构建根文件系统(2)Busybox init 进程

讲init进程的启动过程从/etc/inittab出发。 内核启动init进程时已经打开/dev/console设备作为控制台，一般情况下Busybox init程序就使用/dev/console， 如果内核启动init进程的同时设置了环境变量CONSOLE或console，则使用环境变量所指定的设备。 1、/etc/inittab文件的相关文档和示例代码都在Busybox 的examples/inittab文件中。 vi examples/inittab 内容如下(红色字为格式重要部分)： # /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，创建一个inittab文件，内容如下： #/etc/inittab #init进程启动的第一个子进程，它是一个脚本，可以在里面指定用户想执行的操作 #比较挂接其他文件系统、配置网络等 ::sysinit:/etc/init.d/rcS #启动shell，以/dev/ttySAC0作为控制台 ttySAC0::askfirst:-/bin/sh #按下Ctrl＋Alt＋Del之后执行的程序，不过在串口控制台中无法输入Ctrl＋Alt＋Del组合键 ::ctrlaltdel:/sbin/reboot #重启、关机前执行的程序 ::shutdown:/bin/umount -a -r

转载于:https://www.cnblogs.com/huanghuang/archive/2011/09/19/2181417.html