| 講init進程的啟動過程從/etc/inittab出發。 內核啟動init進程時已經打開/dev/console設備作為控制臺，一般情況下Busybox init程序就使用/dev/console， 如果內核啟動init進程的同時設置了環境變量CONSOLE或console，則使用環境變量所指定的設備。 1、/etc/inittab文件的相關文檔和示例代碼都在Busybox 的examples/inittab文件中。 vi examples/inittab 內容如下(紅色字為格式重要部分)： # /etc/inittab init(8) configuration for BusyBox
#
# Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
#
#
# Note, BusyBox init doesn't support runlevels. The runlevels field is
# completely ignored by BusyBox init. If you want runlevels, use sysvinit.
#
#
# Format for each entry: <id>:<runlevels>:<action>:<process>
#
# <id>: WARNING: This field has a non-traditional meaning for BusyBox init!
#
# The id field is used by BusyBox init to specify the controlling tty for
# the specified process to run on. The contents of this field are
# appended to "/dev/" and used as-is. There is no need for this field to
# be unique, although if it isn't you may have strange results. If this
# field is left blank, it is completely ignored. Also note that if
# BusyBox detects that a serial console is in use, then all entries
# containing non-empty id fields will be ignored. BusyBox init does
# nothing with utmp. We don't need no stinkin' utmp.
<runlevels>: The runlevels field is completely ignored.
#
# <action>: Valid actions include: sysinit, respawn, askfirst, wait, once,
# restart, ctrlaltdel, and shutdown.
#
# Note: askfirst acts just like respawn, but before running the specified
# process it displays the line "Please press Enter to activate this
# console." and then waits for the user to press enter before starting
# the specified process.
#
# Note: unrecognised actions (like initdefault) will cause init to emit
# an error message, and then go along with its business.
#
# <process>: Specifies the process to be executed and it's command line.
#
# Note: BusyBox init works just fine without an inittab. If no inittab is
# found, it has the following default behavior:
# ::sysinit:/etc/init.d/rcS
# ::askfirst:/bin/sh
# ::ctrlaltdel:/sbin/reboot
# ::shutdown:/sbin/swapoff -a
# ::shutdown:/bin/umount -a -r
# ::restart:/sbin/init
#
# if it detects that /dev/console is _not_ a serial console, it will
# also run:
# tty2::askfirst:/bin/sh
# tty3::askfirst:/bin/sh
# tty4::askfirst:/bin/sh
#
# Boot-time system configuration/initialization script.
# This is run first except when booting in single-user mode.
#
::sysinit:/etc/init.d/rcS
# /bin/sh invocations on selected ttys
#
# Note below that we prefix the shell commands with a "-" to indicate to the
# shell that it is supposed to be a login shell. Normally this is handled by
# login, but since we are bypassing login in this case, BusyBox lets you do
# this yourself...
#
# Start an "askfirst" shell on the console (whatever that may be)
::askfirst:-/bin/sh
# Start an "askfirst" shell on /dev/tty2-4
tty2::askfirst:-/bin/sh
tty3::askfirst:-/bin/sh
tty4::askfirst:-/bin/sh
# /sbin/getty invocations for selected ttys
tty4::respawn:/sbin/getty 38400 tty5
tty5::respawn:/sbin/getty 38400 tty6
# Example of how to put a getty on a serial line (for a terminal)
#::respawn:/sbin/getty -L ttyS0 9600 vt100
#::respawn:/sbin/getty -L ttyS1 9600 vt100
#
# Example how to put a getty on a modem line.
#::respawn:/sbin/getty 57600 ttyS2
# Stuff to do when restarting the init process
::restart:/sbin/init
# Stuff to do before rebooting
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
::shutdown:/sbin/swapoff -a
2、仿照Busybox 的examples/inittab 文件，創建一個inittab文件，內容如下： #/etc/inittab #init進程啟動的第一個子進程，它是一個腳本，可以在里面指定用戶想執行的操作 #比較掛接其他文件系統、配置網絡等 ::sysinit:/etc/init.d/rcS #啟動shell，以/dev/ttySAC0作為控制臺 ttySAC0::askfirst:-/bin/sh #按下Ctrl＋Alt＋Del之后執行的程序，不過在串口控制臺中無法輸入Ctrl＋Alt＋Del組合鍵 ::ctrlaltdel:/sbin/reboot #重啟、關機前執行的程序 ::shutdown:/bin/umount -a -r | 
