一系统运行级别文件

文件路径：/etc/inittab

文件作用说明：定义系统启动后，自动开启哪些软件程序系统

runlevel 查看当前运行级别

centos6系统运行级别: 7个级别
 
   0   -- 系统关机级别    init 0
   1   -- 系统单用户级别

用于破解系统密码root，救援恢复系统数据，没有网络服务
                      
   2   -- 系统多用户级别  没有网络多用户级别 
   3   -- 系统多用户级别  拥有网络多用户级别，生产中使用最多  
   4   -- 未使用级别
   5   -- 系统图形化级别  
   6   -- 系统重启级别    init 6

（一）查看当前运行级别

[root@centos61 ~]# cat  /etc/redhat-release

CentOS release 6.8 (Final)

[root@centos61 ~]# runlevel

N 
[root@centos71 ~]# cat  /etc/redhat-release

CentOS Linux release 7.6. (Core)

[root@centos71 ~]# runlevel

N

（二）centos6设置系统级别

临时设置：init   级别数字

[root@centos61 ~]# cat  /etc/inittab

# inittab is only used by upstart for the default runlevel.

#

# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.

#

# System initialization is started by /etc/init/rcS.conf

#

# Individual runlevels are started by /etc/init/rc.conf

#

# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf

#

# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,

# with configuration in /etc/sysconfig/init.

#

# For information on how to write upstart event handlers, or how

# upstart works, see init(), init(), and initctl().

#

# Default runlevel. The runlevels used are:

#    - halt (Do NOT set initdefault to this)

#    - Single user mode

#    - Multiuser, without NFS (The same as , if you do not have networking)

#    - Full multiuser mode

#    - unused

#    - X11

#    - reboot (Do NOT set initdefault to this)

#

id::initdefault:

此时断开远程连接

[root@centos61 ~]# init

[root@centos61 ~]#

Connection closed by foreign host.

Disconnected from remote host(centos61) at ::.

Type `help' to learn how to use Xshell prompt.

[c:\~]$

永久设置

对配置文件/etc/inittab修改

可以使用小工具进行修改，比如sed,awk，强化练习

[root@centos61 ~]# sed  -i   s/::/::/g  /etc/inittab

[root@centos61 ~]# tail  -   /etc/inittab

id::initdefault:
[root@centos61 ~]# runlevel

S

[root@centos61 ~]# reboot 

Broadcast message from root@centos61.huawei.com

    (/dev/pts/) at : ...

The system is going down for reboot NOW!

[root@centos61 ~]#

Connection closed by foreign host.

Disconnected from remote host(centos6-) at ::.

Type `help' to learn how to use Xshell prompt.

注意还要执行init  3才可以的

[root@centos61 ~]# runlevel

S

（三）centos7设置系统级别

和centos6有区别，使用target模式

[root@centos7 ~]# ll  /usr/lib/systemd/system/runlevel*target

lrwxrwxrwx. 1 root root 15 Nov 26 17:33 /usr/lib/systemd/system/runlevel0.target -> poweroff.target

lrwxrwxrwx. 1 root root 13 Nov 26 17:33 /usr/lib/systemd/system/runlevel1.target -> rescue.target

lrwxrwxrwx. 1 root root 17 Nov 26 17:33 /usr/lib/systemd/system/runlevel2.target -> multi-user.target

lrwxrwxrwx. 1 root root 17 Nov 26 17:33 /usr/lib/systemd/system/runlevel3.target -> multi-user.target

lrwxrwxrwx. 1 root root 17 Nov 26 17:33 /usr/lib/systemd/system/runlevel4.target -> multi-user.target

lrwxrwxrwx. 1 root root 16 Nov 26 17:33 /usr/lib/systemd/system/runlevel5.target -> graphical.target

lrwxrwxrwx. 1 root root 13 Nov 26 17:33 /usr/lib/systemd/system/runlevel6.target -> reboot.target

[root@centos7 ~]# runlevel

N 
[root@centos71 ~]# ll   /usr/lib/systemd/system/multi-user.target

-rw-r--r--.  root root  Oct    /usr/lib/systemd/system/multi-user.target

[root@centos71 ~]# ll   /usr/lib/systemd/system/rescue.target

-rw-r--r--.  root root  Oct    /usr/lib/systemd/system/rescue.target

[root@centos71 ~]# cat  /usr/lib/systemd/system/multi-user.target

#  This file is part of systemd.

#

#  systemd is free software; you can redistribute it and/or modify it

#  under the terms of the GNU Lesser General Public License as published by

#  the Free Software Foundation; either version 2.1 of the License, or

#  (at your option) any later version.

[Unit]

Description=Multi-User System

Documentation=man:systemd.special()

Requires=basic.target

Conflicts=rescue.service rescue.target

After=basic.target rescue.service rescue.target

AllowIsolate=yes


[root@centos71 ~]# cat  /usr/lib/systemd/system/rescue.target

#  This file is part of systemd.

#

#  systemd is free software; you can redistribute it and/or modify it

#  under the terms of the GNU Lesser General Public License as published by

#  the Free Software Foundation; either version 2.1 of the License, or

#  (at your option) any later version.

[Unit]

Description=Rescue Mode

Documentation=man:systemd.special()

Requires=sysinit.target rescue.service

After=sysinit.target rescue.service

AllowIsolate=yes

[Install]

Alias=kbrequest.target
   
 
临时设置:   init 级别数字
 
 
 
 
 
 

永久设置

 
在6版本的默认配置文件写明了
[root@centos71 ~]# cat  /etc/inittab

# inittab is no longer used when using systemd.

#

# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.

#

# Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target

#

# systemd uses 'targets' instead of runlevels. By default, there are two main targets:

#

# multi-user.target: analogous to runlevel

# graphical.target: analogous to runlevel

#

# To view current default target, run:

# systemctl get-default

#

# To set a default target, run:

# systemctl set-default TARGET.target
 
 
 
  
 
 
 
 

 
输入系统设置的口令即可
 
 
 
 

 
 
 
 
实现远程连接，切换级别
 
 
 
 

 
 
 
 
 
 
 
 
 

二系统登录前后提示文件

 
 

（一）登录系统前显示提示信息

文件路径: /etc/issue     /etc/issue.net
   
[root@centos71 ~]# ll  /etc/issue*

-rw-r--r--.  root root  Nov    /etc/issue

-rw-r--r--.  root root  Nov    /etc/issue.net

[root@centos71 ~]# cat  /etc/issue*

\S

Kernel \r on an \m

\S

Kernel \r on an \m

[root@centos71 ~]# cat  /etc/issue

\S

Kernel \r on an \m

[root@centos71 ~]# cat  /etc/issue.net

\S

Kernel \r on an \m

[root@centos71 ~]#
文件内容没有多大区别
[root@centos71 ~]# diff   /etc/issue*

3d2

<

[root@centos71 ~]# wc   /etc/issue.net

     /etc/issue.net

[root@centos71 ~]# wc   /etc/issue

     /etc/issue
 
 
 
 
 
 
 

（二）登录系统后显示提示信息

文件路径: /etc/motd
 默认没有内容，可以添加有意义的
 
[root@centos61 ~]# ll  /etc/motd

-rw-r--r--.  root root  Jan    /etc/motd
 
 
[root@centos71 ~]# cat  /etc/motd

                              (@@) (  ) (@)  ( )  @@    ()    @     O     @     O      @

                                 (   )

                             (@@@@)

                          (    )

                        (@@@)

                    ====        ________                ___________

                _D _|  |_______/        \__I_I_____===__|_________|

                 |(_)---  |   H\________/ |   |        =|___ ___|      _________________

                 /     |  |   H  |  |     |   |         ||_| |_||     _|                \_____A

                |      |  |   H  |__--------------------| [___] |   =|                        |

                | ________|___H__/__|_____/[][]~\_______|       |   -|                        |

                |/ |   |-----------I_____I [][] []  D   |=======|____|________________________|_

              __/ =| o |=-~~\  /~~\  /~~\  /~~\ ____Y___________|__|__________________________|_

               |/-=|___|=O=====O=====O=====O   |_____/~\___/          |_D__D__D_|  |_D__D__D_|

                \_/      \__/  \__/  \__/  \__/      \_/               \_/   \_/    \_/   \_/
 
 
 
[root@centos71 ~]# ll  /etc/motd

-rw-r--r--.  root root  Dec   : /etc/motd
 
 
 
 
 
 
 
 
 
 
 
 

三系统主机名配置文件

文件路径信息：/etc/hostname
文件作用说明：修改主机名称
 
 
PS：企业需求，统计主机信息==资产管理
PS可以理解为多说一句，plus  say
主机信息包括主机名称、主机网络地址、主机品牌型号、主机CPU、主机内存、主机存储信息
主机名称: 区域-机房-机柜号码-机器编号 BJ - pbs-010203  - 01

 
 
 
 
 
 

（一）centos6/7系统主机名称临时修改

hostname

[root@centos61 ~]# hostname

centos61.huawei.com

[root@centos61 ~]# hostname  centos6.com

[root@centos61 ~]# exit

logout

Connection closed by foreign host.

Disconnected from remote host(centos6-) at ::.

Type `help' to learn how to use Xshell prompt.

[c:\~]$ 

Connecting to 10.0.0.61:...

Connection established.

To escape to local shell, press Ctrl+Alt+].

Last login: Thu Dec   ::  from 10.0.0.1

[root@centos6 ~]# hostname

centos6.com

文件内容没有变化

[root@centos6 ~]# cat /etc/sysconfig/network

NETWORKING=yes

HOSTNAME=centos61.huawei.com
centos7的方法一样

[root@centos7 ~]# hostname   centos7.jd.com

[root@centos7 ~]# exit

logout

Connection closed by foreign host.

Disconnected from remote host(centos7-1) at 09:58:58.

Type `help' to learn how to use Xshell prompt.

[c:\~]$ ssh  10.0.0.72

Connecting to 10.0.0.200:22...

Connection established.

To escape to local shell, press Ctrl+Alt+].

WARNING! The remote SSH server rejected X11 forwarding request.

Last login: Wed Dec  4 08:27:57 2019 from 10.0.0.1

[root@centos7 ~]# hostname

centos7.jd.com

[root@centos7 ~]# cat  /etc/hostname

centos7.com
   
 
 
 
 
 
 

（二）centos6系统主机名称永久修改

注意修改之后要重启，注销没用

[root@centos6 ~]# hostname

centos6.com

[root@centos6 ~]# cat /etc/sysconfig/network

NETWORKING=yes

HOSTNAME=centos61.com

[root@centos6 ~]# exit

logout

Connection closed by foreign host.

Disconnected from remote host(centos6-) at ::.

Type `help' to learn how to use Xshell prompt.

[c:\~]$ 

Connecting to 10.0.0.61:...

Connection established.

To escape to local shell, press Ctrl+Alt+].

Last login: Thu Dec   ::  from 10.0.0.1

[root@centos6 ~]# hostname

centos6.com

重启之后变成了centos61

[root@centos6 ~]# hostname

centos6.com

[root@centos6 ~]# reboot 

Broadcast message from root@centos6.com

    (/dev/pts/) at : ...

The system is going down for reboot NOW!

[root@centos6 ~]#

Connection closed by foreign host.

Disconnected from remote host(centos6-) at ::.

Type `help' to learn how to use Xshell prompt.

[c:\~]$ 

Connecting to 10.0.0.61:...

Connection established.

To escape to local shell, press Ctrl+Alt+].

Last login: Thu Dec   ::  from 10.0.0.1

[root@centos61 ~]# hostname

centos61.com

[root@centos61 ~]# cat /etc/sysconfig/network

NETWORKING=yes

HOSTNAME=centos61.com

（三）centos7系统主机名称永久修改

要修改两处

[root@centos71 ~]# cat     /etc/hostname

centos71.com

[root@centos71 ~]# sed -i  s@@@g   /etc/hostname

[root@centos71 ~]# cat     /etc/hostname

centos7.com

[root@centos71 ~]# hostnamectl    set-hostname  centos7.com
 
[c:\~]$ 

Connecting to 10.0.0.200:...

Connection established.

To escape to local shell, press Ctrl+Alt+].

WARNING! The remote SSH server rejected X11 forwarding request.

Last login: Thu Dec   ::  from 10.0.0.1

[root@centos7 ~]# host

-bash: host: command not found

[root@centos7 ~]# hostname

centos7.com
 
 
 
 

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