From Fedora Project Wiki
(Note conflict between manual configuration and hardware enablement.)
(Mostly complete)
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== Enabling Services by Default ==
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== What is a Service? ==
Only services that meet all criteria below are permitted (but not required) to be enabled by default on package installation.
 
 
 
 
For the purposes of this document, a "service" is defined as one or more of:
 
For the purposes of this document, a "service" is defined as one or more of:
 
* A daemon or process started using a [http://www.freedesktop.org/software/systemd/man/systemd.service.html systemd service unit].
 
* A daemon or process started using a [http://www.freedesktop.org/software/systemd/man/systemd.service.html systemd service unit].
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Note that this includes processes which are not persistent.  If something started by a systemd service unit runs for a short period of time and then exits, it is still a service.  An example would be <code>iptables</code>.
 
Note that this includes processes which are not persistent.  If something started by a systemd service unit runs for a short period of time and then exits, it is still a service.  An example would be <code>iptables</code>.
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== Enabling Services by Default ==
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Only services that meet all criteria below are permitted (but not required) to be enabled by default on package installation.
  
 
=== Must not alter other services===
 
=== Must not alter other services===
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=== Must not require manual configuration to function ===
 
=== Must not require manual configuration to function ===
The service must not require configuration before it starts properly.  If the end-user/administrator must make some specific configuration change before the service is able to start without error and provide useful functionality then it MUST NOT be enabled by default.
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The service must not require configuration before it starts properly.  If the end-user/administrator must make some specific configuration change before the service is able to start without error then it MUST NOT be enabled by default.
  
XXX So... should we allow services to start by default which do nothing but exit cleanly if not configured? If not, then what about things which only function on some hardware?  That would conflicts directly with the later rule about hardware enablement.
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XXX Note that this allows services to start by default as long as they simply exit without error until they have been configured. I can't decide if this is a good thing, but to do otherwise could conflict with hardware support services below.
  
 
=== Must not listen for outside connections ===
 
=== Must not listen for outside connections ===
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Some hardware requires some additional service to be started in order to be useful.  This may come in the form of a non-persistent setup process or in the form of a continuously-running service.  If the service can be hardware activated to only start when the relevant hardware is present and do nothing when not present, and otherwise it meets the above requirements, then it SHOULD be enabled by default upon package installation.
 
Some hardware requires some additional service to be started in order to be useful.  This may come in the form of a non-persistent setup process or in the form of a continuously-running service.  If the service can be hardware activated to only start when the relevant hardware is present and do nothing when not present, and otherwise it meets the above requirements, then it SHOULD be enabled by default upon package installation.
  
If the service cannot be hardware activated, but it is possible to configure it such that it  
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If the service cannot be hardware activated, but it is possible to configure it such that it will exit without error and without marking the service as "failed" according to systemd, then it SHOULD be enabled by default upon package installation.  This clean exit may be accomplished through [https://www.freedesktop.org/software/systemd/man/systemd.unit.html#ConditionArchitecture=| systemd conditionals], by having the service (or a wrapper script) perform hardware detection and exit without indicating an error, or via other similar means.
 
 
 
 
Because full and automatic hardware support is desirable, such services SHOULD start automatically if that is possible without violating the above requirements. 
 
 
 
It is preferred that such services simply be hardware-activated if possible so that they only start when the relevant hardware is present.
 
 
 
If such services meet the above requirements and do
 
 
 
 
 
 
 
* They meet the above requirements for default services.
 
* They
 
 
 
If, when run on systems which do not possess the relevant hardware, those services exit cleanly, without error and without marking the service as "failed" from the perspective of systemd then those services SHOULD be enabled by default.
 
 
 
XXX That's a tortuous sentence.
 
 
 
 
 
 
 
* Manual configuration is not required (as above)
 
 
 
 
 
 
 
  
Services which suport
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If there is value in the service optionally failing in some instances (for example, when hardware which is expected to be present is removed or stops functioning) then this behavior MAY be made available using one or more of the following methods:
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* An opt-in mechanism involving a userspace tool with proper documentation.
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* The saving of state in permanent storage (an appropriate location in /var) to aid in detecting the failure.
  
 
== Approved Exceptions ==
 
== Approved Exceptions ==

Revision as of 23:09, 18 July 2018

What is a Service?

For the purposes of this document, a "service" is defined as one or more of:

Note that this includes processes which are not persistent. If something started by a systemd service unit runs for a short period of time and then exits, it is still a service. An example would be iptables.

Enabling Services by Default

Only services that meet all criteria below are permitted (but not required) to be enabled by default on package installation.

Must not alter other services

Installation of the package providing the unit auto-started by this preset may not change the behavior of any other service running (or potentially running) on the system.

Must not require manual configuration to function

The service must not require configuration before it starts properly. If the end-user/administrator must make some specific configuration change before the service is able to start without error then it MUST NOT be enabled by default.

XXX Note that this allows services to start by default as long as they simply exit without error until they have been configured. I can't decide if this is a good thing, but to do otherwise could conflict with hardware support services below.

Must not listen for outside connections

The service must not listen on a network socket for connections originating on a separate physical or virtual machine.

D-BUS services and hardware-activated services generally meet this requirement.

Hardware Support Services

Some hardware requires some additional service to be started in order to be useful. This may come in the form of a non-persistent setup process or in the form of a continuously-running service. If the service can be hardware activated to only start when the relevant hardware is present and do nothing when not present, and otherwise it meets the above requirements, then it SHOULD be enabled by default upon package installation.

If the service cannot be hardware activated, but it is possible to configure it such that it will exit without error and without marking the service as "failed" according to systemd, then it SHOULD be enabled by default upon package installation. This clean exit may be accomplished through systemd conditionals, by having the service (or a wrapper script) perform hardware detection and exit without indicating an error, or via other similar means.

If there is value in the service optionally failing in some instances (for example, when hardware which is expected to be present is removed or stops functioning) then this behavior MAY be made available using one or more of the following methods:

  • An opt-in mechanism involving a userspace tool with proper documentation.
  • The saving of state in permanent storage (an appropriate location in /var) to aid in detecting the failure.

Approved Exceptions

Some services which are permitted to be enabled by default as specific exceptions. Services that should be enabled by default throughout all of Fedora must be approved by FESCo. Services that should be enabled or disabled by default only on one or more of the Fedora Editions must be approved by those Editions' Working Groups.

Example:

  • FESCo approves openssh-server to run by default on Fedora in general.
  • Workstation WG approves openssh-server to be disabled by default on the Workstation Edition.