I. Syntax format: chmod [who] [opt] [mode] File/directory name
1. which indicates the object, which is one or a combination of the following letters:
U: indicates the file owner.
G: indicates the same group of users.
O: other users
A: indicates all users. 2. Opt indicates the operation, which can be:
+: Add a permission.
-: Cancel a permission.
=: Grant the given permissions and cancel the original permissions.
3. mode indicates the permission:
R: readable
W: writable
X: executable
For example, to add the read and write permissions for file a.txt to users in the same group:
Chmod g + RW a.txt
Ii. digit setting
The number setting rule is simpler: chmod [mode] File Name
The key is the mode value. At first many beginners will be confused. In fact, it is very simple. We regard rwx as a binary number. If there is 1, there is 0, then rwx R-x r--can be expressed:
111 101 100
Convert each three digits into a decimal number, that is, 754.
For example, we want to grant the permission for the.txt file:
Other users in the same group
Readable is yes
Writable is executable
Then, we first obtain the permission string RW-r -- Based on the table above, and convert it to the binary number 110 110 100, and then convert each three digits into a decimal number, we get 664, So we run the following command:
Chmod 664 a.txt
The calculation process is as follows:
1) 1 + 2 + 4 = 7
2) The user group with 2 + 4 = 6 permission bits should be set to 6 and can be read and written.
3) 4. Other users are readable.
The commonly used numeric value and its meaning:
-RW ------- (600) -- only the owner has read and write permissions.
-RW-r -- (644) -- only the owner has read and write permissions, while the owner and other users have only read permissions.
-Rwx ------ (700) -- only the owner has read, write, and execution permissions.
-Rwxr-XR-X (755)-the owner has the read, write, and execution permissions, while the owner and other users have only the read and execution permissions.
-Rwx -- X (711) -- the owner has read, write, and execution permissions, while the owner and other users have only execution permissions.
-RW-(666) -- all users have the permission to read and write files. This approach is not advisable.
-Rwxrwxrwx (777)-all users have read, write, and execute permissions. It is not advisable.
The following are two common settings for the directory:
Drwx ------ (700)-only the owner can read and write data in the directory.
Drwxr-XR-X (755)-All users can read this directory, but only the owner can change the contents in the directory.
Chmod permission settings
