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dev-manual: Added info to "Selecting an Initialization Manager"

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(From yocto-docs rev: c402ebcb51b6400d79c62ff44aeae57db982565e)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2019-10-12 06:46:35 -07:00
committed by Richard Purdie
parent ea55d874e8
commit b22c6f673f
1 changed files with 41 additions and 0 deletions
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41
documentation/dev-manual/dev-manual-common-tasks.xml
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@@ -10819,6 +10819,47 @@
features that are used by many distributions.
</para>
<para>
By default, the Yocto Project uses SysVinit as the initialization
manager.
However, support also exists for systemd,
which is a full replacement for init with
parallel starting of services, reduced shell overhead and other
features that are used by many distributions.
</para>
<para>
Within the system, SysVinit treats system components as services.
These services are maintained as shell scripts stored in the
<filename>/etc/init.d/</filename> directory.
Services organize into different run levels.
This organization is maintained by putting links to the services
in the <filename>/etc/rcN.d/</filename> directories, where
<replaceable>N/</replaceable> is one of the following options:
"S", "0", "1", "2", "3", "4", "5", or "6".
<note>
Each runlevel has a dependency on the previous runlevel.
This dependency allows the services to work properly.
</note>
</para>
<para>
In comparison, systemd treats components as units.
Using units is a broader concept as compared to using a service.
A unit includes several different types of entities.
Service is one of the types of entities.
The runlevel concept in SysVinit corresponds to the concept of a
target in systemd, where target is also a type of supported unit.
</para>
<para>
In a SysVinit-based system, services load sequentially (i.e. one
by one) during and parallelization is not supported.
With systemd, services start in parallel.
Needless to say, the method can have an impact on system startup
performance.
</para>
<para>
If you want to use SysVinit, you do
not have to do anything.