1 -- Linux运行级
运行级就是操作系统当前正在运行的功能级别，根据运行级的不同加载不同的系统服务。
2 -- chkconfig命令
usage:
chkconfig -t|--terse [names] (shows the links)
chkconfig -e|--edit [names] (configure services)
chkconfig -s|--set [name state]... (configure services)
chkconfig -l|--list [--deps] [names] (shows the links)
chkconfig -c|--check name [state] (check state)
chkconfig -a|--add [names] (runs insserv)
chkconfig -d|--del [names] (runs insserv -r)
chkconfig -h|--help (print usage)
chkconfig -f|--force ... (call insserv with -f)
chkconfig [name] same as chkconfig -t
chkconfig name state... same as chkconfig -s name state