+ <sect id="alternateinit">
+ <heading>Alternate init systems</heading>
+ <p>
+ A number of other init systems are available now in Debian that
+ can be used in place of <package>sysvinit</package>. Alternative
+ init implementations must support running SysV init scripts as
+ described at <ref id="sysvinit"> for compatibility.
+ </p>
+ <p>
+ Packages may integrate with these replacement init systems by
+ providing implementation-specific configuration information about
+ how and when to start a service or in what order to run certain
+ tasks at boot time. However, any package integrating with other
+ init systems must also be backwards-compatible with
+ <package>sysvinit</package> by providing a SysV-style init script
+ with the same name as and equivalent functionality to any
+ init-specific job, as this is the only start-up configuration
+ method guaranteed to be supported by all init implementations. An
+ exception to this rule is scripts or jobs provided by the init
+ implementation itself; such jobs may be required for an
+ implementation-specific equivalent of the <file>/etc/rcS.d/</file>
+ scripts and may not have a one-to-one correspondence with the init
+ scripts.
+ </p>
+ <sect1 id="upstart">
+ <heading>Event-based boot with upstart</heading>
+
+ <p>
+ Packages may integrate with the <prgn>upstart</prgn> event-based
+ boot system by installing job files in the
+ <file>/etc/init</file> directory. SysV init scripts for which
+ an equivalent upstart job is available must query the output of
+ the command <prgn>initctl version</prgn> for the string
+ <tt>upstart</tt> and avoid running in favor of the native
+ upstart job, using a test such as this:
+ <example compact="compact">
+if [ "$1" = start ] && which initctl >/dev/null && initctl version | grep -q upstart
+then
+ exit 1
+fi
+ </example>
+ </p>
+ <p>
+ Because packages shipping upstart jobs may be installed on
+ systems that are not using upstart, maintainer scripts must
+ still use the common <prgn>update-rc.d</prgn> and
+ <prgn>invoke-rc.d</prgn> interfaces for configuring runlevels
+ and for starting and stopping services. These maintainer
+ scripts must not call the upstart <prgn>start</prgn>,
+ <prgn>restart</prgn>, <prgn>reload</prgn>, or <prgn>stop</prgn>
+ interfaces directly. Instead, implementations of
+ <prgn>invoke-rc.d</prgn> must detect when upstart is running and
+ when an upstart job with the same name as an init script is
+ present, and perform the requested action using the upstart job
+ instead of the init script.
+ </p>
+ <p>
+ Dependency-based boot managers for SysV init scripts, such as
+ <prgn>startpar</prgn>, may avoid running a given init script
+ entirely when an equivalent upstart job is present, to avoid
+ unnecessary forking of no-op init scripts. In this case, the
+ boot manager should integrate with upstart to detect when the
+ upstart job in question is started or stopped to know when the
+ dependency has been satisfied.
+ </p>
+ </sect1>
+ </sect>
+
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