Rhel7 operation level introduction and switching operation

init yes ​ ​Linux System ​​​ One of the indispensable procedures in operation .init process , It's a user level process started by the kernel . The kernel will have been used in the past init Look for it in a couple of places , It's in the right place （ Yes ​ ​Linux​​ system ） yes /sbin/init. If the kernel cannot be found init, It will try to run /bin/sh, If the run fails , The startup of the system will also fail .

Linux System 7 Operating levels

0： To turn it off , Shutdown mode

1： Single user mode

2： Multi user mode

3： Complete multi-user text mode

4： The system is not in use , It's not necessary to keep it

5： Graphic mode

6： Restart mode

The runtime level is the functional level that the operating system is currently running . This level goes from 0 To 6, It has different functions .

Level specific description ：

0： System shutdown （ To turn it off ） Pattern , The system default run level cannot be set to 0, Otherwise it will not start properly , Turn it off automatically as soon as you turn it on .

1： Single user mode ,root jurisdiction , For system maintenance , No remote login , It's like Windows Under security mode login .

2： Multi user mode , No, NFS Network support .

3： Complete multi-user text mode , Yes NFS, Enter the console after logging in ​ ​ command ​​ Row mode .

4： The system is not in use , It's not necessary to keep it , In some special cases, you can use it to do something . For example, when the battery of a laptop is exhausted , You can switch to this mode to make some settings .

5： Graphic mode , Log in and enter the figure GUI Mode or GNOME、KDE Graphical interface , Such as X Window System .

6： Restart mode , The default run level cannot be set to 6, Otherwise it will not start properly , It will always be on and on .

Introduction to starting principle ：1、 In the catalog /etc/rc.d/init.d There are many servers under ​ ​ Script ​​ Program , It's generally called service (service).

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        [[email protected] ~]# ls -l /etc/rc.d/init.d
        
total 40
        
-rw-r--r--. 1 root root 15131 Sep 12  2016 functions
        
-rwxr-xr-x. 1 root root  2989 Sep 12  2016 netconsole
        
-rwxr-xr-x. 1 root root  6643 Sep 12  2016 network
        
-rwxr-xr-x. 1 root root  2190 May 31 02:09 nginx
        
-rw-r--r--. 1 root root  1160 Sep 13  2016 README
        
-rwxr-xr-x. 1 root root  2437 Jun 26  2015 rhnsd
       
       

        
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2、 stay /etc/rc.d There are 7 One is called rcN.d The catalog of , Corresponding to the 7 The first level of operation is (0-6).

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        [[email protected] ~]# ls -l /etc/rc.d
        
total 36
        
drwxr-xr-x. 2 root root 4096 May 31 02:09 init.d
        
drwxr-xr-x. 2 root root 4096 May 30 11:46 rc0.d
        
drwxr-xr-x. 2 root root 4096 May 30 11:46 rc1.d
        
drwxr-xr-x. 2 root root 4096 May 31 05:00 rc2.d
        
drwxr-xr-x. 2 root root 4096 May 31 05:00 rc3.d
        
drwxr-xr-x. 2 root root 4096 May 31 05:00 rc4.d
        
drwxr-xr-x. 2 root root 4096 May 31 05:00 rc5.d
        
drwxr-xr-x. 2 root root 4096 May 30 11:46 rc6.d
        
-rw-r--r--. 1 root root  473 Sep 13  2016 rc.local
       
       

        
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Be careful ：
Minimize the installed operating system. By default, there is no graphical software
The method of installing graphical software is as follows

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        yum install -y xorg* gnome* glx*
       
       

        
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RHEL7 Change the default boot level

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        [[email protected] ~]# systemctl get-default 
        
graphical.target
        

        
 Set the default startup to multi-user character interface ：
        
[[email protected] ~]# systemctl set-default multi-user.target 
        
rm '/etc/systemd/system/default.target'
        
ln -s '/usr/lib/systemd/system/multi-user.target' '/etc/systemd/system/default.target'
        

        

        
 Check the operation mode of default startup ：
        
[[email protected] ~]# systemctl get-default 
        
multi-user.target   Character mode 
        

        
 Set the default startup to multi-user graphical interface ： 
        
[[email protected] ~]# systemctl set-default graphical.target 
        
rm '/etc/systemd/system/default.target'
        
ln -s '/usr/lib/systemd/system/graphical.target' '/etc/systemd/system/default.target'
        

        
 Check the operation mode of default startup ：
        
[[email protected] ~]# systemctl get-default 
        
graphical.target   Graphic mode 
        

        

        
 Switch from character interface to graphic interface ：
        
 Method 1： perform  startx
        
 Method 2： perform  systemctl  isolate graphical.target
        
 Method 3： perform  init 5
       
       

        
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summary

That's all RHEL7 Operation level and switching operation , These basic operations are very practical .