File permissions for linux operations

1. Basic permissions UGO

=====================================================

File permission setting: can be assigned to a user or group in which way to access a file

权限对象：
属主------->u
属组------->g
其他人------>o
基本权限类型：
读(read)：r   ---->4
写(write)：w  ---->2
执行: x(exec) ----->1

Case:

r w x        rw-        r--       alice   hr    file1.txt
属主权限    属组权限   其他人权限      属主   属组      文件
​
前提条件：jack属于hr组
一  alice对file1.txt文件有什么权限？
二  jack对file1.txt文件有什么权限？
          a. jack是所有者吗？
          b. jack属于hr组吗？
三 tom对file1.txt文件有什么权限？ 
          a. tom是所有者吗？
          b. tom属于hr组吗？
          c. tom为其他人吗？ 

1.1. Set permissions

Change the owner (owner) and group (group) of the file

chown：

[root@linux-server ~]# chown alice.hr file1.txt  //修改属主、属组
[root@linux-server ~]# chown tom  file1.txt  //修改属主
[root@linux-server ~]# chown .it file1.txt   //只改属组
[root@linux-server ~]# chown -R alice.hr dir1 //递归修改---针对目录

1.2. Change permissions

系统默认目录755 文件644

a. Use symbols

[root@linux-server ~]# chmod u+x file1.txt     //属主增加执行
[root@linux-server ~]# chmod a=rwx file1.txt  //所有人等于读写执行
[root@linux-server ~]# chmod a=- file1.txt   //所有人都没有权限
[root@linux-server ~]# chmod ug=rw,o=r file1.txt  //属主属组等于读写，其他人只读
[root@linux-server ~]# ll
-rw-rw-r--. 1 tom   it      0 Nov  1 15:30 file1.txt

b. Use numbers

[root@linux-server ~]# chmod 644 file1.txt 
[root@linux-server ~]# ll file1.txt 
-rw-r--r--. 1 tom it 0 Nov  1 15:30 file1.txt

2. Permission case UGO

======================================================

2.1. Setting permissions case

Set permissions for the access directory /home/hr of the hr department, the requirements are as follows:

1. The root user and employees in the hr group can read, write, and execute
2. No other users have any permissions

[root@linux-server ~]# groupadd hr   //创建一个用户组
[root@linux-server ~]# useradd hr01 -G hr   //创建hr01用户添加到hr组里
[root@linux-server ~]# useradd hr02 -G hr   //创建hr02用户添加到hr组里
[root@linux-server ~]# mkdir /home/hr       //在/home创建一个hr目录
[root@linux-server ~]# chown .hr /home/hr   //将/home/hr目录的所属组设置为hr
[root@linux-server ~]# chmod 770 /home/hr   //将/home/hr目录的权限设置为770
[root@linux-server ~]# ll -d /home/hr       //查看/home/hr目录本身的权限
drwxrwx---. 2 root hr 6 Nov  1 17:11 /home/hr

The meaning of r, w, x permissions to files and directories

For files:

r----cat

w --- vi 、 vim

x ---- bash /dir/file

To the directory:

r --- ls

w -----touch、rm

x ---- cd

2.2.rwx's impact on files

Practical case 1: the impact of rwx on files

[root@linux-server ~]# vim /home/file1
date
[root@linux-server ~]# ll /home/file1 
-rw-r--r--. 1 root root 5 Nov  3 15:19 /home/file1
​
[root@linux-server ~]# su - alice  #切换普通用户
[alice@linux-server ~]$ cat /home/file1 
date
[alice@linux-server ~]$ /home/file1   #执行文件
-bash: /home/file1: Permission denied
[alice@linux-server ~]$ exit
logout
[root@linux-server ~]# chmod o+x /home/file1
[alice@linux-server ~]$ /home/file1 
Sun Nov  3 15:26:21 CST 2019
​
[root@linux-server ~]# chmod o+w /home/file1 
[alice@linux-server ~]$ vim /home/file1
date
123
ls

2.3.rwx's impact on directories

Practical case 2: There is no w for directories and rwx for files

[root@linux-server ~]# mkdir /dir10
[root@linux-server ~]# touch /dir10/file1
[root@linux-server ~]# chmod 777 /dir10/file1 
[root@linux-server ~]# ll -d /dir10/
drwxr-xr-x. 2 root root 19 Nov  3 15:37 /dir10/
[root@linux-server ~]# ll /dir10/file1 
-rwxrwxrwx. 1 root root 0 Nov  3 15:37 /dir10/file1
[root@linux-server ~]# vim /dir10/file1
jack
[root@linux-server ~]# su - alice
Last login: Sun Nov  3 15:28:06 CST 2019 on pts/0
[alice@linux-server ~]$ cat /dir10/file1 
jack
[alice@linux-server ~]$ rm -rf /dir10/file1   #权限不够
rm: cannot remove ‘/dir10/file1’: Permission denied
[alice@linux-server ~]$ touch /dir10/file2   #权限不够
touch: cannot touch ‘/dir10/file2’: Permission denied

Practical case 3: There is w for directories, but no permissions for files

[root@linux-server ~]# chmod 777 /dir10/
[root@linux-server ~]# chmod 000 /dir10/file1 
[root@linux-server ~]# ll -d /dir10/
drwxrwxrwx. 2 root root 19 Nov  3 15:38 /dir10/
[root@linux-server ~]# ll /dir10/file1 
----------. 1 root root 5 Nov  3 15:38 /dir10/file1
[root@linux-server ~]# su - alice   #切换普通用户
Last login: Sun Nov  3 15:38:53 CST 2019 on pts/0
[alice@linux-server ~]$ cat /dir10/file1 
cat: /dir10/file1: Permission denied    #没有权限
[alice@linux-server ~]$ rm -rf /dir10/file1 
[alice@linux-server ~]$ touch /dir10/file2
小结
对目录有w权限，可以在目录中创建新文件，可以删除目录中的文件（跟文件权限无关）
注意事项
文件： x 权限小心给予
目录： w 权限小心给予

3. Basic access ACL

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File permission management: ACL sets basic permissions (r, w, x).

UGO sets basic permissions: Only for one user, one group and other people.

Setting method:

[root@linux-server ~]# touch /home/test.txt
[root@linux-server ~]# ll /home/test.txt 
-rw-r--r--. 1 root root 0 Nov  3 15:53 /home/test.txt
[root@linux-server ~]# getfacl /home/test.txt  #查看文件的facl权限
getfacl: Removing leading '/' from absolute path names
# file: home/test.txt
# owner: root
# group: root
user::rw-
group::r--
other::r-- 
​
[root@linux-server ~]# useradd jack
[root@linux-server ~]# setfacl -m u:alice:rw /home/test.txt   //增加用户alice权限
[root@linux-server ~]# setfacl -m u:jack:- /home/test.txt     //增加用户jack权限
[root@linux-server ~]# setfacl -m g:hr:r /home/test.txt       //增加组的权限
[root@linux-server ~]# setfacl -m o::rw /home/test.txt
​
-m, --modify  modify the current ACL(s) of file(s)

3.2. View/Delete:

[root@linux-server ~]# ll /home/test.txt 
-rw-r-rw-+ 1 root root 4 Nov  3 15:58 /home/test.txt
[root@linux-server ~]# getfacl /home/test.txt 
getfacl: Removing leading '/' from absolute path names
# file: home/test.txt
# owner: root
# group: root
user::rw-
user:alice:rw-
user:jack:---
group::r--
group:hr:r--
mask::rw-
other::rw-
[root@linux-server ~]# setfacl -x u:alice /home/test.txt
[root@linux-server ~]# setfacl -x g:hr /home/test.txt
 -x：--remove
[root@linux-server ~]# getfacl /home/test.txt 
getfacl: Removing leading '/' from absolute path names
# file: home/test.txt
# owner: root
# group: root
user::rw-
user:jack:---
group::r--
mask::r--
other::rw-
[root@linux-server ~]# setfacl -b /home/test.txt  #取消所有的facl权限
-b, --remove-all

ACL extension mask

用于临时降低用户或者组（除属主和其他人）的权限
#建议方便管理其他人权限设置为空
实验：
[root@localhost ~]# touch /home/file1
[root@localhost ~]# setfacl -m u:alice:r /home/file1
[root@localhost ~]# setfacl -m u:tom:rw /home/file1
[root@localhost ~]# setfacl -m g:hr:rwx /home/file1
[root@localhost ~]# getfacl /home/file1
getfacl: Removing leading '/' from absolute path names
# file: home/file1
# owner: root
# group: root
user::rw-
user:alice:r--
user:tom:rw-
group::r--
group:hr:rwx
mask::rwx
other::r--

Open a terminal

[root@localhost ~]# su - alice
[alice@localhost ~]$ cat /home/file1
回到原来终端
[root@localhost ~]# setfacl -m m::r /home/file1   #m表示mask
[root@localhost ~]# getfacl /home/file1
getfacl: Removing leading '/' from absolute path names
# file: home/file1
# owner: root
# group: root
user::rw-
user:alice:r--
user:tom:rw-            #effective:r--
group::r--
group:hr:rwx            #effective:r--
mask::r--
other::r--
测试
[root@localhost ~]# su - tom  
[tom@localhost ~]$ vim /home/file1