Briefly introduce chown command

​ ​Linux​​  Every file and directory on the system is owned by someone , Owners have full control over changing or deleting files they own . In addition to having one owner , The file also has an ownership group .

You can use ls -l ​ ​ command ​​ View ownership of files ：

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        [[email protected] Downloads]$ ls -l
        
total 2454732
        
-rw-r--r--. 1 pablo pablo 1934753792 Jul 25 18:49 Fedora-Workstation-Live-x86_64-30-1.2.iso
       
       

        
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The third and fourth columns of the output are owning users and groups , Together they are called ownership . The one above ISO Documents are both pablo.

Ownership is set by chmod Command to set , Control who is allowed to perform reads 、 Write or run operations . You can use chown Order a change of ownership （ One or both ）.

Ownership often needs to change . Files and directories are always in the system , But users are constantly changing . When files and directories move around the system , Or moving from one system to another , Ownership may also need to be changed .

The ownership of files and directories in my home directory is my users and my main groups , With user:group Formal representation of . hypothesis Susan Managing Delta Group , The group needs to edit a file named mynotes The file of . You can use chown Command to change the user of the file to susan, Group changed to delta：

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        $ chown susan:delta mynotes
        
ls -l
        
-rw-rw-r--. 1 susan delta 0 Aug  1 12:04 mynotes
       
       

        
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When the file is set Delta Group time , It can be assigned back to me ：

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        $ chown alan mynotes
        
$ ls -l mynotes
        
-rw-rw-r--. 1 alan delta 0 Aug  1 12:04 mynotes
       
       

        
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Add a colon after the user （:）, You can assign users and groups back to me ：

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        $ chown alan: mynotes
        
$ ls -l mynotes
        
-rw-rw-r--. 1 alan alan 0 Aug  1 12:04 mynotes
       
       

        
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By prefixing the group with a colon , You can change only groups . Now? ,gamma Members of the group can edit the file ：

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        $ chown :gamma mynotes
        
$ ls -l
        
-rw-rw-r--. 1 alan gamma 0 Aug  1 12:04 mynotes
       
       

        
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chown Some of the additional parameters of can be used on the command line and ​ ​ Script ​​ in . Like many others Linux command ,chown There is a recursive parameter （-R）, It tells the command to enter the directory to operate on all the files in it . No, -R sign , You can only change the permissions of the folder , It doesn't change the files . In this example , Suppose the purpose is to change the permissions of the directory and all its contents . Here I add -v（ detailed ） Parameters , In order to chown Report on their work ：

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        $ ls -l . conf
        
.:
        
drwxrwxr-x 2 alan alan 4096 Aug  5 15:33 conf
        
conf:
        
-rw-rw-r-- 1 alan alan 0 Aug  5 15:33 conf.xml
        
$ chown -vR susan:delta conf
        
changed ownership of 'conf/conf.xml' from alan:alan to  susan:delta
        
changed ownership of 'conf' from alan:alan to  susan:delta
       
       

        
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According to your role , You may need to use sudo To change the ownership of the document .

When changing the ownership of a file to match a specific configuration , Or when you don't know the ownership （ For example, running ​ ​ Script ​​ when ）, You can use references （--reference=RFILE）. for example , You can copy another file （RFILE, It's called reference ） Users and groups , To undo the changes made above . Think about it , spot （.） Represents the current working directory .

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        $ chown -vR --reference=. conf
       
       

        
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Report changes

Most commands have parameters to control their output . The most common is -v（--verbose） To enable details , however chown Also has the -c（--changes） Parameters to indicate chown Report only when changes are made .chown There will be other reports , For example, operation not allowed .

Parameters -f（--silent、--quiet） Used to suppress most error messages . In the next section , I will use -f and -c, So that only the actual changes .

Keep the root directory

Linux The root directory of the file system （/） Should be highly valued . If the command makes a mistake at this level , Then the consequence may make the system completely useless . Especially when running a command that will recursively modify or even delete .chown The command has a parameter that can be used to protect and maintain the root , It is --preserve-root. If you use this parameter with recursion in the root directory , Then nothing will happen , But there will be a message ：

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        $ chown -cfR --preserve-root alan /
        
chown: it is dangerous to operate recursively on '/'
        
chown: use --no-preserve-root to override this failsafe
       
       

        
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If not with --recursive Use a combination of , Then this option is invalid . however , If the order is made by root User run , be / Your own permissions will be changed , But the permissions of other files or directories under it will not change ：

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        $ chown -c --preserve-root alan /
        
chown: changing ownership of '/': Operation not permitted
        
[[email protected] /]# chown -c --preserve-root alan /
        
changed ownership of '/' from root to alan
       
       

        
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Ownership is security

File and directory ownership is part of good information security , therefore , It's important to occasionally check and maintain file ownership to prevent unnecessary access .chown The order is Linux One of the most common and important commands in the security command set .