Usage of CHMOD and chown commands

I. CHOWN command

Purpose:Change the file owner or group.The command is composed of the word change owner.

Example:

1. Change the file owner:

Chown Jim program. c

The owner of the file program. C is changed to Jim. As the owner, Jim can use the CHMOD command to allow or deny other users access to program. C.

2. Change the directory owner:

Chown-r JOHN: build/tmp/src

Change the owner and group of all files in the/tmp/src directory to user John and group build

-R recursively changes the owner of all subdirectories and files under a specified directory.

-V: displays the work done by the CHOWN command.

Ii. chmod command

Purpose: Change the access permission of a file or directory.

This command has two usage methods:
One is the text setting method that contains letters and operator expressions, and the other is the number setting method that contains numbers.

1. text setting

Chmod [who] [+ |-| =] [mode] File Name

The meaning of each option in the command is:

The operator who is one of the following letters or their combination:

U indicates "user", that is, the owner of a file or directory.

G indicates "group users", that is, all users with the same group ID as the file owner.

O indicates "Other (Others) Users ".

A Indicates "All (all) Users ". It is the default value of the system.

The operation symbol can be:

+ Add a permission.

-Cancel a permission.

= Grant the given permission and cancel all other permissions (if any ).

Set the permissions indicated by mode to any combination of the following letters:

R readable.

W writable.

X executable.

X adds the X attribute only when the target file is executable to some users or the target file is a directory.

S sets the owner or group ID of the process to the file owner during file execution. In the format of "U + S" to set the user ID of the file, and "G + S" to set the group ID.

T save the program text to the swap device.

U has the same permissions as the file owner.

G. users in the same group have the same permissions as file owners.

O has the same permissions as other users.

File Name: list of files separated by spaces to change permissions. Wildcards are supported.

Multiple permission methods can be provided in a command line, separated by commas. Example: chmod g + R, O + r example

Grant the same group and other users the permission to read the file example.

2. digit setting

First, we must understand the meaning of the property represented by numbers: 0 indicates no permission, 1 indicates executable permission, 2 indicates writable permission, 4 indicates readable permission, and then add it.

Therefore, the format of the numeric attribute should be three Octal numbers from 0 to 7. The order is (u) (g) (o ).

For example, if you want the owner of a file to have the "read/write" permission, you need to set 4 (readable) + 2 (writable) to 6 (read/write ).

The number setting method is generally in the following format:

Chmod [mode] File Name