Linux system boot details (iii)

The previous section has the system Initramfs has started to complete, the system control to the real Rootfs/sbin/init, the following is the time/sbin/init work.

4/sbin/init

Initramfs init script, through the Switch_root command, after switching to the real root FS, the first program executed is the root FS under the/sbin/init,

4.1 switch_root

Swith_root newroot Init [arg]

eg

The INITRAMFS switch to the real rootfs command is Switch_root/sysroot/sbin/init

where Root fs is mounted in the/sysroot directory

4.2/sbin/init

/sbin/init: It is the first program executed by the system, that is, using PA auxf view, the PID 1 program is it, it can be understood as the parent process of all processes of the system.

From the Rpm-qf/sbin/init, see upstart [6] for a detailed description of the/sbin/init program in the system from Upstart,upstart.

The traditional operating system/sbin/init is managed by System V Init, and upstart was originally developed for Ubuntu systems and is now used by more and more Linux systems. For the differences between system Vinit and upstart, refer to document [7].

/sbin/init The main process:

1, the implementation of/etc/rc.sysinit.

2. Execute/ETC/RC,RC script According to the incoming RunLevel, select Run script under the corresponding directory.

3, the implementation of/etc/rc.local

4.3 rc.sysinit

Roughly complete the following types of tasks:

1, File system mount (via grub incoming parameters, and configuration file, mount/repair file system).

2, module loading (through Udev rules, loading modules, such as network cards, user-defined rules, etc.).

3, SELinux related (not understood).

The following two links also have a few notes:

Http://linux.chinaunix.net/techdoc/beginner/2009/01/21/1059280.shtm

Http://www.cnblogs.com/image-eye/archive/2011/10/21/2220344.html

4.4 rc*.d

All service script directories, scripts of different levels corresponding to different directories are executed, which are no longer described in detail.

# Default RunLevel. The runlevels used is:

# 0-halt (do not set Initdefault to this)

# 1-single User mode

# 2-multiuser, without NFS (the same as 3, if you don't have networking)

# 3-full Multiuser mode

# 4-unused

# 5-x11

# 6-reboot (do not set Initdefault to this)

Linux system boot details (iii)