Chmod permission change command

Chmod command for permission change-general Linux technology-Linux technology and application information. The following is a detailed description. After having been in touch with linux for so long, I only know that chmod is used to change permissions. The most commonly used is chmod + x file, or chmod 777 file. Now let's take a look at the essence.

In general, three users can operate the file:

U file owner
G same group users
O other users
A All users (file owner, users in the same group, and other users)

Operations that can be performed include '+' (adding permissions), '-' (canceling permissions), and '=' (setting permissions ).

Permission refers to the r read permission, w write permission, and x execution permission. In absolute mode, each permission bit is represented by an octal number. For example, 0400 indicates that the file owner is readable, 0200 indicates that the file owner is writable, and 0100 indicates that the file owner is executable.

In addition, 0040 indicates that users in the same group are readable, 0020 indicates that users in the same group are writable, and 0010 indicates that users in the same group are executable.

0004 indicates that other users are readable, 0002 indicates that other users are writable, and 0001 indicates that other users are executable.

Now, you can easily understand the read, write, and execute permissions as follows: 4, 2, and 1, for example, chmod 755 file.

7 = 4 + 2 + 1 indicates that the file owner has the read, write, and execute permissions.

5 = 4 + 1 means that users in the same group and other users have read and execute permissions.

Then you can use the chmod command flexibly based on the specific problem.