File permissions in linux

 In Linux, there are three different types of permissions that can be assigned to files and directories: read, write, and execute. These permissions can be assigned to three different classes of users: the owner of the file or directory, the group that the file or directory belongs to, and all other users.

The following are the different types of file permissions in Linux:

1. Read (r): The read permission allows a user to view the contents of a file or directory. For directories, the read permission allows a user to list the files and directories inside it.

2. Write (w): The write permission allows a user to modify the contents of a file or directory. For directories, the write permission allows a user to create, delete, and rename files and directories inside it.

3. Execute (x): The execute permission allows a user to execute a file or access the contents of a directory. For directories, the execute permission allows a user to access files and directories inside it.

These permissions are assigned to three different classes of users:

1. Owner: The owner of a file or directory is the user who created it. The owner can have any combination of read, write, and execute permissions.

2. Group: A group is a collection of users who share the same permissions to a file or directory. The group can have any combination of read, write, and execute permissions.

3. Others: The others class includes all other users who are not the owner or members of the group. The others class can have any combination of read, write, and execute permissions.

In Linux, file and directory permissions can be set using the chmod command. The chmod command allows you to set permissions for the owner, group, and others, and to set permissions in symbolic or numeric mode.

How to change file permission in linux

The chmod command in Linux is used to change the file permissions of a file or directory. Here are some examples of how to use the chmod command to change file permissions:

1. Changing permissions using symbolic mode:

To change the permissions of a file using symbolic mode, you can use the following command:

chmod [permissions] [file]

For example, to give the owner of a file read and write permissions, and to give the group and others only read permissions, you can use the following command:

chmod u=rw,g=r,o=r [file]

Here, 'u' stands for user, 'g' stands for group, and 'o' stands for others. 'r' stands for read permission, and 'w' stands for write permission. The equals sign '=' sets the permissions, while the comma ',' separates the permissions for different classes of users.

2. Changing permissions using numeric mode:

To change the permissions of a file using numeric mode, you can use the following command:

chmod [numeric permissions] [file]

The numeric permissions are represented by a three-digit number, where the first digit represents the owner's permissions, the second digit represents the group's permissions, and the third digit represents the permissions for others.

Each digit is calculated by adding the values of the permissions you want to assign. 'r' has a value of 4, 'w' has a value of 2, and 'x' has a value of 1. For example, to give the owner read and write permissions, and to give the group and others read permissions only, you can use the following command:

chmod 644 [file]

Here, the first digit represents the owner's permissions (6 = 4 + 2), the second digit represents the group's permissions (4 = 4), and the third digit represents the permissions for others (4 = 4).

Note that you need to have the appropriate permissions to change the file permissions using chmod command.