mirror of
https://git.linuxfromscratch.org/lfs.git
synced 2026-09-12 02:54:09 -04:00
b67bea305c
This doesn't replace Systemd or SysVinit rendering options. When going through, I discovered some issues with the main OpenRC branch which I fixed along the way. There is a UEFI issue I'm embarresed I didn't notice yet, which was a /boot/efi entry in the /etc/fstab section. So I will resolve that soon here.
135 lines
4.5 KiB
XML
135 lines
4.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-config-introduction" revision="openrc,sysv">
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<?dbhtml filename="introduction.html"?>
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<title>Introduction</title>
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<para>Booting a Linux system involves several tasks. The process must
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mount both virtual and real file systems, initialize devices,
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check file systems for integrity, mount and activate any swap partitions or files, set
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the system clock, bring up networking, start any daemons required by the
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system, and accomplish any other custom tasks specified by the user. This
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process must be organized to ensure the tasks are performed in the correct
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order and executed as quickly as possible.</para>
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<sect2 revision='openrc' id='openrc-desc'>
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<title>OpenRC</title>
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<para>OpenRC combines the methodology of both SysVinit and Systemd.
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OpenRC has the concept of services with dependency information, yet it uses
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a run level scheme which is similar to SysVinit. OpenRC, like SysVinit and
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Systemd, uses <command>init</command> and starts up every process and
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daemon as required. While you can choose which run level you want to be on,
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<literal>default</literal> has the most services and is the default. For
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information on run levels, see <xref linkend="ch-config-usage"/>.</para>
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</sect2>
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<sect2 revision='sysv' id='sysv-desc'>
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<title>System V</title>
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<para>System V is the classic boot process that has been used in Unix and
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Unix-like systems such as Linux since about 1983. It consists of a small
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program, <command>init</command>, that sets up basic processes such as
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<command>login</command> (via getty) and runs a script. This script,
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usually named <command>rc</command>, controls the execution of a set of
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additional scripts that perform the tasks required to initialize the
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system.</para>
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<para>The <command>init</command> program is controlled by the
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<filename>/etc/inittab</filename> file and is organized into run levels that
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can be chosen by the user. In LFS, they are used as follows:</para>
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<literallayout>0 — halt
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1 — Single user mode
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2 — User definable
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3 — Full multiuser mode
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4 — User definable
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5 — Full multiuser mode with display manager
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6 — reboot</literallayout>
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<para>The usual default run level is 3 or 5.</para>
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</sect2>
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<sect2>
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<title>Advantages</title>
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<itemizedlist>
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<listitem>
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<para>Established, well understood system.</para>
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</listitem>
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<listitem>
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<para>Easy to customize.</para>
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</listitem>
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<listitem revision="openrc">
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<para>Well supported and backed by major Linux distributions.</para>
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</listitem>
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<listitem revision="openrc">
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<para>Parallelized.</para>
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</listitem>
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<listitem revision="openrc">
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<para>Cgroups support.</para>
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</listitem>
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</itemizedlist>
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</sect2>
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<sect2>
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<title>Disadvantages</title>
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<itemizedlist>
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<listitem revision="openrc">
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<para>It is not as convenient as Systemd.</para>
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</listitem>
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<listitem revision="openrc">
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<para>It does not provide the amount of tooling Systemd does.</para>
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</listitem>
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<listitem revision="openrc">
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<para>Certain features that projects depend on that only exist in
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Systemd may take a while before seeing parity in OpenRC.</para>
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</listitem>
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<listitem revision="sysv">
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<para>May be slower to boot. A medium speed base LFS system
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takes 8-12 seconds where the boot time is measured from the
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first kernel message to the login prompt. Network
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connectivity is typically established about 2 seconds
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after the login prompt.</para>
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</listitem>
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<listitem revision="sysv">
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<para>Serial processing of boot tasks. This is related to the previous
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point. A delay in any process, such as a file system check, will
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delay the entire boot process.</para>
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</listitem>
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<listitem revision="sysv">
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<para>Does not directly support advanced features like
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control groups (cgroups) and per-user fair share scheduling.</para>
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</listitem>
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<listitem revision="sysv">
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<para>Adding scripts requires manual, static sequencing decisions.</para>
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</listitem>
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</itemizedlist>
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</sect2>
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</sect1>
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