0715RHCSA

Soft link and hard link

 

Explanation of the first level catalogue  

/bin：
bin yes Binaries ( Binary ) Abbreviation , This directory holds the most frequently used commands .

/boot：
What's stored here is startup Linux Some of the core files used , Including some connection files and image files .

/dev ：
dev yes Device( equipment ) Abbreviation , What is stored in this directory is Linux External equipment of , stay Linux The way to access devices and files in is the same .

/etc：
etc yes Etcetera( wait ) Abbreviation , This directory is used to store all configuration files and subdirectories required by system management .

/home：
User's home directory , stay Linux in , Each user has its own directory , Generally, the directory name is named after the user's account , As shown in the figure above alice、bob and eve.

/lib：
lib yes Library( library ) This directory contains the most basic dynamic connection shared library of the system , Its function is similar to Windows Inside DLL file . These shared libraries are required for almost all applications .

/lost+found：
This directory is usually empty , When the system is shut down illegally , Here are some files .

/media：
linux The system will automatically identify some devices , for example U disc 、 Optical drive and so on , When identified ,Linux Will mount the identified device to this directory .

/mnt：
The system provides this directory for users to temporarily mount other file systems , We can mount the CD-ROM drive on /mnt/ On , Then enter the directory and you can view the contents of the CD-ROM drive .

/opt：
opt yes optional( Optional ) Abbreviation , This is the directory where the additional software is installed for the host . For example, you install a ORACLE The database can be placed in this directory . The default is empty .

/proc：
proc yes Processes( process ) Abbreviation ,/proc It's a pseudo file system （ Virtual file system ）, It stores a series of special files about the running state of the current kernel , This directory is a virtual directory , It's a mapping of system memory , We can get system information by directly accessing this directory .
The contents of this directory are not on the hard disk but in memory , We can also modify some files directly

/root：
This directory is for system administrator , Also known as the user's home directory for super users .

/sbin：
s Namely Super User It means , yes Superuser Binaries ( Super user binaries ) Abbreviation , Here is the system management program used by the system administrator .

/selinux：
This directory is Redhat/CentOS Unique directory ,Selinux It's a security mechanism , Be similar to windows The firewall of , But this mechanism is more complicated , This directory is for storing selinux Related documents .

/srv：
This directory stores some data that needs to be extracted after the service is started .

/sys：

This is a Linux2.6 A big change in the kernel . This directory has 2.6 A new file system in the kernel sysfs .

sysfs The file system integrates the following 3 File system information ： For process information proc file system 、 For equipment devfs File system and for pseudo terminal devpts file system .

The file system is an intuitive reflection of the kernel device tree .

When a kernel object is created , The corresponding files and directories are also created in the kernel object subsystem .

/tmp：
tmp yes temporary( temporary ) This directory is used to store some temporary files .

/usr：
usr yes unix shared resources( Shared resources ) Abbreviation , This is a very important Directory , Many of the user's applications and files are in this directory , Be similar to windows Under the program files Catalog .

/usr/bin：
Applications used by system users .

/usr/sbin：
Super users use more advanced hypervisors and system daemons .

/usr/src：
The default placement directory for kernel source code .

/var：
var yes variable( Variable ) Abbreviation , There is something expanding in this catalog , We are used to putting the frequently modified directories in this directory . Including various log files .

/run：
It's a temporary file system , Information since the storage system started . When the system restarts , The files in this directory should be deleted or erased . If you have /var/run Catalog , It should point to run.

Redirect ：

• ​ >

The standard output information after the command is executed is not displayed on the default screen , Instead, write to the In the specified file , If the specified file does not exist , Then automatically create the file

 2>

Redirect the error output of the command execution to the specified file , If the file already contains data , The original data will be cleared , Write new data again .

 &> 

• &

• take 1 Redirect to file , take 2 Redirect to 1 

        2>>

• Redirect the error output of the command execution to the specified file , If the file already contains data , The new data will be written to the back of the original content . take 2 Redirect to file , take 1 Redirect to 2 Redirect files to 0 cat Read content from standard input , Then output to a file

create a file , Delete file , Create directory , Delete directory

• touch In two ways ：

1. If the file already exists , Three times to update the file , stat  You can view the details of the file

2. If the file doesn't exist , It means to create a file Create multiple normal files ：

   Method 1： touch file name 1 file name 2 file name 3

   Method 2： touch { file name 1, file name 2, file name 3}

    

   cp Use of commands ：

   grammar ： cp [ Options ] Source file Target file

   Copy file paste rename copy file to directory without changing file properties

   Copy files to directory rename   Copy directory to directory   Copy the file to the directory without changing the file properties

   mv Use of commands

   mv The command is used to cut or rename files , The grammar is ： mv [ Options ] Source file name Target file name The cut operation is different from the copy operation , Because it will delete the source file , Keep only the cut file . If you place a in the same directory A file is cut and pasted into the current directory , In fact, the essence is to rename the file .