[debian-reference] 17/45: update init and describe sysv-style init
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osamu pushed a commit to branch master
in repository debian-reference.
commit 6368ccfefd432b85a2c16ab727f7b46f92f081fd
Author: Osamu Aoki <osamu@debian.org>
Date: Mon Nov 4 03:39:44 2013 +0900
update init and describe sysv-style init
---
asciidoc/03_sysinit.txt | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/asciidoc/03_sysinit.txt b/asciidoc/03_sysinit.txt
index 534aab9..0f841d6 100644
--- a/asciidoc/03_sysinit.txt
+++ b/asciidoc/03_sysinit.txt
@@ -130,6 +130,16 @@ CAUTION: You need to use "`-n`" option for `mount` command when you are on the r
=== Stage 4: the normal Debian system
+The normal Debian system is the 4th stage of the boot process which is started by the mini-Debian system. The system kernel for the mini-Debian system continues to run in this environment. The root filesystem is switched from the one on the memory to the one on the real hard disk filesystem.
+
+The http://en.wikipedia.org/wiki/Init[init] program is executed as the first program with PID=1 to perform the main boot process of starting many programs. The default file path for the init program is "`/sbin/init`" but it can be changed by the kernel boot parameter as "`init=/path/to/init_program`".
+
+The default init program has been changing:
+
+- Debian before `squeeze` uses the simple http://en.wikipedia.org/wiki/UNIX_System_V[SysV]-style init.
+- Debian from `wheezy` improves the SysV-style init by ordering the boot sequence with LSB header and starting boot scripts in parallel.
+- Debian after `wheezy` may switch its init to the newer init system such as `upstart`, `systemd`, ...
+
.List of boot utilities for the Debian system
[grid="all"]
`-------------------`-------------`------------`-----------------------------------------------------------------------------
@@ -160,9 +170,11 @@ TIP: The `readahead-fedora` package can speed up starting of a system with decen
TIP: See https://wiki.debian.org/BootProcessSpeedup[Debian wiki: BootProcessSpeedup] for the latest tips to speed up the boot process.
-The normal Debian system is the 4th stage of the boot process which is started by the mini-Debian system. The system kernel for the mini-Debian system continues to run in this environment. The root filesystem is switched from the one on the memory to the one on the real hard disk filesystem.
+=== SysV-style init
-The "`/sbin/init`" program is executed as the first program and performs the main boot process. Debian normally uses the traditional sysvinit scheme with the `sysv-rc` package. See `init`(8), `inittab`(5), and "`/usr/share/doc/sysv-rc/README.runlevels.gz`" for the exact explanation. This main boot process essentially goes through the following.
+This section describes how the good old SysV-style init used to boot the system. Your Debian system does not function exactly as described here but it is quite educational to know this basics since the newer init system tends to offer equivalent functionalities.
+
+The SysV-style boot process essentially goes through the following.
1. The Debian system goes into **runlevel N** (none) to initialize the system by following the "`/etc/inittab`" description.
2. The Debian system goes into **runlevel S** to initialize the system under the single-user mode to complete hardware initialization etc.
@@ -172,6 +184,8 @@ The initial runlevel used for multi-user mode is specified with the "`init=`" ke
All actual script files executed by the init system are located in the directory "`/etc/init.d/`".
+See `init`(8), `inittab`(5), and "`/usr/share/doc/sysv-rc/README.runlevels.gz`" for the exact explanation.
+
==== The meaning of the runlevel
Each http://en.wikipedia.org/wiki/Runlevel[runlevel] uses a directory for its configuration and has specific meaning as the following.
@@ -327,7 +341,7 @@ error level value error level name meaning
==== The udev system
-For Linux kernel 2.6, http://en.wikipedia.org/wiki/Udev[the udev system] provides mechanism for the automatic hardware discovery and initialization (see `udev`(7)). Upon discovery of each device by the kernel, the udev system starts a user process which uses information from the http://en.wikipedia.org/wiki/Sysfs[sysfs] filesystem (see <<_procfs_and_sysfs>>), loads required kernel modules supporting it using the `modprobe`(8) program (see <<_the_kernel_module_initialization>>), and creat [...]
+For Linux kernel 2.6 and newer, http://en.wikipedia.org/wiki/Udev[the udev system] provides mechanism for the automatic hardware discovery and initialization (see `udev`(7)). Upon discovery of each device by the kernel, the udev system starts a user process which uses information from the http://en.wikipedia.org/wiki/Sysfs[sysfs] filesystem (see <<_procfs_and_sysfs>>), loads required kernel modules supporting it using the `modprobe`(8) program (see <<_the_kernel_module_initialization>>), [...]
TIP: If "`/lib/modules/<kernel-version>/modules.dep`" was not generated properly by `depmod`(8) for some reason, modules may not be loaded as expected by the udev system. Execute "`depmod -a`" to fix it.
--
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