them. A service is a
long-lived software object (typically, a daemon) with a name, a clear
error boundary, start and stop methods, and dependency relationships
to other services on the system.
A service may be composed of zero, one, or many processes. A
comprehensive software service model must allow all of these process
models, and take each into account when defining failures. We'll first
consider a typical UNIX service which only has one process. These
services are relatively straightforward to manage and monitor. The
single process makes process-to-service mapping easy to understand, as
no complex lineage from parents to children needs to be tracked. If
the process exits, the service is no longer being provided and must be
restarted. Still, without a new mechanism to track process faults,
most monitoring implementations would require services forgo the
traditional reparent-to-init step.
Even simple services can consist of multiple processes. For
example, the Sendmail service usually includes two processes. Failure
of either process should cause the service to be restarted.
Traditional models for determining the relationship between these two
processes fall down: they both re-parent themselves to
init, breaking monitoring implementations which rely
on the parent-child relationship. Aside from the process name, it is
difficult to tell they're both part of the same service.
Finally, we have a set of services which only appear transiently
during the startup process. Usually, they exist to execute a command
or small set of commands which change configuration state, such as
informing the kernel about certain configuration parameters. It is
important for SMF to understand a priori that a lack of long-running
processes in these transient services does not constitute a
In order to monitor the health for all three types of services,
SMF introduces a kernel interface called a contract. A process
contract allows a userland process to register an interest in a
process and all of its children. The process receives reliable events
when important changes occur, such as when all processes in the
contract exit, a hardware error occurs in any of the processes, any
processes in the contract coredump, or any process in the contract
receives a fatal signal. All processes on the system must belong to a
process contract, and all children of a process are part of the same
contract until one creates a new contract.
Service restarters are responsible for managing software
services. A restarter can use process contracts to receive and respond
to fault events for a service. Usually, a restarter will write a
process contract for each new service it creates. Thus, events for
each service will be sent individually to the restarter, where it can
make decisions about how to respond to contract events and
administrative requests. Each process can fail separately, but it is
the restarter's job to decide how a process failure should affect the
Figure 1: Contract model for software
A restarter determines how to interact with a service through its
meta-configuration, which is stored in the SMF repository. The
SMF repository stores persistent configuration and meta-configuration
values as well as shorter-lived status information about each service.
Each service has a common set of meta-configuration:
The service name, in the form of a Fault Managed Resource Identifier
(FMRI) is the unique identifier of the service on the system. The full
FMRI for the sendmail service is: svc:/network/smtp:
sendmail, but abbreviations like "sendmail" are available
for interactive use.
Service dependencies specify the relationships between
Method specifications tell the restarter how to invoke the
services, and may include invocations for start, stop, etc.
The restarter defined by the service is responsible for starting,
stopping, and restarting the service. Most services are managed by the
default restarter, svc.startd. We've also implemented
inetd as a service restarter.
Services can optionally include localized, human readable descriptions
and documentation references.
A service may also use the SMF repository to store simple
configuration information. This allows application and system service
developers to avoid maintaining configuration file parsers for small,
We developed a comprehensive state model for managing services,
which are always in one of the following states: uninitialized,
offline, online, degraded, disabled, and maintenance. These states
have a consistent definition regardless of the service model.
|Uninitialized|| The initial state for all services. After
evaluation by its restarter, the restarter will move the service to a
maintenance, offline, or disabled state.
|Disabled|| The service has been disabled and is not running.
|Offline|| The service is enabled, but is not yet running.
Often, a service will remain offline due to an unsatisfied dependency.
|Online|| The service is enabled, has started successfully
and is currently running.
|Degraded|| The service is enabled, currently running but may
be functioning at a limited capacity (e.g., reduced performance). The
precise definition of degraded is service-specific.
|Maintenance|| The service is unavailable and cannot be
automatically repaired by SMF. Administrative intervention is required
to repair the service and clear the fault.
Table 1: State model for
Services transition between these states either because of
administrative action (system startup, service enable, service
disable), or service error (core dump, starting too rapidly, hardware
fault). The service's ability to transition to a given state is always
additionally influenced by the states of its dependencies.
To implement the service state model, SMF includes service
restarters, which are themselves system services (and hence subject to
the state model). In our current work, a master restarter
(svc.startd) and one delegated restarter
(inetd) have been developed. While each of these are
concerned with the restart of UNIX processes, the restarter
architecture also allows implementation of non-process-based service
models . Each service restarter is responsible for defining
appropriate transitions between the available SMF states.
Figure 2: svc.startd state
The meta-configuration and other simple service configuration are
delivered onto the system by a small XML file, known as a service
manifest. When the system starts up, the individual manifests
are imported into the main SMF repository. The configuration of the
system, including administrative customizations and run-time service
data is stored in the repository and accessed by a common set of
commands and APIs. The repository also provides the transactional
semantics required for recovery on failure as well as the previous
configuration snapshots which allow for configuration rollback.
In order to deliver an SMF-aware service, the administrator or
software developer is required to create a service manifest. The
manifest must include the meta-configuration for the service: a
service name, the required methods, all dependency information,
documentation references, and any other configuration to be stored in
SMF currently provides two restarters: svc.startd,
the master restarter, and inetd, the inet service
restarter. Both restarters require service definition through a
To provide a smooth upgrade path, service manifest creation can be
an automatic step for inetd.conf services. We provide
the inetconv utility to convert entries from
inetd.conf to service manifests on operating system
upgrade and allow administrators to convert entries subsequently added
to the file. This is made easy by the well-specified service model for
inetd services, and the fact that their dependencies
are well known: inetd itself must be started, and rpc
services require rpcbind.
Manifest creation for init.d scripts remains a
manual process. The set of information required is well-defined,
however two specific questions cannot be answered programmatically:
What are this service's dependencies? While we might be able to
imagine a run-time checker or code analyzer for dependencies, these
dependencies are often subtle and strongly tied to configuration.
Automatic application dependency analysis would be a fascinating
research topic of its own. The service author is usually best
equipped to define the dependencies precisely. However, any consumer
of the service can usually specify a dependency set that is sufficient
for normal operation.
What is this service's runtime behaviour? Does it have long-running
processes that must be monitored, or is a lack of associated processes
<service_bundle type='manifest' name='SUNWcsr:utmpd'>
<create_default_instance enabled='true' />
<service_fmri value='svc:/milestone/sysconfig' />
<service_fmri value='svc:/milestone/multi-user' />
<stability value='Unstable' />
<loctext xml:lang='C'> utmpx monitoring
<manpage title='utmpd' section='1M' manpath='/usr/share/man' />
<manpage title='utmpx' section='4' manpath='/usr/share/man' />
Figure 3: utmpd
The service manifest author is required to specify dependencies in
the manifest. Dependencies define service startup order as well as the
restart relationships between services. A dependency is said to be
satisfied if all conditions of its definition are met. There can be
multiple dependencies for each service and each dependency may declare
interest in multiple services. Two attributes of a dependency aside
from the actual services in the dependency must be defined. The
grouping specifies how the state of the services specified in
the dependency are evaluated to determine whether a dependency is
require_all: all named services are running (online or
require_any: at least one named service is running (online or
optional_all: all named services must be either running (online
or degraded), disabled, in maintenance, or not present on the system
exclude_all: all named services must be either disabled,
offline, in maintenance, or absent
The restart_on property determines which events should
cause the service to be stopped:
none: required only when the service is started
error: stop the service if the dependency fails due to hardware,
software or administrative error
restart: stop the service if the dependency stops for any reason
refresh: stop the service if the dependency stops or is refreshed
Explicit dependency specification makes parallel service startup
easy, regardless of whether the system is booting for the first time,
or if a set of services had failed and are being restarted. Services
are always started as soon as their dependencies are satisfied, so
maximum parallelism for starting services is always achieved.
Unifying application deployment also provides a single location
for access to advanced features. A service can be run with limited
Privileges , or as an unprivileged or non-root user. Service
management privileges may be given to authorized users without giving
them full root access. A service may be bound to specific resource
management limit and goal sets. All of this can be specified as
service configuration with no code changes to the application itself
(see Figure 4). Management of Solaris Zones  is simpler as SMF is
available to each zone administrator.
# svccfg -s <svc> setprop start/user = astring: daemon
# svccfg -s <svc> setprop start/group = astring: daemon
# svcadm refresh <svc>
# svcadm restart <svc>
Figure 4: Configuring a service to run as
"daemon" user and group.
STATE STIME FMRI
legacy_run May_02 lrc:/etc/rc3_d/S81volmgt
legacy_run May_02 lrc:/etc/rc3_d/S84appserv
legacy_run May_02 lrc:/etc/rc3_d/S90samba
online May_02 svc:/system/svc/restarter:default
online May_02 svc:/network/pfil:default
online May_02 svc:/network/loopback:default
online May_02 svc:/system/filesystem/root:default
online May_02 svc:/system/filesystem/usr:default
Figure 5: Abbreviated svcs output,
including legacy services.
$ svcs -x
svc:/network/smtp:sendmail (sendmail SMTP mail transfer agent)
State: maintenance since Tue May 10 18:35:41 2005
Reason: Method failed repeatedly.
Impact: This service is not running.
Figure 6: Checking the sendmail
The primary benefit a unified service management framework brings
to system and service administration is a meaningful system-level view
of all critical applications (see Figure 5). Services in an unexpected
state are sorted at the bottom of the output for simple human
A primary goal of the SMF administrative model is to make common
questions about services easy to answer and make common system
administration tasks simple to perform. To evaluate the simplicity of
the SMF model, the following provides examples of a few of these
questions that were particularly difficult to answer in the
init.d and inetd models prior to SMF.
What processes make up this service?
$ svcs -p sendmail
STATE STIME FMRI
online May_06 svc:/network/smtp:sendmail
May_06 9456 sendmail
May_06 9458 sendmail
What's wrong with my system? (This will be covered in more
detail in the next section.) See Figure 6. What services does my
service require in order to start? See Figure 7. Which
services won't be able to run if I disable this service? See
Figure 8. What services are available on this system? See
Messaging is also under the control of the administrator rather
than the service. Messages previously emitted to console are stored in
a per-service logfile, where they can be perused as part of post-mortem
debugging or other diagnosis. They won't be lost to an
insufficient terminal buffer size.
SMF defines a specific set of common administrative actions which
can be applied to services:
enable - Mark the service as enabled and start the service
after all dependencies are satisfied.
disable - Mark the service as disabled, stop the service, and
do not allow it to start again.
refresh - Reload service configuration and run the service's
refresh method (if a refresh method is defined by the service).
$ svcs -d sendmail
STATE STIME FMRI
online Aug_12 svc:/system/identity:domain
online Aug_12 svc:/system/filesystem/local:default
online Aug_12 svc:/network/service:default
online Aug_12 svc:/milestone/name-services:default
online Aug_12 svc:/system/filesystem/autofs:default
online Aug_12 svc:/system/system-log:default
Figure 7: Determining services needed by
$ svcs -D system-log
STATE STIME FMRI
disabled Aug_12 svc:/system/auditd:default
disabled Aug_12 svc:/application/print/server:default
disabled Aug_12 svc:/network/rarp:default
online Aug_12 svc:/milestone/multi-user:default
online 5:55:34 svc:/network/smtp:sendmail
Figure 8: Determining services which require
$ svcs -a
disabled Aug_12 svc:/network/iscsi_initiator:default
disabled Aug_12 svc:/system/metainit:default
disabled Aug_12 svc:/network/ipfilter:default
disabled Aug_12 svc:/network/rpc/nisplus:default
disabled Aug_12 svc:/network/nis/server:default
disabled Aug_12 svc:/network/ldap/client:default
Figure 9: Available service listing.
$ grep lianep /etc/user_attr
$ svcs sendmail
STATE STIME FMRI
disabled 18:51:56 svc:/network/smtp:sendmail
$ svcadm enable sendmail
$ svcs sendmail
STATE STIME FMRI
online 18:52:43 svc:/network/smtp:sendmail
$ svcadm refresh sendmail
$ svcs sendmail
STATE STIME FMRI
online 18:52:55 svc:/network/smtp:sendmail
$ svccfg -s sendmail delpg autofs
svccfg: Permission denied.
Figure 10: Delegating service management
restart - Stop the service, then start it after its
dependencies are satisfied.
clear - Mark a service in the maintenance state as repaired,
and if it is enabled allow it to start after all its dependencies are
Administrators use svcadm to perform these administrative actions.
Administrative intent is always preserved; disabling a service is
guaranteed to persist across even patch and upgrade boundaries, where
that was difficult in the past. The separation of administrative
action and service state allows easier evaluation when system state
doesn't match the administrative desire.
The use of a single API to take administrative action and change
service configuration allows one point for security enforcement. Thus,
SMF interoperates intimately with Role Based Access Control 
mechanisms. It is easy to give a user just the ability to take action
on a service (e.g., restart the service), but not change the service's
configuration (see Figure 10). An administrator may also delegate
authorizations with more granularity, giving privilege for an
application administrator to only manage and change the configuration
of a single service .
Finally, system security can be easily configured by creating a
profile, which explicitly specifies which services are enabled
and disabled on a system. To satisfy the common system configuration
goal of no unencrypted network login services running, we provide the
limited networking profile. Applying this profile explicitly disables
all unencrypted network login services and enables other important
services like ssh (see Figure 11).
# svcs telnet
STATE STIME FMRI
online 17:49:15 svc:/network/telnet:default
# cd /var/svc/profile/
# cat generic_limited_net.xml
<service_bundle type='profile' name='generic_limited_net'
<service name='network/ssh' version='1' type='service'>
<instance name='default' enabled='true'/>
<service name='network/telnet' version='1' type='service'>
<instance name='default' enabled='false'/>
# svccfg apply generic_limited_net.xml
# svcs telnet
STATE STIME FMRI
disabled 17:49:40 svc:/network/telnet:default
Figure 11: Viewing and applying the limited
$ svcs -xv
svc:/system/filesystem/local:default (Local filesystem mounts)
State: maintenance since Tue Sep 27 19:03:43 2005
Reason: Start method exited with $SMF_EXIT_ERR_FATAL.
Impact: 23 dependent services are not running:
Figure 12: Service diagnosis of filesystem mount
Service Diagnosis and Self-Healing
svcs -x is a quantum leap forward in diagnosing
problems with systems. It provides a very powerful paradigm. It
describes what's going on in plain language with simplified output. It
includes documentation references, as direct access to more
information speeds the repair process. It points to an online
knowledgebase; the website link included in the output contains the
most up-to-date information on how to resolve the specific problem
seen. Finally, svcs -x gives an assessment of the
impact of each problems. If the specific issue effects no other
services, that is stated explicitly. If other services are affected,
svcs -xv will list them.
As the system (through dependency information) can determine the
root cause of the problem, it can point the administrator directly to
the component that must be repaired (see Figure 12).
In many cases, though, the administrator never needs to handle an
error manually. Failure of a service due to hardware error, software
bug, or administrative error can usually be resolved by restarting the
service. This is handled automatically, with no administrative
intervention. SMF also logs the error cause, to the extent it is known
at the time of failure. This automatic recovery significantly reduces
To implement service restartability, SMF needed a way to detect
when an error occurred in the service. Contracts provide a generic
mechanism to express a relationship between a process and the kernel-managed
resources it depends upon. The process contract allows
development of sophisticated restarters, which create a fault boundary
around a set of processes, and receive and respond to events on
processes within that boundary.
Implicit in service recovery is that the framework itself must
also be fully restartable in the face of failures. An error of any
user-land framework component all the way back to init
can be caught, and the framework component itself will be restarted
(see Figure 13). A transactional repository is required in order to
implement the algorithms which recover from failure at any point.
Figure 13: SMF framework restart
Systems with sophisticated hardware error handling  make
software recovery after error even more critical. Prior to SMF, the
operating system developer when handling a hardware failure was given
only a few unenviable options: kill the affected process and risk
cascading failure, or restart the entire system. The operating system
could not determine the broader effect of a faulted cell on a DIMM
without inter-service dependency information. SMF manages error flow
between services so that failures can be handled gracefully, by
shutting down only affected processes and services which depend upon
The first version of the Service Management Facility is an
integrated component of the Solaris 10 Operating System, released in
January 2005. Themost recent copy of Solaris may be obtained free of
charge at http://www.sun.com/software/solaris/.
The Service Management Facility is also an integral part of
OpenSolaris, which may be downloaded as source or binaries at
http://opensolaris.org/os/. The OpenSolaris SMF community contains
information and discussion about service development and management in
Solaris and OpenSolaris: http://opensolaris.org/os/community/smf/.
The first proof of concept and vetting of the design occurred when
transitioning approximately 100 system services from their
init.d script components into SMF. We wanted to
confirm certain aspects of the SMF design, as well as take advantage
of SMF benefits for Solaris service administration. The majority of
services delivered as part of the Solaris operating system were
migrated to SMF as part of its initial integration. We'll explore this
case study here.
A small engineering team was responsible for creating nearly all
of the 100 manifests for system services. A major lesson was that once
a developer gains familiarity with the SMF model, manifest creation
tends to take no more than a few hours per service, often including
necessary testing. Experience with one manifest is directly leveraged
for subsequent manifest creation. The fundamentals for basic service
cooperation in SMF are relatively easy to grasp and do not seem to
require significant training. The more sophisticated aspects of the
service model tend to not be explored by the average service author,
which we interpreted as success in our goal to make simple services
easy to define.
As expected, the most challenging part of manifest creation was
researching proper dependencies for each service. Sometimes the
initial dependency analysis was incomplete - but, both point fixes for
significant problems and longer term dependency additions to fill gaps
were easy to perform.
We learned that someone familiar with the service implementation
will be able to write a significantly better manifest than someone
merely conversant in the service. A service manifest written by an
end-user of the software is sufficient for that user's configuration,
but not all potential uses and configuration of the service.
Encouraging service authors to write manifests for their software has
significant value, even when a basic manifest has already been
Console interaction was more of a challenge than anticipated. When
system startup was serial, console ownership was easy as it simply
passed linearly from one script to another. SMF's parallel startup
required tracking the console owner at all times, in case a system
maintenance mode (also known as sulogin) was required
to repair the system. The console ownership problem is a compelling
reason for Solaris to provide access to the standard console login
prompt as early in the boot sequence as possible. This convention is
particularly helpful in a repair scenario because as much of the
system as possible is available for use during the repair, rendering
the repair environment less restrictive and more familiar.
Confirming the SMF design with critical system services started
early in the boot sequence was likely a bit painful for the very early
adopters. However, the lessons learned through actual service
debugging informed significant usability enhancements which may not
have been given the attention they deserved had SMF been an optional
feature used only for a small subset of services.
A full-featured application and system service management
infrastructure must reduce management complexity, increase application
availability, and save administrators time. In order to provide all of
these capabilities for a wide range of application models, the service
must be elevated to a first-class administrative object which can be
observed and managed. The Service Management Facility provides all of
these benefits while requiring no changes to application binaries.
SMF reduces complexity by unifying and simplifying common
administrative tasks across a broad set of applications. It increases
application availability by detecting many critical errors and
recovering from them automatically. Finally, it saves administrators
time; when automatic recovery from failures is impossible, a complete
management interface guides the administrator to the faulty component.
Jonathan Adams joined Sun Microsystems, Inc. in Menlo Park four
years ago, where he is a software developer in the Solaris Kernel
Development group. His areas of expertise include memory allocation,
inter-process communication, and debuggability. Reach him
electronically at firstname.lastname@example.org.
David Bustos graduated from the California Institute of Technology
in 2002 with a BS in computer science. Since then he has worked in the
Solaris operating system engineering group at Sun Microsystems, in
Menlo Park, California.
Stephen Hahn is a Senior Staff Engineer in the Solaris Kernel
Technologies group at Sun Microsystems. His recent work has been
focused on service and resource management at the operating system
level, particularly in building foundations for automated resource
managers. His research interests are broad, and include describing
meaningful application interdependencies, predictable systems
behaviour, open source development processes, and implementing high
performance sort algorithms. He received his Ph.D. in Theoretical
Physics from Brown University, before joining Sun in 1997.
David Powell is a member of the Solaris kernel group at Sun
Microsystems. In his six years at Sun, he has worked to improve the
debuggability, availability, and approachability of Solaris,
specifically focusing on inter-process communication and expressing
dependencies between system resources and their consumers. He received
his Sc.B. in Computer Science from Brown University
Liane Praza is a Staff Engineer in the Solaris Kernel Development
group at Sun Microsystems. She's been at Sun since 1997, with areas of
of expertise including the Solaris administration model, service and
resource management, self-healing services, and clustered devices and
filesystems. She received her B.S. in Computer Science from Purdue
University. Reach her electronically at email@example.com.
The SMF project was the work of a larger group of people than this
paper represents, and we are grateful to everyone who worked to make
this project possible. Dan Price, Dave Linder, and our USENIX
shepherd, Tom Limoncelli, provided invaluable feedback and
encouragement for this paper.
 Mewburn, Luke, "The Design and Implementation of the NetBSD rc.d
system," Proceedings of the FREENIX Track: 2001 USENIX Annual
Technical Conference, 2001.
 Gooch, Richard, "Advanced Boot Scripts," Proceedings of
the Ottawa Linux Symposium, June, 2002.
 Bernstein, D. J., Daemontools, http://cr.yp.to/daemontools.html.
 Skinner, Glenn, et al., "A Service Management Facility for
the Java Platform," Proceedings of the 2005 IEEE Services
Computing Conference, 2005.
 Shapiro, Michael W., "Self-Healing in Modern Operating
Systems," ACM Queue, Vol. 2, Num. 8, 2004.
 Candea, George, et al., "Recursive Restartability: Turning
the Reboot Sledgehammer into a Scalpel," Proceedings of the 8th
Workshop on Hot Topics in Operating Systems, 2001.
 Price, Daniel, et al., "Solaris Zones: Operating System
Support for Consolidating Commercial Workloads," Proceedings of
the 18th Large Installation System Administration Conferences (LISA,
 Brunette, Glenn, Restricting Service Adminisration in the
Solaris 10 Operating System, http://www.sun.com/blueprints/0605/819-2887.pdf.
 Sun Microsystems, Inc., System Administration Guide:
Security Services, http://docs.sun.com/app/docs/doc/816-4557.