diff --git a/docs/PORTABILITY_AND_STABILITY.md b/docs/PORTABILITY_AND_STABILITY.md index 0caa5cc048..27562c17d8 100644 --- a/docs/PORTABILITY_AND_STABILITY.md +++ b/docs/PORTABILITY_AND_STABILITY.md @@ -120,7 +120,7 @@ And now, here's the list of (hopefully) all APIs that we have introduced with sy | `/run` | File hierarchy change | yes | yes | numerous | yes | OpenSUSE, Debian, ArchLinux | no | | [Generators](https://www.freedesktop.org/software/systemd/man/systemd.generator.html) | Subprocess | yes | yes | - | no | - | no | | [System Updates](https://www.freedesktop.org/software/systemd/man/systemd.offline-updates.html) | System Mode | yes | yes | - | no | - | no | -| [Presets](https://freedesktop.org/wiki/Software/systemd/Preset) | File format | yes | yes | - | no | - | no | +| [Presets](https://www.freedesktop.org/software/systemd/man/systemd.preset.html) | File format | yes | yes | - | no | - | no | | Udev rules | File format | yes | yes | numerous | no | no | partially | diff --git a/man/systemctl.xml b/man/systemctl.xml index e49a12a146..db4e2b2c65 100644 --- a/man/systemctl.xml +++ b/man/systemctl.xml @@ -793,9 +793,7 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err For more information on the preset policy format, see systemd.preset5. - For more information on the concept of presets, please consult the - Preset - document. + diff --git a/man/systemd.preset.xml b/man/systemd.preset.xml index 5697e50be7..cbd89daf16 100644 --- a/man/systemd.preset.xml +++ b/man/systemd.preset.xml @@ -32,28 +32,20 @@ Description - Preset files may be used to encode policy which units shall - be enabled by default and which ones shall be disabled. They are - read by systemctl preset (for more information - see - systemctl1) - which uses this information to enable or disable a unit according - to preset policy. systemctl preset is used by - the post install scriptlets of RPM packages (or other OS package - formats), to enable/disable specific units by default on package - installation, enforcing distribution, spin or administrator preset - policy. This allows choosing a certain set of units to be - enabled/disabled even before installing the actual package. + Preset files may be used to encode policy which units shall be enabled by default and which ones + shall be disabled. They are read by systemctl preset which uses this information to + enable or disable a unit. Depending on that policy, systemctl preset is identical to + systemctl enable or systemctl disable. - For more information on the preset logic please have a look - at the Presets - document. + systemctl preset is used by the post install scriptlets of rpm packages (or other OS + package formats), to enable/disable specific units by default on package installation, enforcing + distribution, spin or administrator preset policy. This allows choosing a certain set of units to be + enabled/disabled even before installing the actual package. For more information, see + systemctl1. - It is not recommended to ship preset files within the - respective software packages implementing the units, but rather - centralize them in a distribution or spin default policy, which - can be amended by administrator policy. + It is not recommended to ship preset files within the respective software packages implementing the + units, but rather centralize them in a distribution or spin default policy, which can be amended by + administrator policy, see below. If no preset files exist, systemctl preset will enable all units that are installed by @@ -175,6 +167,38 @@ disable * override all other preset policy files. + + Motiviation for the preset logic + + Different distributions have different policies on which services shall be enabled by default when + the package they are shipped in is installed. On Fedora all services stay off by default, so that + installing a package will not cause a service to be enabled (with some exceptions). On Debian all + services are immediately enabled by default, so that installing a package will cause its services to be + enabled right-away. + + Even within a single distribution, different spins (flavours, remixes, whatever you might want to + call them) of a distribution also have different policies on what services to enable, and what services + to leave off. For example, Fedora Workstation will enable gdm as display manager by + default, while the Fedora KDE spin will enable sddm instead. + + Different sites might also have different policies what to turn on by default and what to turn + off. For example, one administrator would prefer to enforce the policy of "sshd should + be always on, but everything else off", while another one might say "snmpd always on, + and for everything else use the distribution policy defaults". + + Traditionally, policy about which services shall be enabled were implemented in each package + individually. This made it cumbersome to implement different policies per spin or per site, or to create + software packages that do the right thing on more than one distribution. The enablement mechanism was + also encoding the enablement policy. + + The preset mechanism allows clean separation of the enablement mechanism (inside the package + scriptlets, by invoking systemctl preset) and enablement policy (centralized in the + preset files), and lifts the configuration out of individual packages. Preset files may be written for + specific distributions, for specific spins or for specific sites, in order to enforce different policies + as needed. It is recommended to apply the policy encoded in preset files in package installation + scriptlets. + + See Also @@ -182,6 +206,13 @@ disable * systemctl1, systemd-delta1 + + daemon8 + has a discussion of packaging scriptlets. + + Fedora page introducing the use of presets: + Features/PackagePresets. +