一、启动级别
1、查看linux 系统默认启动级别
cat /etc/inittab
id:3:initdefault: ##可以看出默认为三
cat /etc/inittab
id:3:initdefault: ##可以看出默认为三
2、查看某一服务在各个启动级别上是否启动
[root@localhost ~]# chkconfig --list nfs
nfs 0:off 1:off 2:off 3:off 4:off 5:off 6:off
[root@localhost ~]# chkconfig --list nfs
nfs 0:off 1:off 2:off 3:off 4:off 5:off 6:off
3、在Linux中有7种启动级别
分别为：
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
各个运行级的详细解释：
0 为停机，机器关闭。
1 为单用户模式，就像Win9x下的安全模式类似。
2 为多用户模式，但是没有NFS支持。
3 为完整的多用户模式，是标准的运行级。
4 一般不用，在一些特殊情况下可以用它来做一些事情。例如在笔记本电脑的电池用尽时，可以切换到这个模式来做一些设置。
5 就是X11，进到X Window系统了。
6 为重启，运行init 6机器就会重启。
分别为：
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
各个运行级的详细解释：
0 为停机，机器关闭。
1 为单用户模式，就像Win9x下的安全模式类似。
2 为多用户模式，但是没有NFS支持。
3 为完整的多用户模式，是标准的运行级。
4 一般不用，在一些特殊情况下可以用它来做一些事情。例如在笔记本电脑的电池用尽时，可以切换到这个模式来做一些设置。
5 就是X11，进到X Window系统了。
6 为重启，运行init 6机器就会重启。
0和6一般不用；
二、 chkconfig
说明 ：linux 的所有服务都在 /etc/init.d/ 下， 但是 /etc/init.d 是 链接的 /etc/rc.d/init.d
同样 /etc/rc[0-6].d 都是连接的相应的 /etc/rc.d/rc[0-6].d ，不同启动级别的 rc[0-6].d 中的服务都是 链接的 /etc/init.d 下的相应服务
同样 /etc/rc[0-6].d 都是连接的相应的 /etc/rc.d/rc[0-6].d ，不同启动级别的 rc[0-6].d 中的服务都是 链接的 /etc/init.d 下的相应服务
1、chkconfig命令主要用来更新（启动或停止）和查询系统服务的运行级信息。谨记chkconfig不是立即自动禁止或激活一个服务，它只是简单的改变了符号连接。
语法：
chkconfig --list [name]
chkconfig --add name
chkconfig --del name
chkconfig [--level levels] name <on|off|reset>
chkconfig [--level levels] name
chkconfig 没有参数运行时，显示用法。如果加上服务名，那么就检查这个服务是否在当前运行级启动。如果是，返回true，否则返回false。如果在服务名后面指定了on，off或者reset，那么chkconfi 会改变指定服务的启动信息。on和off分别指服务被启动和停止，reset指重置服务的启动信息，无论有问题的初始化脚本指定了什么。on和off开关，系统默认只对运行级2，3，4，5有效，但是reset可以对所有运行级有效。
--level选项可以指定要查看的运行级而不一定是当前运行级。
需要说明的是，对于每个运行级，只能有一个启动脚本或者停止脚本。当切换运行级时，init不会重新启动已经启动的服务，也不会再次去停止已经停止的服务。
--level选项可以指定要查看的运行级而不一定是当前运行级。
需要说明的是，对于每个运行级，只能有一个启动脚本或者停止脚本。当切换运行级时，init不会重新启动已经启动的服务，也不会再次去停止已经停止的服务。
2、 chkconfig --list ：显示所有运行级系统服务的运行状态信息（on或off）。如果指定了name，那么只显示指定的服务在不同运行级的状态。
chkconfig --add name：增加一项新的服务。chkconfig确保每个运行级有一项启动(S)或者杀死(K)入口。如有缺少，则会从缺省的init脚本自动建立。
chkconfig --del name：删除服务，并把相关符号连接从/etc/rc[0-6].d删除。
chkconfig [--level levels] name <on|off|reset>：设置某一服务在指定的运行级是被启动，停止还是重置。例如，要在3，4，5运行级停止nfs服务，则命令如下：
chkconfig --level 345 nfs off
chkconfig --level 345 nfs off
3、举例sendmail：
1）cat /etc/inittab
id:3:initdefault:
id:3:initdefault:
2）chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off
查看连接 ：
ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 K30sendmail -> ../init.d/sendmail
ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 K30sendmail -> ../init.d/sendmail
ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 K30sendmail -> ../init.d/sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off
查看连接 ：
ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 K30sendmail -> ../init.d/sendmail
ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 K30sendmail -> ../init.d/sendmail
ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 S80sendmail -> ../init.d/sendmail
ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 5 23:43 K30sendmail -> ../init.d/sendmail
3）chkconfig --del sendmail
[root@localhost init.d]# chkconfig --list sendmail
service sendmail supports chkconfig, but is not referenced in any runlevel (run 'chkconfig --add sendmail')
查看连接
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
[root@localhost init.d]# ---》 全为空
[root@localhost init.d]# chkconfig --list sendmail
service sendmail supports chkconfig, but is not referenced in any runlevel (run 'chkconfig --add sendmail')
查看连接
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
[root@localhost init.d]# ---》 全为空
4）
[root@localhost init.d]# chkconfig --add sendmail
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off
[root@localhost init.d]# chkconfig --add sendmail
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off
查看连接：
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail ----》 相应的服务连接又回来了
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail ----》 相应的服务连接又回来了
5）chkconfig sendmail off --》on和off分别指服务被启动和停止，reset指重置服务的启动信息，无论有问题的初始化脚本指定了什么。on和off开关，系统 默认只对运行级3，4，5有效，但是reset可以对所有运行级有效
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off
查看连接：
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail ---》全是 "K"
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:36 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail ---》全是 "K"
6)chkconfig sendmail on
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off
查看连接：
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail --》2，3，4，5 为“S” 其他为 K
[root@localhost init.d]# ll /etc/rc0.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc1.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc2.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc3.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc4.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc5.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:40 S80sendmail -> ../init.d/sendmail
[root@localhost init.d]# ll /etc/rc6.d/ |grep sendmail
lrwxrwxrwx 1 root root 18 Nov 10 23:33 K30sendmail -> ../init.d/sendmail --》2，3，4，5 为“S” 其他为 K
7）
chkconfig sendmail off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off
[root@localhost init.d]# chkconfig --level 3 sendmail on
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:on 4:off 5:off 6:off
[root@localhost init.d]# chkconfig --level 0 sendmail on
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:on 1:off 2:off 3:on 4:off 5:off 6:off --》 看来 得用level on 参数控制 0级别
chkconfig sendmail off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off
[root@localhost init.d]# chkconfig --level 3 sendmail on
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:on 4:off 5:off 6:off
[root@localhost init.d]# chkconfig --level 0 sendmail on
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:on 1:off 2:off 3:on 4:off 5:off 6:off --》 看来 得用level on 参数控制 0级别
[root@localhost init.d]# chkconfig sendmail off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:on 1:off 2:off 3:off 4:off 5:off 6:off --》 但是这样3 级别关了 0 级别没关掉
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:on 1:off 2:off 3:off 4:off 5:off 6:off --》 但是这样3 级别关了 0 级别没关掉
[root@localhost init.d]# chkconfig --level 0 sendmail off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off --》 0 级别关掉了 （经验证1，6级别 也是这样的和0级别一样 得用level控制）
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off --》 0 级别关掉了 （经验证1，6级别 也是这样的和0级别一样 得用level控制）
8）
[root@localhost init.d]# chkconfig sendmail off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off
[root@localhost init.d]# chkconfig sendmail reset
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off --》 reset指重置服务的启动信息 可以对所有运行级有效 （没太懂这个东西reset）
[root@localhost init.d]# chkconfig sendmail off
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:off 3:off 4:off 5:off 6:off
[root@localhost init.d]# chkconfig sendmail reset
[root@localhost init.d]# chkconfig --list sendmail
sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off --》 reset指重置服务的启动信息 可以对所有运行级有效 （没太懂这个东西reset）