linux sysvinit与upstart(2)
本文地址：http://blog.csdn.net/spch2008/article/details/9469775
有一个upstart的介绍，我觉得写的很清楚，值得一看。
这里采用的测试环境为ubuntu 12.04 server
Job：可以认为是一个服务或一个任务。可以通过配置文件来定义一个Job，如spch2008.conf，这样就定义了一个
名为spch2008的Job。该配置文件放置于/etc/init下。
Script：配置文件中写入相应的脚本，完成指定功能。
#脚本格式
script
# do some thing
if [ ... ]; then
...
fi
end script
pre-start script
# prepare environment
mkdir -p /var/run/foo
end script
Job States：状态迁移
| Current State |
Goal | |
|---|---|---|
| start | stop | |
| waiting | starting | n/a |
| starting | pre-start | stopping |
| pre-start | spawned | stopping |
| spawned | post-start | stopping |
| post-start | running | stopping |
| running | stopping | pre-stop or stopping [11] |
| pre-stop | running | stopping |
| stopping | killed | killed |
| killed | post-stop | post-stop |
| post-stop | starting | waiting |
假如当前状态处于waiting，执行start命令。首先由waiting转移到starting，然后starting==》pre-start==》spawned==》post-start==》running。
到达running状态，程序就运行起来了。
waiting : initial state. starting : job is about to start. pre-start : running pre-start section. spawned : about to run script or exec section. post-start : running post-start section. running : interim state set after post-start section processed denoting job is running pre-stop : running pre-stop section. stopping : interim state set after pre-stop section processed. killed : job is about to be stopped. post-stop : running post-stop section.从上述可以看出，pre-start状态对应于”pre-start script end script“代码段，即处于pre-start状态时，正在执行pre-start script代码段。
实例：通过一个实例观察状态迁移过程。
#spch2008.conf
script
mkdir -p /home/spch2008
chown root:root /home/spch2008
end script将上述代码保存为spch2008.conf，放置于/etc/init目录下。
执行：
root@nova-controller:/var/log# initctl log-priority debug
启动服务：
root@nova-controller:/var/log# status spch2008 spch2008 stop/waiting root@nova-controller:/var/log# start spch2008 spch2008 start/running, process 22805 root@nova-controller:/var/log#上述过程在/home下创建了spch2008文件夹。
打开/var/log/syslog 看一下状态迁移情况。
root@nova-controller:/var/log# cat syslog | grep init很清楚的显示了各个状态的迁移情况。
init: spch2008 goal changed from stop to start init: spch2008 state changed from waiting to starting init: event_new: Pending starting event init: Handling starting event init: event_finished: Finished starting event init: spch2008 state changed from starting to pre-start init: spch2008 state changed from pre-start to spawned init: spch2008 main process (22538) init: spch2008 state changed from spawned to post-start init: spch2008 state changed from post-start to running init: event_new: Pending started event init: Handling started event init: event_finished: Finished started event init: spch2008 main process (22538) exited normally init: spch2008 goal changed from start to stop init: spch2008 state changed from running to stopping init: event_new: Pending stopping event init: Handling stopping event init: event_finished: Finished stopping event init: spch2008 state changed from stopping to killed init: spch2008 state changed from killed to post-stop init: spch2008 state changed from post-stop to waiting init: event_new: Pending stopped event init: job_change_state: Destroyed inactive instance spch2008 init: Handling stopped event init: event_finished: Finished stopped event
那么如何让程序可以在开机的时候自动运行呢？可以在rc.local中，写入相应的命令。但upstart可以通过事件完成。
start on runlevel [2345]
stop on runlevel [016]
run level在上一篇linux sysvinit已经说明了，上述命令在level2,3,4,5情况下启动，在0,1,6情况下关闭。
参考：http://upstart.ubuntu.com/cookbook/