• What are permissions? In the management of multi-user computer systems, permissions mean that a particular user has the right to use certain system resources, such as folders, the use of certain system instructions, or storage limits.
• Linux has read, write, and execute permissions respectively:
• Permissions: For folders, read permissions affect whether users can list directory structures. For files, read permissions affect whether users can view file contents
• Write permission: For folders, the write permission affects whether users can create/delete/copy to/move documents in folders. For files, the write permission affects whether users can edit files
• Execution permissions: generally for files, especially script files.

• To set permissions, you need to know some basic file properties and permissions assignment rules. In Linux,lsThe command is used to display the file name and related properties.

Ls-l = ls-lCopy the code

• The part highlighted in red is the document permission attribute information for Linux.

• In LinuxUser, user group, and other concepts, each of them has different permissions. For a document, its permissions are assigned as follows:
  
  
  
  Ten characters indicate meaning:
• The first1Bit: indicates the document type. The common value is”D for folder“,”- Indicates a file“,”L indicates soft connection“,”S stands for socket“And so on;
• The first2-4Bit: indicates the permissions of the document owner, the first2Bit indicates the read permission. The value isR, -; The first3Bit indicates write permission,wMeans writable,-It means not writable, number one4Bit indicates the execution permission. The value can beX, -.
• The first5 to 7Bit: indicates the permissions of users in the same group as the owner, the first5Bit indicates the read permission. The value isR, -; The first6Bit indicates write permission,wMeans writable,-It means not writable, number one7Bit indicates the execution permission. The value can beX, -.
• The first8-10Bit: indicates the prefix except above2Part of the user other than the permission of other users, no8Bit indicates the read permission. The value isR, -; The first9Bit indicates write permission,wMeans writable,-It means not writable, number one10Bit indicates the execution permission. The value can beX, -.

• Permission assignment, both yesrwxIs a combination of three parameters, and the position order does not change. If no corresponding permission is available, use – instead.
• For example: What are the following document permissions?
  
  
• A. It is the folder type
• B. Owner: Has all permissions (read/write execution)
• C. Group user: Readable and executable
• D. Other users: Readable and executable

• For whom to set:
  
  u: Indicates the ownerowner(user)
  
  g: sets the user group to the owner (group)
  
  oSaid:othersTo set permissions for other users
  
  aSaid:all, to all (includingugoSet permissions
• If the permission is not specified for any user, the permission is set for all users by default
• Permission character:
  
  rRead:
  
  wWrite:
  
  x: Execution
  
  -: indicates no permission
• Permission assignment mode:
  
  +: Indicates that a user is assigned new rights (relative to the current user).
  
  -: Indicates the permission to delete a user (relative to the current user).
  
  =: sets permissions to specific values (result-oriented)
• Need to giveanaconda-ks.cfgFile (-rw-------.). Set permissions to ensure that the owner has all permissions, users in the same group have read and execute permissions, and other users have read-only permissions.
• The answer:
  
  ① # chmod u+x,g+rx,o+r anaconda-ks.cfg
  
  
• 2.# chmod u=rwx,g=rx,o=r anaconda-ks.cfg
  
  
• Tip: When a document has execution permission (any part), its color is green on the terminal.

# chmod ug= RWXCopy the code

• For example: Ifanaconda-ks.cfgThe file has no permissions. Can you use itrootIf the user sets the execution permission for all users, it can be written as
  
  ①# chmod +x anaconda-ks.cfg
  
  ②# chmod a=x anaconda-ks.cfg
  
  ③# chmod a+x anaconda-ks.cfg

• userootThe user creates a folder (/oo), permissions Default, permissions are as follows:
  
  
• Need to be inooCreate files under directory (oo/xx.txt), need to give777Jurisdiction:
  
  
• Switch to thetestThe user (not the document owner, not the same group of users, belongs tootherPart) :
• Problem 1: Whether the test user can open the fileoo/xx.txtFile? [Can open]
• Question 2: Can the test user edit the fileoo/xx.txtFile? 【 can 】
• Problem 3: Can the test user be deletedoo/xx.txtFile? No, creating files/folders, moving files, and renaming files are also not allowed.
  
  
• If you want to delete a file in Linux, you need to check whether the file has the write permission, not whether the file has the corresponding permission.

• Effect: Changes the owner of a document
• Grammar:# chown -r username Specifies the file path
• Case: will just nowrootuser-createdooDirectory, owner changed totest

# chown  test  oo/
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• Question:reboot,shutdown,init,halt,userManagement, in the ordinary user identity is not able to operate, but some special circumstances and need to have execution permission. It is impossible for root to tell its password to ordinary users. How to solve this problem?
• The problem is solvable and can be usedSudo (switch user do)Command to set permissions.sudoYou can have the administrator (rootDefine in advance who can execute certain special commands.
• The defaultsudoPhi is not divided by phirootRules for other users, if you want to use them, configure them firstsudo.
• sudoConfiguration file:/etc/sudoers
  
  
• A. configuresudoPlease use the# visudo"And how to use it after openingvimconsistent
• B. Configure the rights of common users
  
  
• rootIndicates the user name. In the case of a user group, it can be written as% group name“
• ALL: indicates the allowed host (address whitelist).
• (ALL): indicates who executes the command. ALL indicatesrootidentity
• ALL: indicates the commands that can be executed by the current user..“Segmentation
• Case: ItselftestUser cannot add a usersudoConfiguration so that users can be added and passwords can be changed (but notrootUser password).
• Note: in writingsudoWhen writing rules, it is not recommended to write direct commands, but to write the full path of the command.
• Paths can be usedwhichCommand to view
• Grammar:# which directive name
  
  
  
  
  
  
• After adding the corresponding rules, you can switch users to ordinary userstest, and then execute:
  
  
• To use the previous rule, run the following command:

# sudo command to executeCopy the code

• After entering the sudo command, enter the current user password for confirmation (not root password), which is not required for the sudo command to be executed again within 5 minutes.
• Pay special attention to: In accordance with the requirements of the case, it is not allowedtestThe user to changerootPassword, so the rule needs to be adjusted, otherwise it can change the root password:
• From modificationrootConfiguration of passwords (first allow all, then denyrootPassword setting) :
  
  /usr/bin/passwd [A-Za-z]*, ! /usr/bin/passwd root
• Addendum: How do I check what special permissions I have under ordinary users?

# sudo  -l
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• Pay attention to:sudoNot common to any Linux branch, commoncentoswithubuntuThere aresudoCommand.