Linux系统重要文件（三）

---

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