Complete Yocto mirror with license table for TQMa6UL (2038-compliance)
- 264 license table entries with exact download URLs (224/264 resolved) - Complete sources/ directory with all BitBake recipes - Build configuration: tqma6ul-multi-mba6ulx, spaetzle (musl) - Full traceability for Softwarefreigabeantrag - GCC 13.4.0, Linux 6.6.102, U-Boot 2023.04, musl 1.2.4 - License distribution: GPL-2.0 (24), MIT (23), GPL-2.0+ (18), BSD-3 (16)
This commit is contained in:
Siggi (OpenClaw Agent)
162
sources/poky/documentation/dev-manual/init-manager.rst
Normal file
162
sources/poky/documentation/dev-manual/init-manager.rst
Normal file
@@ -0,0 +1,162 @@
|
||||
.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
|
||||
|
||||
.. _init-manager:
|
||||
|
||||
Selecting an Initialization Manager
|
||||
***********************************
|
||||
|
||||
By default, the Yocto Project uses :wikipedia:`SysVinit <Init#SysV-style>` as
|
||||
the initialization manager. There is also support for BusyBox init, a simpler
|
||||
implementation, as well as support for :wikipedia:`systemd <Systemd>`, which
|
||||
is a full replacement for init with parallel starting of services, reduced
|
||||
shell overhead, increased security and resource limits for services, and other
|
||||
features that are used by many distributions.
|
||||
|
||||
Within the system, SysVinit and BusyBox init treat system components as
|
||||
services. These services are maintained as shell scripts stored in the
|
||||
``/etc/init.d/`` directory.
|
||||
|
||||
SysVinit is more elaborate than BusyBox init and organizes services in
|
||||
different run levels. This organization is maintained by putting links
|
||||
to the services in the ``/etc/rcN.d/`` directories, where `N/` 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.
|
||||
|
||||
Both SysVinit and BusyBox init are configured through the ``/etc/inittab``
|
||||
file, with a very similar syntax, though of course BusyBox init features
|
||||
are more limited.
|
||||
|
||||
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.
|
||||
|
||||
In systems with SysVinit or BusyBox init, services load sequentially (i.e. one
|
||||
by one) during init and parallelization is not supported. With systemd, services
|
||||
start in parallel. This method can have an impact on the startup performance
|
||||
of a given service, though systemd will also provide more services by default,
|
||||
therefore increasing the total system boot time. systemd also substantially
|
||||
increases system size because of its multiple components and the extra
|
||||
dependencies it pulls.
|
||||
|
||||
On the contrary, BusyBox init is the simplest and the lightest solution and
|
||||
also comes with BusyBox mdev as device manager, a lighter replacement to
|
||||
:wikipedia:`udev <Udev>`, which SysVinit and systemd both use.
|
||||
|
||||
The ":ref:`device-manager`" chapter has more details about device managers.
|
||||
|
||||
Using SysVinit with udev
|
||||
=========================
|
||||
|
||||
SysVinit with the udev device manager corresponds to the
|
||||
default setting in Poky. This corresponds to setting::
|
||||
|
||||
INIT_MANAGER = "sysvinit"
|
||||
|
||||
Using BusyBox init with BusyBox mdev
|
||||
====================================
|
||||
|
||||
BusyBox init with BusyBox mdev is the simplest and lightest solution
|
||||
for small root filesystems. All you need is BusyBox, which most systems
|
||||
have anyway::
|
||||
|
||||
INIT_MANAGER = "mdev-busybox"
|
||||
|
||||
Using systemd
|
||||
=============
|
||||
|
||||
The last option is to use systemd together with the udev device
|
||||
manager. This is the most powerful and versatile solution, especially
|
||||
for more complex systems::
|
||||
|
||||
INIT_MANAGER = "systemd"
|
||||
|
||||
This will enable systemd and remove sysvinit components from the image.
|
||||
See :yocto_git:`meta/conf/distro/include/init-manager-systemd.inc
|
||||
</poky/tree/meta/conf/distro/include/init-manager-systemd.inc>` for exact
|
||||
details on what this does.
|
||||
|
||||
Controling systemd from the target command line
|
||||
-----------------------------------------------
|
||||
|
||||
Here is a quick reference for controling systemd from the command line on the
|
||||
target. Instead of opening and sometimes modifying files, most interaction
|
||||
happens through the ``systemctl`` and ``journalctl`` commands:
|
||||
|
||||
- ``systemctl status``: show the status of all services
|
||||
- ``systemctl status <service>``: show the status of one service
|
||||
- ``systemctl [start|stop] <service>``: start or stop a service
|
||||
- ``systemctl [enable|disable] <service>``: enable or disable a service at boot time
|
||||
- ``systemctl list-units``: list all available units
|
||||
- ``journalctl -a``: show all logs for all services
|
||||
- ``journalctl -f``: show only the last log entries, and keep printing updates as they arrive
|
||||
- ``journalctl -u``: show only logs from a particular service
|
||||
|
||||
Using systemd-journald without a traditional syslog daemon
|
||||
----------------------------------------------------------
|
||||
|
||||
Counter-intuitively, ``systemd-journald`` is not a syslog runtime or provider,
|
||||
and the proper way to use ``systemd-journald`` as your sole logging mechanism is to
|
||||
effectively disable syslog entirely by setting these variables in your distribution
|
||||
configuration file::
|
||||
|
||||
VIRTUAL-RUNTIME_syslog = ""
|
||||
VIRTUAL-RUNTIME_base-utils-syslog = ""
|
||||
|
||||
Doing so will prevent ``rsyslog`` / ``busybox-syslog`` from being pulled in by
|
||||
default, leaving only ``systemd-journald``.
|
||||
|
||||
Summary
|
||||
-------
|
||||
|
||||
The Yocto Project supports three different initialization managers, offering
|
||||
increasing levels of complexity and functionality:
|
||||
|
||||
.. list-table::
|
||||
:widths: 40 20 20 20
|
||||
:header-rows: 1
|
||||
|
||||
* -
|
||||
- BusyBox init
|
||||
- SysVinit
|
||||
- systemd
|
||||
* - Size
|
||||
- Small
|
||||
- Small
|
||||
- Big [#footnote-systemd-size]_
|
||||
* - Complexity
|
||||
- Small
|
||||
- Medium
|
||||
- High
|
||||
* - Support for boot profiles
|
||||
- No
|
||||
- Yes ("runlevels")
|
||||
- Yes ("targets")
|
||||
* - Services defined as
|
||||
- Shell scripts
|
||||
- Shell scripts
|
||||
- Description files
|
||||
* - Starting services in parallel
|
||||
- No
|
||||
- No
|
||||
- Yes
|
||||
* - Setting service resource limits
|
||||
- No
|
||||
- No
|
||||
- Yes
|
||||
* - Support service isolation
|
||||
- No
|
||||
- No
|
||||
- Yes
|
||||
* - Integrated logging
|
||||
- No
|
||||
- No
|
||||
- Yes
|
||||
|
||||
.. [#footnote-systemd-size] Using systemd increases the ``core-image-minimal``
|
||||
image size by 160\% for ``qemux86-64`` on Mickledore (4.2), compared to SysVinit.
|
||||
Reference in New Issue
Block a user