Day 6: File Permissions and Access Control Lists

Create a simple file and do ls -ltr to see the details of the files.

Each of the three permissions are assigned to three defined categories of users. The categories are:

 owner   —   The owner of the file or  application.

• "chown" is used to change the ownership permission of a file or directory.

 group   —   The group that owns the file or application.

• "chgrp" is used to change the group permission of a file or directory.

 others  —   All users with access to the system. (outised the users are in a group)

Changing ownership and group:

File Permissions in Linux

There are 3 types of file permissions in Linux:

1. Read (r)

2. Write (w)

3. Execute (x)

You can check the permission allotted to a file using

ls -l [file_name]

To change the file permissions

To change file permissions in Linux, you can use the chmod command. This command allows you to modify the read, write, and execute permissions for the owner, group, and others. The permissions are represented using three characters: r for read, w for write, and x for execute.

chmod u=rwx, g=rwx, o=rwx [file_name]

Here, u stands for user; g for group and o for others.

Changing File Permissions with chmod:

1. chmod +: Adds permissions.

2. chmod -: Removes permissions.

3. chmod =: Sets permissions explicitly.

If you wanna use a number instead of u,g,x then:

Numeric Representation:

• 0: No permissions.

• 1: Execute permission.

• 2: Write permission.

• 3: Write and execute permissions.

• 4: Read permission.

• 5: Read and execute permissions.

• 6: Read and write permissions.

• 7: Read, write, and execute permissions.

chmod 777 [file_name]

Access Control Lists Command (ACL )

Access Control Lists (ACL) allow you to set more specific permissions to a file or a directory without changing the ownership and group. With ACL you can grant or deny permissions to individual users and groups, even when they don't belong to the owner group of the file or directory.

ACL Commands:

1. View ACL for a file or directory:

getfacl filename_or_directory

1. Set ACL for a file or directory:

setfacl -m u:user:rwx,g:group:rx filename_or_directory

1. Remove ACL from a file or directory:

setfacl -b filename_or_directory

1. For adding the permission for user:

setfacl -m u:user:rwx <target_file>

1. For adding permission for the group:

setfacl -m g:group:rwx <target_file>

1. To remove a specify entry:

setfacl -x u:user:rwx <target_file>

1. To remove all entries:

setfacl -b <target_file>

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