Comprehensive introduction to file permissions and attributes under Linux

In Linux, there is still a lot involved in file permissions. Today I plan to give a systematic and comprehensive introduction.

File permissions and attributes

First let’s take a look at the concepts of owners, groups and other people.

In Linux, every user will belong to a group and is not allowed to be alone outside the group.

• Owner, when the user creates a new file, the default owner of the file is the group to which the user

• belongs, when the user creates a new file When a file is entered, the group the file belongs to is the group the user belongs to

• Others. Users who do not enter the owner and group they belong to are other people

File attributes

Let’s use ls to view the file attributes.

# ls -l 1.php
-rw-r--r--   1 root root 106 Apr 15 10:30 1.php
||||||||||   | |    |    |   |      |
12345678910  11 12  13   14  15       16

##1 represents the file type, - represents document. d represents a directory. b represents a block device. 2234 is divided into a group to indicate owner permissions. The current owner permissions are rw 5567 is divided into one group to indicate the permissions of the group it belongs to. The current permissions of the group it belongs to are r 88, 9, and 10 are divided into one group to indicate other People’s permissions, currently other people’s permissions are r##11##12 means that the owner of this file is root 13 means that the group to which this file belongs is root represents the file size in bytes represents the last modification time of the file

Parameter

Meaning

indicates the number of links to this file

## 14

15

修改文件属性

下面将介绍3个命令

• chmod 改变文件或目录的权限

• chown 改变文件所有者

• chgrp 改变文件所属组

首先新建目录和文件

# mkdir study_file 
# echo '学习使用chmod、chown及chgrp' >  study_file/1.txt # 创建文件

改变文件所有者

# chown www study_file/1.txt #改变文件所有者
# ll study_file/1.txt 
-rw-r--r-- 1 www root 34 5月   5 12:22 study_file/1.txt

同时改变所属组和所有者

# chown www:www study_file/1.txt #同时改变文件所有者及所属组
# ll study_file/1.txt 
-rw-r--r-- 1 www www 34 5月   5 12:22 study_file/1.txt

递归修改所有者及所属组

# touch study_file/2.txt
# touch study_file/3.txt
# chown -R www:www study_file/  #递归修改
# ll study_file/
总用量 4
-rw-r--r-- 1 www www 34 5月   5 12:22 1.txt
-rw-r--r-- 1 www www  0 5月   5 13:13 2.txt
-rw-r--r-- 1 www www  0 5月   5 13:13 3.txt

使用chgrp改变所属组

# ls -d study_file/ -l
drwxr-xr-x 2 www www 4096 5月   5 13:13 study_file/
 
# chgrp root study_file/
# ls -d study_file/ -l
drwxr-xr-x 2 www root 4096 5月   5 13:13 study_file/

使用chmod改变文件权限，修改权限的方法可以是数字方式，也可以是字母方式。一般我们习惯使用数字方式来设置权限。

# chown -R root:root study_file/
# chmod 700 study_file/ #数字方法设置权限
# ll -d study_file/
drwx------ 2 root root 4096 5月   5 13:13 study_file/
# chmod u=rwx,g=r,o=r 1.txt
# chmod a-x 1.txt
# chmod 600 *.txt
# ll
总用量 4
-rw------- 1 root root 34 5月   5 12:22 1.txt
-rw------- 1 root root  0 5月   5 13:13 2.txt
-rw------- 1 root root  0 5月   5 13:13 3.txt

目录与文件权限的意义

对于目录和文件，rwx是有不同的含义的。下面我做了一个表格，介绍了对于不同类型的权限对于的含义。

文件类型	权限	意义
file	r	cat、less、more等
file	w	vim等
file	x	执行权限
dir	r	ls
dir	w	touch、rm、cp、mv等
dir	x	cd

  

文件默认权限

当我们创建了一个新文件后，一般新文件的权限是rw-r--r--，如果新创建一个目录后，目录的权限为rwx-r-xr-x。这就是文件的默认权限，查看默认权限的方法是使用umask.

# umask -S
u=rwx,g=rx,o=rx

默认权限减去x即为文件的默认权限。

修改默认权限的方法也非常简答，还是使用umask命令

umask 0770

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