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Diffstat (limited to 'man/systemd.preset.xml')
| -rw-r--r-- | man/systemd.preset.xml | 75 |
1 files changed, 53 insertions, 22 deletions
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 @@ <refsect1> <title>Description</title> - <para>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 <command>systemctl preset</command> (for more information - see - <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>) - which uses this information to enable or disable a unit according - to preset policy. <command>systemctl preset</command> 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.</para> - - <para>For more information on the preset logic please have a look - at the <ulink - url="https://www.freedesktop.org/wiki/Software/systemd/Preset">Presets</ulink> - document.</para> - - <para>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.</para> + <para>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 <command>systemctl preset</command> which uses this information to + enable or disable a unit. Depending on that policy, <command>systemctl preset</command> is identical to + <command>systemctl enable</command> or <command>systemctl disable</command>. + + <command>systemctl preset</command> 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 + <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para> + + <para>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.</para> <para>If no preset files exist, <command>systemctl preset</command> will enable all units that are installed by @@ -176,12 +168,51 @@ disable *</programlisting> </refsect1> <refsect1> + <title>Motiviation for the preset logic</title> + + <para>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.</para> + + <para>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 <command>gdm</command> as display manager by + default, while the Fedora KDE spin will enable <command>sddm</command> instead.</para> + + <para>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 "<command>sshd</command> should + be always on, but everything else off", while another one might say "<command>snmpd</command> always on, + and for everything else use the distribution policy defaults".</para> + + <para>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.</para> + + <para>The preset mechanism allows clean separation of the enablement mechanism (inside the package + scriptlets, by invoking <command>systemctl preset</command>) 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.</para> + </refsect1> + + <refsect1> <title>See Also</title> <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry> </para> + + <para><citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>8</manvolnum></citerefentry> + has a discussion of packaging scriptlets.</para> + + <para>Fedora page introducing the use of presets: + <ulink url="https://fedoraproject.org/wiki/Features/PackagePresets">Features/PackagePresets</ulink>. + </para> </refsect1> </refentry> |