Linux Shell Programming Notes-File security and permissions __ block chain

1, Documents: 1.1, the file access to 3 kinds of ways:
1 read (show file contents), 2 write (edit, delete, modify permission), 3 execute (Run shell script, program, etc. executable files).
1.2, the file can be divided into 3 kinds of permissions:1 The file is the main 2) the same group of users 3 other users.
The permissions of a file are represented by a 9-bit permission bit, which can be seen through list-l.
1.3. File type:A flag number in front of the 9-bit permission bit that represents the type of file. 1.4, the file type of Linux:
D Directory
L Symbolic Link (point to another file)
s socket file
B Block Device file
C Character device file
P Named pipe file
-Common documents
1.5, create the file:
Touch filename
1.6, change the file permission bit:
chmod [who]operator[permission] filename #命令格式;
chmod g-w myfile #修改单个文件的权限;
chmod g-w ~/documents/shellt/* #修改目录下所有文件的权限;
Chmod-r g-w ~/documents/shellt/* #修改目录下及子目录下的所有文件的权限;
2, Table of contents:
2.1, the Directory access to 3 kinds of permissions:1), read (the contents of the list), 2, write (can be created in the file); 3 Execute (searchable and accessed the directory);
Access to the directory overrides the access rights of the files in the directory.
3, suid, GUID permission bit:
The X permission on the file's permission bit, which becomes S. The following figure: Ping this shell file has the S permission bit.

The meaning of the suid permission bit: If a shell script is set to be such a permission, other users will also have the permissions of the primary user when executing the file. Suid permission bits are often used to perform database backups or other administrative work in a Linux cluster.
chmod u+s <filename> #用符号方式设置文件具有suid权限位, but before setting up, you must ensure that the file has X permissions.
4, the ownership of the document:
When a user creates a file, the user is the owner of the file and owns the file;
Only the primary user and the system administrator can change the ownership of the file;
chmod [-R] [h] who file #可选:-r contains the files under the subdirectory,-H does not affect the target file of the symbolic connection;
CHGRP [-R] [-h] who file
View information about the user group for the current user:

5, the user creates the file the default permission configuration (umask):
When each user is created, the user is set to create a default configuration for the file. When a user creates a new file, they do not need to specifically specify the access rights of the file.
6. Symbolic Link:
Symbolic links are: soft links (pointers to files), hard connection, the target of symbolic links are 2 kinds: directories, files;
Use the soft link of the file to realize multiple images of the file, modify the source file, and the image file will be modified accordingly;
Ln-s Source_path Target_path #创建软链接;