First part shell
Chapter 1 file security and authority
1.1 file
When you create a file, the system saves information about the file, including:
File location
file type
File length
Which users have this file, which users can access the file
i node
Document modification time
File permission bit
1.2 file type
d catalog
l Symbol link (pointing to another)
S socket file
B block device file
C character device file
p Named pipe file
- ordinary document
1.3 permission
In addition to the front "-", a total of 9 characters, respectively correspond to 9 rights, respectively, can be divided into 3 groups.
R Read Permissions W Write / Change Permissions x Permission to execute this script or program
The first group defines the file genus
The second group defines the file owner's default group permissions
The third group defines the permissions of other users in the system
1.4 change power limit
CHMOD changes the permission bit of the file, there is absolute mode and symbol mode.
1.4.1 symbol mode
The general format of the chmod command is:
Chmod [Who] Operator [Permission] FileName
The meaning of WHO is:
u Document host
G in the same group user permissions
o Other user rights
a all user rights
The meaning of Operator is:
Increase permissions
- Cancel permissions
= Set permissions
The meaning of Permission:
R read rights
W Write Permissions
X execution permission
S file owner and group set-id
T viscous position
L Plus the file to make other users can't access
U, G, O for file owners, the same group users and other users
1.4.2 CHMOD command example
Assuming that the file MyFile file has this permission: RWX RWX RWX:
CHMOD A-X myfile Reclaims All User Execution Permissions
1.4.3 absolute mode
The general form of the chmod command absolute mode is: chmod [mode] file where MODE is an octave.
In absolute mode, each permission bit is indicated by an eight-input number.
0400 file owner can read 0010 The same group can be executed
0200 file owner can write 0004 Other users to read
0100 file owner can execute 0002 other users can write
0040 Group User Readable 0001 Other Users Executive
0020 The same group can write
When setting the permission, simply use the number of permissions corresponding to it, add it, it is the corresponding permission bit.
1.5 directory
The permission bit of the directory is different. The permission bit of the file is different. The read rights of the directory means that the contents can be listed. Write permissions mean that files can be created in this directory, and the execution rights limit means searching and accessing the directory. The permissions of the directory will overwrite the permissions of files in the directory.
