chmod Modify File Permissions 777 and 754 for Common Linux Commands

The following command is commonly used:

chmod 777  文件或目录

Example: When chmod 777/etc/squid runs the command, the permissions for the squid folder (directory) are modified to 777 (read, write, executable).

If it is an Ubuntu system, you may need to add sudo to perform:

sudo chmod 777 /etc/squid

At the beginning of a story, there will always be a suspense.

There is a classic passage in the series of cold jokes that only programmers can understand:

Please describe FL in the simplest language.

754.

So what does 754 mean?What does 754 mean?What does 754 mean?

The chmod command is described in detail below.

In the Linux system, the roles and privileges of each user are divided very carefully and strictly. Each file (directory) has access permissions. This mechanism can be used to determine how a user reads, writes, executes a file (directory) in some way.

There are three different types of users who operate on files or directories: file owners, group users, and other users.The highest bit represents the file owner's permission value, the middle bit represents the group user's permission value, and the lowest bit represents the other user's permission value. Therefore, in chmod 777, the three numbers 7 correspond to each of the above three users, each with a permission value of 7.

There are three types of permissions for a file or directory: read-only, write-only, and executable.

According to the table above, the permission combination is the sum of the corresponding permission values, as follows:

7 = 4 + 2 + 1 read and write permissions
5 = 4 + 1 read and run permissions

4 = 4 read-only permissions

So you know   chmod  754  filename  The meaning of the command.

This command means to give the file owner read and write access to the filename file, group users read and run access, and other users read access.

More official, detailed explanations can be found using the following commands:

chmod  --help   perhaps man  chmod