Runlevel笔记

简介

运行级别（Runlevel）指的是Unix或者Linux等类Unix操作系统下不同的运行模式。运行级别通常分为 7 等，分别是从 0 到 6 ，但如果必要的话也可以更多。

例如在大多数Linux操作系统下一共有如下7个典型的运行级别：

• 0 停机，关机
• 1 单用户，无网络连接，不运行守护进程，不允许非超级用户登录
• 2 多用户，无网络连接，不运行守护进程
• 3 多用户，正常启动系统
• 4 用户自定义
• 5 多用户，带图形界面
• 6 重启

/etc/init.d 和 /etc/rc*.d 那些事

1. /etc/rc*.d ----> The scripts are all symbolic links whose targets are located in /etc/init.d/ 

2. /etc/rc0.d ---->

Generally it is not necessary to alter the scripts in this directory.

Their purpose is to stop all services and to make the system ready

for shutdown.

3. /etc/rc1.d ----->

Generally it is not necessary to alter the scripts in this directory.

Their purpose is to stop all services and thus to put the system in

single-user mode.

4. /etc/rc2/3/4/5.d ----->

To disable a service in this runlevel, rename its script in this

directory so that the new name begins with a 'K' and a two-digit number, and run 'update-rc.d script defaults' to reorder the scripts according to dependencies.

A warning about the current runlevels being enabled not matching the LSB header in the init.d script will be printed.

To re-enable the service, rename the script back to its original name beginning with 'S' and run update-rc.d again.

5. /etc/rc6.d ----->

Generally it is not necessary to alter the scripts in this directory.

Their purpose is to stop all services and to make the system ready for reboot.

6. /etc/rcS.d ----->

The scripts in this directory whose names begin with an 'S' are

executed once when booting the system, even when booting directly into single user mode.

To disable a script in this directory, rename it so that it begins with a 'K' and run 'update-rc.d script defaults' to update the order using the script dependencies.