Setting permissions in files and folders in Linux

Setting permissions in files and folders in Linux

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Setting permissions in files and folders in Linux

Types of permissions

Linux has three types of permissions that can be assigned to users or groups. These permissions have been described in the table below:

Types of Permissions	Description
Read	The Read permission, represented by "r", allows users or groups to read the files or folders for which this permission has been granted.
Write	The Write permission, represented by "w", allows users or groups to make modifications in the files or folders for which this permission has been granted. This permission also allows deleting files or folders.
Execute	The Execute permission, represented by "x", allows users or groups to execute or search the files or folders for which this permission has been granted.

The permissions on a file or folder are represented in the following format:

rwxrwxrwx

Basically, this is a group of three permissions. The first three characters are for the owner (user) of a file or folder, the next three characters are for a group, and the last three characters are for others.

Setting Permissions on files and folders

Linux uses numbers to set permissions on files and folders. The numbers are from 0 to 7. Each number corresponds to a setting of Read, Write, and Execute permissions.

Following is the number chart of permissions:

Numbers	Read (r)	Write (w)	Execute (x)
0	No	No	No
1	No	No	Yes
2	No	Yes	No
3	No	Yes	Yes
4	Yes	No	No
5	Yes	No	Yes
6	Yes	Yes	No
7	Yes	Yes	Yes

To set the permissions, you use a set of three numbers. The first number belongs to the owner, the second number belongs to a group, and the third to others.


Example

In order to grant Read, Write, and Execute permissions to the owner, to a group, and to others, you will have to set permissions as 777. The first number 7 will provide r, w, x permissions to the owner. The second and third 7s will provide the same permissions to the group and to others, respectively.

Similarly, if you do not want to provide w, r, and x permissions to others, you will have to set the permissions as 770.

Scenario

Problem: You have created a folder named Crack. You want a user named David to become the owner of this folder and have full permissions on it. You also want a group named JAdmin to have Read and Execute permissions. You want to prevent other users from accessing the Crack folder. What steps will you take?

Solution: First of all, you will have to make David the owner of the folder and permit the JAdmin group to access the folder. This can be done by executing the following command:

CHOWN david.jadmin crack

By listing the folder, you will get the following result:

drwxr-xr-x David JAdmin Crack

You can see that David already has r, w, and x permissions, whereas the JAdmin group and others have only r and x permissions. Now, as you do not want to give others any access to the Crack folder, you will have to execute the following command:

CHMOD 750 crack

This will meet all the necessary requirements of the scenario. Listing the folder will provide you the following result:

drwxr-x--- David JAdmin Crack

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