Summary of knowledge points about file permissions in Linux learning

Any file in Linux has three permissions of "user, user group and other users". A user can belong to multiple user groups. All user related information is recorded in the /etc/passwd file, passwords are recorded in the /etc/shaodw file, and user groups are recorded in /etc/group document.

The root user has the highest permissions, not counting other users

File attributes

ls -al
-rw-r--r--@  1 zhoust  staff   58503 Dec  8 07:50 antigen.zsh
drwxr-xr-x   2 zhoust  staff      64 Apr 10 18:19 database
drwxr-xr-x   6 zhoust  staff     192 Apr  9 22:12 h5
drwxr-xr-x   4 zhoust  staff     128 Nov 20 16:15 logs
drwxr-xr-x   3 zhoust  staff      96 Mar 18 17:42 node_modules
-rw-r--r--   1 zhoust  staff     320 Mar 18 17:08 package-lock.json
drwxr-xr-x   7 zhoust  staff     224 Dec  8 07:20 software
drwxr-xr-x   9 zhoust  staff     288 Nov 20 16:32 store
drwxr-xr-x   3 zhoust  staff      96 Apr  4 15:43 vkds
drwxr-xr-x   8 zhoust  staff     256 Oct 23 15:06 照片
drwxr-xr-x  12 zhoust  staff     384 Apr 19 08:36 学习视频

It is divided into seven parts:

1. File types and permissions
   File types: ordinary files (-), directory files (d), link files (l)
   Permissions: current user, same user group permissions and other user permissions, rwx is expressed in numbers as 421
2. How many file names are linked to this node (inode)
3. The user name that owns the file
4. The file User group to which it belongs
5. File size: Default is Byte
6. Creation time

7. File name

   Related tutorials:Linux video tutorial

rwx The meaning of files and directories

For files, w means that the content of the file can be modified (But does not include deleting files), x means that the file has the permission to be executed (whether it can be executed actually depends on the content of the file).

The directory is mainly responsible for recording the file name list

• r: means that the directory structure can be read
• w: Files (or directories) in this directory can be deleted, added, modified, moved, renamed, etc., with extremely high permissions
• x: Can enter This directory

If the user only has r permission on a certain directory, he can only view the file name and type in the directory, not even the file size and various attributes. For example, the zst user only has read permissions for the /home/zhoust directory and can only see the file names in this directory.

[zhoust@MyPersonalCentOS ~]$ ls -al
total 36
drwxr-xr--  5 zhoust zhoust 4096 Apr 21 14:55 .

[zst@MyPersonalCentOS ~]$ ls -l /home/zhoust/
ls: cannot access /home/zhoust/learn: Permission denied
total 0
d????????? ? ? ? ?            ? learn

The minimum permissions to complete the task

If the user does not have x permissions on a directory, he cannot execute any commands in the directory, nor can he query the contents of files in the directory.

##Read the contents of file1xr-Modify the content of file1xrw-can be entered and modifiedDelete file1 filewx--Be able to enter /dir1 and have directory modification permissions That’s it! Copy file1 to /dir2x#rwxMust be able to read file1 and be able to Modify the data in /dir2##Modify file attributes and permissions

Operation action	/dir1	/dir1/file1	/dir2	Explanation
				You must be able to enter /dir1 to read the file data inside!

Three commands,

chown

, chgrp, chmod respectively represent the user to whom the modified file belongs, the user group to which the modified file belongs, and the modified file permissions

chmod

There are two types of syntax, one is to modify with numbers , the other is to use symbols to modify file permissions. Use numbers to modify, respectively

421

Add the numbers at the corresponding positions, for example:

# 在 /home/zhoust 目录下，其他用户都不可进入
[zhoust@MyPersonalCentOS ~]$ ls -al
drwxrwxr-x  2 zhoust zhoust 4096 Apr 21 14:55 learn

[zst@MyPersonalCentOS ~]$ cd /home/zhoust/
bash: cd: /home/zhoust/: Permission denied

# 使用 chmod 修改为其他用户可进入，zst 就能进入这个目录了
[zhoust@MyPersonalCentOS ~]$ chmod 705 .
[zhoust@MyPersonalCentOS ~]$ ls -al
drwx---r-x  5 zhoust zhoust 4096 Apr 21 14:55 .

Use symbol type to modify file permissions, the format is

[ Scope][Modify][A certain permission]

, u belongs to the user, g user group, o other users, a all users , the symbols used for modification are -=, and the permissions are still the three rwx. Now turn off other user permissions of the /home/zhoust directory:

[zhoust@MyPersonalCentOS ~]$ chmod o-rx .
[zhoust@MyPersonalCentOS ~]$ ls -al
total 36
drwx------  5 zhoust zhoust 4096 Apr 21 14:55 .

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